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Pyro Scene

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In this section you will find all the simulation settings that are evaluated together with the emitter settings of the Pyro Emitter or Pyro Fuel tag to calculate the smoke and fire simulation. When the first Pyro Eemitter or Pyro Fuel tag is created in the scene, a Pyro Output object is automatically created, which by default uses these settings from the Simulation/Pyro tab of the Scene Settings.
In short, the Pyro Emitter or Pyro Fuel tag takes care of the creation of smoke, temperature and fuel and the settings linked in the Pyro Scene tab of the Pyro Output object take care of the environmental parameters and the energy within the simulation system. In addition, the Pyro Scene Settings are decisively responsible for the calculation accuracy and the calculation methods of the simulation.

Normally, a Pyro Output object is created automatically, at least when a Pyro Emitter or Pyro Fuel tag is added for the first time. As caches can be created and read via the Pyro Output object and it can also be used in conjunction with Redshift Volume shaders, for example, to render a Pyro simulation, it can also be useful to use several Pyro Output objects in a scene. Each Pyro Output object can be linked to its own Pyro Simulation Settings. The default settings from the Scene Settings are used for this.
However, Simulation Scene Objects can also be linked, which also offer setting options for all simulation parameters. In this way, different simulation settings can be managed in one scene and switched simply by exchanging the link in the Pyro Output object. This also makes it possible to compare different simulation settings, for example, as these can be managed in different Simulation Scene objects. For example, coarser settings for the long shot of an explosion and finer settings for the close-up of the simulation can be managed within a scene.

An existing Pyro Output object can simply be duplicated by copy/paste or Ctrl-Drag&Drop in the Object Manager. Otherwise, you can use the Create Output Object button in the Scene Settings to create a new Pyro Output object (see tab for Simulation/Pyro).

Scene

This is where you link to the settings that are to be used to calculate the Pyro simulation. By default, there is a link here to the Pyro settings that can be found in the Simulation tab of the Scene Settings. This can also be recognized from the outside by the name of the Pyro Output object (Default). The linked settings can be viewed and edited directly by expanding the small triangle in front of the link field.
Alternatively, Simulation Scene objects can also be linked here, which also provide all Pyro Settings. In this way, it is very easy to switch between different setting variants by exchanging the link to different Simulation Scene objects.

Note:The Pyro Output object can only work for a simulation if simulation settings are linked in the Pyro Scene tab. If a Scene link is missing there, e.g. because a previously linked Simulation Scene object has been deleted, a button appears below the link field, which can be used to link the Default Simulation Settings from the Scene Settings again.

Create Output Object

This can be used to create a new Pyro Output object, which can be used to create the caching options for a Pyro simulation and the links to the Pyro Simulation settings. A Pyro Output object is created automatically when a Pyro Emitter tag or Pyro Fuel tag is assigned to an object in the Object Manager for the first time.

Voxel Size[0..+∞m]

The entire simulation is based on a consideration of small spatial sections that are shaped like cubes. We already know this principle from the Volume Builder, which fills a defined volume with voxels. The edge length of these voxel cubes is entered here. The smaller these voxels are, the more detailed and accurate the simulation can be. However, it is also true that larger voxels can make the simulation appear more homogeneous and softer.

Smaller voxels result in increased computing and memory requirements for the simulation, so choose a size that matches the desired effect and is adapted to the scale of your objects.
Also keep in mind that the Voxel Size is also indirectly responsible for the detection of the volume on the object that serves as the emitter for the Pyro simulation. If the Voxel Size is too large in relation to the size and shape of the assigned emitter object (the object that carries a Pyro Emitter or Pyro Fuel tag), not all sections of the object may be used as Pyro emitters. This effect can be optimized by adjusting the Object Fidelity on the Pyro tags. The following figure gives an example of this.


On the left you can see the object used as a Pyro emitter. The image to the right shows the simulation result with a Voxel Size of 5 cm. On the far right you can see the same animation frame, this time with a Voxel Size of 0.5 cm. It can be clearly seen, particularly in the lower area, that the smaller Voxel Size is also better at capturing the object shape, where it appears less smoothed.

The image above shows that not only does the level of detail of the simulation change due to the smaller Voxel Size, but the simulation itself also shows different Temperatures and a different Density distribution. This is because in this case the gaps between the protrusions of the emitter object can no longer be detected as accurately due to the larger Pyro voxels. The amount of emitted Density and the concentration of the emitted Temperature is therefore less accurate and in this example leads to slightly stronger buoyancy and therefore to a higher smoke and fire column when using the larger voxels.

Fluid Force Factor[0.00..+∞]

Here you indirectly specify the mass of the simulated gas and thus the effect that the gas has on other simulation objects, such as Soft Bodies. This value is irrelevant within the Pyro simulation.

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Min Substeps[0..256]

Max Substeps[0..256]

Here you set the number of calculation steps of the simulation during the duration of an animation frame. Since Pyro simulations are always based on the density, as well as the pressures, speeds and temperatures of the last calculation state, more calculation steps per time unit are necessary to calculate a reliable result, especially for explosions and other fast-moving simulations. These settings should therefore be adapted to the speed within the simulation. Otherwise, the simulation may not behave or look realistically. On the other hand, too high values lead to an unnecessary extension of the calculation time.


Here you can see a burning circle spline. The only difference between the images is that 0 Substeps were used on the left and 2 Substeps on the right. Note the visible steps within the rapidly rising flames in the lower left area. On the right, this area appears with a smooth transition. However, it can also be clearly seen that the simulation appears more compact overall due to the higher computational accuracy, as the density resolves more quickly.


Here you can see the same simulation settings of an explosion and the same frame of the simulation in each case. 1 Substep was used on the right, 4 Substeps in the middle and 8 Substeps on the right. Increasing the Substeps leads to more details, especially in the faster moving areas of the simulation, and will show a more realistic result overall.

By specifying two different values for Min Substeps and Max Substeps, you enable the simulation to vary the number of calculation steps depending on the situation. To provide a benchmark for this, the value for Expected Advect Distance (in Voxels) is also used. If the velocities within the simulation are greater than or equal to the distance between the number of voxels specified there, the calculation accuracy of Max Substeps is used in the simulation image. If the simulation slows down over time, correspondingly reduced calculation accuracies between Min Substeps and Max Substeps are then used. Of course, this then has the advantage that the high calculation accuracies are only used in the sections of the simulation that benefit from them. If the simulation slows down, these time phases can be simulated faster and with reduced accuracy without affecting the accuracy of the simulation.

In order to find the optimum ratio between Min Substeps and Max Substeps, you should at least look at the fastest phase of the simulation. In the case of explosions, these are usually the first frames in which, for example, the fireball is converted from temperature and fuel into pressure and then rises upwards. Simulations in which only flames or dense smoke are generated at the emitter, on the other hand, are often relatively uniform in their speed and do not exhibit such a strong speed gradient. However, this can also change quickly due to the use of forces, for example. In such a case, you should also give priority to the time period of the simulation in which the highest velocities are to be expected. Set Min Substeps and Max Substeps to an identical, initially small value in order to force the simulation to use exactly this number of calculation steps per simulation frame, regardless of the order of magnitude of the speeds. If you now discover any artifacts or inaccuracies in the simulation (see also the image examples above), simply increase both values slightly and then run the simulation again. Repeat these steps until you are satisfied with the quality of the simulation. Finally, you can then reduce Min Substeps to a low value, such as 0 or 1. Also remember to adjust the setting for Expected Advect Distance (in Voxels), which is described below.

Expected Advect Distance (in Voxels)[1.00..+∞]

As already explained in the explanations of Min Substeps and Max Substeps, you can use this value to control when the maximum number of calculation steps should be used. Whenever the movements within the simulation bridge a distance from one frame to the next that corresponds to this number of voxels, Max Substeps is used. For smaller distances fromframe to frame, reduced Substeps are used down to Min  Substeps for almost stationary simulations.
Since Expected Advect Distance (in Voxels) depends on the size of the voxels, you should first set the resolution of the simulation via the Voxel Size and then adjust this value accordingly.


Voxel Size 5 cm, Min  Substeps 0 and Max Substeps 8 were used here. Expected Advect Distance (in Voxels) 4 was used on the left, 8 in the middle and 16 on the right. As the value increases, the calculation accuracy decreases for the simulation images in which shorter distances than Voxel Size * Expected Advect Distance are covered. A lower calculation accuracy is often reflected in a larger extension of the simulation (see middle and right illustration).

Force Falloff Samples[1..32]

The simulation can be affected by these Force objects, which you can find under Simulate/Forces:

The area of influence of these forces can be limited at these objects by spatial falloffs. The accuracy of the sampling of these falloff areas is specified by this value per voxel in the simulation tree.
If the number of tree voxels in the volume is increased by reducing the Voxel Size, the number of samples for the reduction areas of the Force objects per volume unit also increases automatically. The setting for the Voxel Count does not play a role here.

Which of the Force objects present in a scene should act on the Pyro simulation can be specified individually via the Forces settings, which are documented a little further down this page.

Field Force Field Samples[1..32]

The Field Force object can, among other things, use objects to create individual forces. For example, a Field Force can be aligned along a spline in order to deflect smoke along the spline curve. Such Field Forces are sampled according to this value per voxel of the simulation tree (see the following section). The principle is the same as for Force Falloff Samples, so the setting for the Voxel  Count is also irrelevant here.

Initial Volume Set

A Volume Set object can be linked here. This can be created by clicking the Set Initial State button and manages the Pyro simulation data of the current animation image. By assigning this data, the Pyro simulation is defined for frame 0 of an animation. The simulation can then use this data directly for the subsequent frames. The simulation properties managed in a Volume Set object, such as the Velocity, Color, Density, Temperature or Fuel, can also be used individually and assigned in the Initial Volume Override settings area. This then also enables the use of Pyro properties that were taken from different simulations or map different phases of a simulation. You will find an example of this a little further down on this page.


On the left is a simulation colored by a Vertex Color tag, in which a sphere serves as the emitter volume. In the middle, a vertical plane has been assigned a Pyro Emitter tag and generates Density and Color information. If a simulation frame of the sphere is now used as the initial state for this simulation, the velocities and colors of both simulations mix at the beginning of the simulation (see right image).

Set Initial State

Clicking on this button creates a Volume Set object, in which the simulation data of the current animation frame is managed as it was generated by the Pyro Emitter tag or Pyro Fuel tag. It does not matter how these properties were configured in the Object Properties of the Pyro Output object. Properties marked Off there are also saved in the Volume Set object if they are used in the Pyro Emitter tag.
A Volume Set object can be assigned as the Inistial Volume Set so that the simulation uses this information directly for the first animation frame and calculates the subsequent simulation based on it.
Further information on the Volume Set object can be found here.

Note:

If your simulation uses an active cache file, no Volume Set object can be created for it. In this case, you must switch off the use of the cache and run the simulation again until the desired frame.

Tree Settings

The simulation uses an adaptive grid of voxels, a so-called Voxel Tree, in the area of the gases. Imagine this area as the air in which the simulation takes pressures, flows, temperatures and density changes into account.
This Voxel Tree continuously changes its size and shape by deleting and adding voxels and thus reacts to the developments within the simulation. There is therefore no predefined volume that surrounds the simulation like an impenetrable cuboid. Depending on the available memory, the smoke and fire simulations can therefore theoretically become arbitrarily large.

Note:Pyro simulations are limited to a maximum memory requirement of approx. 90% of the available VRAM. Information on optimizing the memory requirement can also be found in the explanation of the Draw settings section below.

The size of the voxel cubes from which this voxel tree is composed is specified as the Voxel Size. In order for the voxel tree to be able to react to the shape changes of the simulation, some voxels must always lie outside of a simulated smoke column, for example, in order to be able to send signals to the Voxel Tree when more voxels can be added to the tree or, for example, removed from it again after the dissolution of a simulated cloud.

This buffer of outer voxels on the Voxel Tree is set here via the Padding Mode setting and the Padding value. In addition, each voxel on the tree is divided again into smaller voxels for the simulation calculation. This Voxel Count is also set in this section.


Here you can see the Voxel Tree that defines the area of the simulation. The number and distribution of the voxels in this tree is continuously adapted to the simulation in its interior. In this example, you can clearly see that there appear to be many empty voxels in the outer area. This may be due to an unnecessarily high Padding value or very low Density or Temperature values of the simulation in these areas.
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Padding Mode

The quantity and distribution of the padding voxels in the outer area of the Pyro simulation can be selected automatically or constantly:


Constant mode on the left and Automatic mode for Padding on the right.

Padding[0..8]

This is used to specify the voxel thickness of the outer layer in the Voxel Tree in the Constant Padding Mode setting. For very small Voxel Sizes in combination with very rapidly changing simulations, it may be useful to increase this value in order to be able to react effectively to rapid changes in the shape of the simulation. For slow or very large simulations, however, it may also be useful to reduce the value in order to save memory.

Voxel Count

Here you can choose between two presets to set the number of simulation voxels within each tree voxel. You can choose between 16 and 32 voxels, whereby this number is used along each spatial direction. In the case of the preset 16, this already results in 16*16*16 = 4096 simulation voxels in each voxel cube of the tree.

Please note that a larger number of voxels per tree voxel also means that the areas supplemented in the edge area of a tree voxel become smaller, as this edge area is also based on the size of the voxels. For the simulation of very detailed gases, it can therefore also be useful to set the number of voxels to 32, not only to increase the level of detail within the simulation, but also to optimize the memory requirements of the simulation.

Extra Forces

The following parameters define the environmental forces that are to act on the simulation, including gravity and buoyancy, as well as friction and turbulence forces, but also forces that simulate attractive or repulsive forces within e.g. Temperature or Density.


General

Density Buoyancy[-1000000.00..1000000.00]

The buoyancy force causes objects of lower density in the air (or in liquids) to rise upwards. In our case, this force acts like a gravitational acceleration on the Density particles of the simulation. Negative values cause the Density simulation to rise upwards along the Y-axis direction. Positive values cause the simulated smoke to fall downwards.
Please note that the Temperature of the simulation also affects the Density. The rising heat can therefore cause the smoke to be carried away, even if it should actually fall downwards due to a positive Density Buoyancy. Both effects therefore influence each other.

Temperature Buoyancy[-1000.00..1000.00]

This determines the direction and strength with which the temperatures spread. Normally, warm air rises upwards. This is expressed by a positive value. However, you can also reverse this direction with negative values if, for example, a rocket engine is to be displayed. The actual speed with which the heat rises, for example, also depends on the temperature. A hotter gas rises faster than a cooler gas. The Temperature Buoyancy therefore works like a multiplier and not like an absolute value.


On the left you see a simulation with a Temperature Buoyancy of 0.1, on the right the same simulation with a value of -0.1. The Density Buoyancy is -2 in both cases, but the smoke on the right side also moves downwards with the 'stronger' temperature.

Fuel Buoyancy[-1000000.00..1000000.00]

This determines the direction and intensity of the Fuel Buoyancy. With negative values, the fuel rises along the world Y-direction, with positive values, the fuel sinks downwards. Note that this only applies to the unburned fuel before it is converted to Pressure, Density and Temperature. The effect is therefore particularly visible when a low Fuel Burning Rate is combined with a higher Fuel Set or Fuel Add setting. Since the buoyancy for the density, temperature and fuel can be selected independently of each other, interesting effects can be simulated, such as the heavy ash clouds of a volcanic eruption.


On the left you can see examples of rising (negative values) and falling fuel (positive values). To illustrate this, the Temperature Buoyancy has been set to 0. The possible combinations of different directions and amounts for Density, Temperature and Fuel Buoyancy can be used to illustrate special cases, such as on the right-hand side of the figure.

Here is a simple example scene to simulate heavy ash clouds and a volcanic eruption.



Vorticity Strength[-500.00..500.00]

This parameter controls the general turbulence of the simulation and is applied to each voxel of the simulation. The effect can also be linked to certain properties of the simulation using the following parameters. For example, the turbulence can be made dependent on the temperature or density.


The images show the same simulation, with increasing Vorticity values from left to right. The results are also strongly dependent on the voxel size in the simulation and also on the Substeps, as the particles in the simulation sometimes undergo large changes in their velocity due to the turbulence.
Note:Since this effect affects every voxel of the Pyro simulation, too high values can also lead to unnatural results. In the figure above, this can already be observed in the two simulations in the right half of the image, where the Density and Temperature distributions no longer appear to follow a natural pattern.

Source

Here you can choose which component of the simulation should be used for swirling:

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Source Strength[-100.00..100.00]

Here you set the multiplier for the property of the simulation selected via Source. This value has no meaning for Source None. Please note that the values can vary greatly depending on the Source. While a Density in the range between 1 and 20 is normal, Temperatures are often in the range between 100 and 1000. Accordingly, the Source Strength must also be adjusted individually in order to achieve usable results.

Turbulence

This effect also changes the directions of movement within the simulation, but its structure size can be individually adjusted and animated in comparison to the Vorticity Strength. The effect therefore corresponds functionally more to a noise that shifts the simulation in different directions. For flames, for example, the characteristic flickering can be simulated in this way. However, please also bear in mind that the use of Turbulence can slow down the simulation calculation considerably!


On the left is the simulation without any Turbulence, on the right with a value of 4. For an isolated view of the effect, the Vorticity was set to 0 in both cases.

Smooth Spatially

This option is active by default and smoothes the turbulent structure, which can be used to swirl the simulation. On the one hand, this results in more harmonious structures and transitions in the turbulence. On the other hand, finer turbulence can also be suppressed. The following figure gives an example of this.


On the left is a simulation without smoothing of the turbulence, on the right with active spatial smoothing.

Strength[0.00..+∞]

Here you enter the total strength of the turbulence.

Source

Here you can choose which component of the simulation should control the strength of the turbulence:

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Source Strength[0.00..+∞]

Here you set the multiplier for the property of the simulation selected via Source. This value has no meaning for Source None.

Scale with Velocity

If active, this allows fast areas in the simulation to be swirled more than slow ones.

Velocity Factor[-∞..+∞]

This value regulates how strongly the velocities in the simulation should influence the strength of the turbulence. The fact that negative values can also be used here means that the effect can also be reversed. Areas with slow gas movements are then more turbulently swirled than areas with fast gas movements.

Frequency[0.00..+∞]

As is also known from the Noise shader, the turbulence structure can be varied over time. This frequency value indicates the speed of these changes. Remember that at higher frequencies the changes within the simulation can be accelerated so much that you may have to significantly increase the Substeps so that the simulation can react to these changes in Turbulence.

Octaves[1..2147483647]

This value specifies the depth of detail within the turbulent structure. The lower the value, the more homogeneous and soft-focus the turbulence structure appears. Higher values lead to sharper and more finely branched details. However, this improvement in detail also has limits. Above a certain magnitude, you will no longer notice any change, as the following images show.


To illustrate this, you can see a Noise shader with a turbulence structure on a plane. On the far left, only one Octave was used. The structure appears blurred. 10 Octaves are used in the middle, 20 Octaves on the right. You can see here that the visible depth of detail has not changed significantly between these settings.

Initial Octave Scale[0..+∞%]

This is used to define the overall size of the turbulent structure. The refinements and ramifications of the structure added by the Octaves can be adjusted as required using a separate scaling value.

Incremental Octave Scale[0..+∞%]

Depending on the number of Octaves selected, a kind of tree is created, which is divided more and more finely into branches and twigs and thus represents the turbulent structure. Each calculation step, i.e. when you change from the detailed level of the trunk to the branches, can be scaled differently and also have a different effect on the simulation. The value for Incremental Octave Scale is therefore a multiplier for the size of the previous octave scaling. With an Initial Octave Scale of 0.05, the second octave level would therefore have a size of 0.1 with an Incremental Octave Scale of 2, and so on.

Incremental Octave Strength[0.00..+∞]

The functional principle here corresponds to that of the scaling of the different octaves, except that here it is about the influence or strength of the different octaves on the simulation. With values below 1, the finer structures of the higher octaves would have less effect on the simulation compared to the basic structures of the turbulence. The effect is reversed with values above 1. The fine turbulence structures then have a stronger effect on the simulation in percentage terms. The basis for all strengths is the Strength parameter of this parameter group.

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Shredding

These settings can be used to control additional attraction and repulsion forces within a Pyro component, for example to sharpen flames or smoke.

Push Strength[-∞..+∞]

With this strength, the Pyro component selected for Source repels itself. With the Source Density, clouds can then form, for example, which spread out and lose density in the process. This effect can be limited via the following Push Range setting. In addition, the opposite effect, i.e. an attraction of the selected Source property, can also be simulated via Pull Strength. The ratio between Push and Pull, if both strengths are used simultaneously, can be set via the Source Threshold value.
The following video shows slightly increasing strength values for the repulsion of the Temperature component of a simulation from left to right. This results in faster cooling of some flames and thus also earlier smoke formation (Density).


This example shows increasing values for the Push Strength of a Temperature simulation from left to right.

Push Range[0.00..+∞]

With this value, the repulsion can be applied depending on the Source property values in the simulation. With a value of 0, the repulsion generally acts on the entire property selected at Source in the simulation. With higher values, this formula is used: (Abs(Source Threshold value - property value) / Push Range).
So, for example, if we assume the Temperature as the Source and use a Source Threshold value of 500, the value 500 is calculated in a flame with 1000 degrees (Abs(500-1000) = Abs(-500) = 500). In conjunction with a Push Range of 500, we therefore obtain a multiplier of 1 for the Push Strength. A smaller Push Range therefore increases the intensity of the repulsion, a larger range weakens the repulsion. The following figure shows this effect.


Here, only Density was generated on a sphere. A large Push Strength and a very small Source Threshold were used. The result can be seen on the left with a small and on the right with a large Push Range. The smoke is dispersed to varying degrees.

The following video also compares different Push Ranges, this time with a Temperature simulation. On the far left, the repulsion has an effect through a Push Range of 0 on all temperature ranges of the simulation. On the right, the results of different Push Ranges can be seen. Note that in each case, the Source Threshold value according to the above formula also has a major influence on the effect of this setting.


The exemplary effect of different Push Ranges on a Temperature simulation.

Pull Strength[-∞..+∞]

This strength attracts the Pyro component selected under Source. The Source Temperature can then be used to create more sharply defined flames, for example. This effect can be limited via the following Pull Range setting. In addition, the opposite effect, i.e. a repulsion, can also be simulated via Push Strength. The ratio between the repulsion and the attraction, if both strengths are used simultaneously, can be set via the Source Threshold value.


This example shows increasing values for the Pull strength of a Temperature simulation from left to right.

Pull Range[0.00..+∞]

With this value, the attraction can be applied depending on the Source property values in the simulation. With a value of 0, the attraction generally acts on the entire property selected at Source in the simulation. With higher values, this formula is used: (Abs(Source Threshold value - property value) / Pull Range).
So, for example, if we assume the Temperature as the Source and use a Source Threshold value of 500, the value 500 is calculated in a flame with 1000 degrees (Abs(500-1000) = Abs(-500) = 500). In conjunction with an Pull Range of 500, we thus obtain a multiplier of 1 for the Pull Strength. A smaller Pull Range therefore increases the intensity of the attraction, a larger range weakens the attraction. The following video shows this effect.


This example shows increasing values for the Pull Range of a Temperature simulation from left to right. The value 0, at which all temperature ranges attract, was used on the far left.

Source Threshold[0.00..+∞]

You use this value to create the desired balance between attractive and repulsive forces. If a value measured in the Source property is above the Threshold value, the repulsion is strengthened there. If Source values are lower than the Threshold value, the attractive forces are strengthened there. The following illustration gives an example of this.


Here, equal strength values were used for the repulsion and attraction of the simulated Temperatures. The intensity of the repulsion increases as the Source Threshold value decreases (shown in the figure by the different results from left to right). A larger Source Threshold value (left in the figure) therefore generally strengthens the attractive forces or weakens the repulsive forces.

Maximum Magnitude[0.00..+∞]

Depending on the selected Source property, an upper limit can be set here for the property values read out so that the intensities for attraction and repulsion cannot scale arbitrarily. As explained in the explanation of the Push Range and Pull Range parameters, the currently measured Source property is also included there.

Source

Here you select which property of the simulation the attractive or repulsive effects should affect. In principle, the effect on the Temperature or Density simulation is the most obvious. Since the Fuel is usually burned shortly after it is created, the effects are less noticeable.
Please note that, depending on the selected Source, values for the Push Range and Pull Range, the Source Threshold and the Maximum Magnitude must also be adapted to this property. Temperatures can easily range from 100 to 5000 degrees, whereas the Density is often only in the range between 1 and 20.

Fuel Combustion

The parameters in this section are only relevant if you have fuel generated at the emitter and this is to be burned in the simulation. This can generate additional heat and density, and the pressure within the simulation can also be changed locally. As a result, this area expands, which is useful for displaying explosions or clouds, for example. Fuel can also be interpreted directly as pressure if you have activated Fuel Type Frame Range and Constant Pressure on the Pyro Tag of the emitter object.


Here, a cylinder was defined as the emitter and a certain amount of fuel was abruptly generated on it using the Frame Range method, which is then converted to density and temperature. The increase in pressure during combustion creates the characteristic explosion cloud.

Here you can find an explosion example scene.



Fuel Burning Rate[0.00..+∞]

This describes how much fuel is burned per second. This value can never be higher than the amount of fuel that you have generated via the Pyro Tags. For this reason, the Pyro Emitter Tag or Pyro Fuel Tag also has the Match Burning Rate option, which can be activated with the Continuous Fuel Type, to orient the amount of fuel generated to this parameter so that the same amount of fuel is always generated as can be burned.

Ignition Temperature[-1.00..+∞]

As soon as the temperatures in your simulation are higher than specified here, the fuel is ignited in that area. The absolute value of this temperature is therefore not important. Even at a simulated temperature of only 20°, the fuel can already be burnt if the Ignition Temperature is set to 10°, for example.

Density per Fuel[0.00..+∞]

When a unit of fuel is burned, this density is also created in the simulation. Density is represented as smoke in the simulation.

Temperature per Fuel[0.00..+∞]

When burning one unit of fuel, this temperature is additionally created in the simulation.

Pressure per Fuel[0.00..+∞]

When burning one unit of fuel, this pressure is generated in the simulation. At higher values, the simulation expands abruptly in the area of combustion, which can lead to the typical representation of an explosion. By using the Fuel Type Frame Range and activating Constant Pressure on the Pyro Eemitter Tag or Pyro Fuel Tag, pressure can also be generated directly on the emitter object. In this case, Density and Temperature should already have been emitted in order to be able to blow these elements apart by the pressure.

Rest Grid

This function can be used to calculate additional 3D coordinates for the simulation volume. These can be used by some renderers in a similar way to UVW coordinates, e.g. to use additional deformations or noise structures to refine the simulation. The caching of this Rest Grid structure is activated in the Object section of the Pyro Output object via the option for Dual Rest Grid.


Rest Grid Enabled

This enables the additional calculation of a so-called Rest Grid structure. Similar to UVW coordinates, this vector structure can provide a stationary or moving description of the simulation components. This enables, for example, subsequent deformation or superimposition with noise on a Pyro simulation.
By activating this option, you can also use the caching options for the Dual Rest Grid in the Object settings of the Pyro Output object.

Rest Grid Reset Cycle[4..2147483647]

Here you specify the number of simulation frames after which the Rest Grid structure is updated. This can always be helpful if the shape of the simulation changes quickly. Without updating, the Rest Grid structure would have to be stretched more and more, e.g. on a spreading cloud, which can lead to a distortion of the Rest Grid values. The following figure shows an example of this.


In the example above, a Pyro Emitter tag has been applied to a sphere to create Density. Just above the sphere, the rising smoke is blown to the right by wind along the world x-axis. For this simulation, the Rest Grid option was activated, once with a short Reset Cycle (left in the figure) and then once with a very long Reset Cycle (right in the figure).
To illustrate this, the Rest Grid structure was saved as a cache. Since this is a vector structure, it can also be used as a Color in the Pyro Volume material, for example, to color the smoke in the basic colors accordingly, which was implemented in the figure above. You can clearly see how the original Rest Grid values practically stick to the smoke in the right half of the image and are retained even after the change in direction. During the short Reset Cycle on the left of the image, the Rest Grid values are continuously recalculated and can therefore react in good time to the change in direction and shape of the simulation. The Rest Grid values remain stationary and more independent of the simulation.

Rest Grid Time Scale[0..10000%]

This value is used as a multiplier for the simulation time. Values below 100% slow down the time used for the Rest Grid calculation, values above 100% speed up the simulation time for the Rest Grid.

Density

Here you will find all settings relating to the decrease, smoothing and evaluation of the Density properties of the simulation. The Dissipation settings can be used, for example, to generally limit the spread of the Density and thus the size of the simulated cloud or smoke column, which can have a positive effect on the memory requirements and the simulation speed.

Note:By using the Destructor Force object, a simulation can also be spatially constrained overall.


Relative Density Dissipation[0..100%]

This parameter describes the percentage reduction in Density per frame of the simulation, normalized to a frame rate of 30.


Here, a simple Density emission was simulated on the upper half of a cylinder. All four images show the same point in time of the simulation. The only difference is in the change for Relative Density Dissipation. From left to right, the values 5%, 10%, 15% and 20% were used for this. The value for Absolute Density Dissipation was set to 0 here for clarification. It can be clearly seen how the soft fraying of the cloud is maintained by the percentage reduction in density.

Absolute Density Dissipation[0.00..1000.00]

This setting defines the Absolute Dissipation of the Density per second of the simulation.


Here, a simple Density emission was simulated on the upper half of a cylinder. All images show the same point in time of the simulation. The only difference is the change in Absolute Density Dissipation. From left to right, the values 0, 1, 2, 3 and 4 were used for this. The value for Relative Density Dissipation was set to 0 here for clarification. It is clear that the increase in Absolute Density Dissipation leads to a hard and high-contrast clipping of the simulation.

Density Smooth Factor[0..100%]

As the values increase, the smoothing of the Density values in the simulation increases. The differences between neighboring areas in terms of Density are weakened. As a result, the representation of the Density not only loses sharpness and detail, but the simulation as a whole can also change.


All images show the same simulation, but with increasing values for Density smoothing from left to right. It is also clear that not only does the appearance of the simulation change, but that the changes to the Density distribution also lead to different simulation results.

Density Active Threshold[0.00..+∞]

Only the areas with a Density above this Threshold value are taken into account in the simulation. Used sensibly, this setting can therefore improve the simulation speed and also the memory requirement without losing important details. In addition, deliberately higher values can also lead to stylistically interesting results. You will also find similar threshold values for Temperature and Fuel.


The series of images demonstrates, from left to right, the effect of increasing values for the Density threshold. Areas with low Density are thus gradually filtered out and no longer taken into account by the simulation. This leads to a sharpening of the Density simulation and to an acceleration of the calculation.

Density Cutoff[0.00..+∞]

Information about the Density that lies below this value is deleted within the simulation. For example, if this value is increased, only the effect of extremely dense areas on the simulation can be taken into account and the transitions between areas with low and high Density can be sharpened.

Density Time Scale[0..10000%]

This value is used as a multiplier for the simulation time. Values below 100% slow down the time used for the Density calculation, values above 100% speed up the simulation time for the Density (see also the following figure).


All three images show the same simulation and the same simulation frame. Only the value for Density Time Scale was varied. 10% was used on the left, 100% in the middle and 1000% on the right. The Temperature simulation is unchanged in all three images.

Color

The settings in this group relate exclusively to the Color properties of the simulation. For example, decreases can also be used here to make the colors assigned to the Density fade over time or to influence the mixing of different colors.

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Color Mode

Various modes are available for calculating color mixtures within a simulation:


Two differently colored smoke simulations are mixed here: the Legacy mode on the left, the Simple mode in the middle and the Perceived Luminance mode on the right.

Relative Color Dissipation[0..100%]

This parameter describes the percentage reduction of the colour values per frame of the simulation, normalized to an image rate of 30. If the Density is visible long enough, it is darkened to black.


The series of images demonstrates the effect of increasing Relative Color Dissipation, causing the yellowish Density to darken to black over time.

Absolute Color Dissipation[0.00..1000.00]

This parameter describes the absolute dissipation of the color values per second of the simulation. This value is therefore selected rather small in many cases, as it refers to the value space between 0.0 and 1.0 of the RGB color components. The absolute change of the individual color components can also lead to color changes if a color component of the original color is much larger than the other components, for example. The following figure gives an example of this. As with the Relative Color Dissipation, the color of the Density is darkened to black if the Density remains visible long enough.


The series of images demonstrates the effect of increasing Absolute Color Dissipation. From left to right, the values 0.0, 0.25 and 0.5 were used. The yellowish Density here also passes through red hues before darkening to black.

As can be seen in the above illustration on the left, the RGB values 255, 166, 0 were used for the Density in the Pyro Tag. When using an Absolute Color Dissipation of 0.5, these values are reduced by 128 per second (1.0 corresponds to an RGB value of 255). This means that after one second, a Color value of 128, 38.0 is reached, which corresponds to a dark red tone. If you do not want the color decrease to change the color tone, you can alternatively use the Relative Color Dissipation.

Color Smooth Factor[0..100%]

Within the simulation, different colors can also be assigned for the Density, which then mix automatically. For example, a Vertex Color Tag can be used to assign different colors to an emitter object, or the differently colored Density of different Pyro emitters can overlap, as shown in the following figure. As can be seen there, the color transitions become blurred as the Color Smooth Factor increases.


Here, two separate cuboids are used as Pyro emitters. The lower cuboid emits red smoke, the upper cuboid green smoke. Yellowish mixed colors are created where the smoke plumes intersect. The transitions between all colors can be influenced with the Color Smooth Factor. A value of 0% was used on the left and a value of 100% on the right.

Color Time Scale[0..10000%]

This value is used as a multiplier for the simulation time. Values below 100% slow down the time used for the Color calculation, values above 100% speed up the simulation time for the Color.

Temperature

Here you will find settings that can be used to influence the change in Temperatures within the simulation, e.g. to speed up, slow down or completely deactivate the cooling of a hot gas.


Relative Temperature Dissipation[0..100%]

This parameter describes the percentage reduction in temperatures per frame of the simulation, normalized to a frame rate of 30.

Absolute Temperature Dissipation[0.00..10000.00]

This parameter describes the absolute reduction in temperatures per second of the simulation. The effect on the transitions within the temperature curves is comparable to that of the Absolute Ddensity Dissipation.

Temperature Smooth Factor[0..100%]

Temperature differences between neighboring areas are thus balanced out in the simulation, causing the temperature curves to lose detail and become more uniform.


All images show the same simulation but with increasing values for the smoothing of the temperatures, from left to right.

Temperature Active Threshold[0.01..+∞]

Only if the Temperature corresponds to at least this value specified in degrees will the simulation extend around the corresponding voxel. The effect of this setting on the simulation is often rather moderate. The effect of the following parameter for the Temperature Cutoff, on the other hand, is more obvious.

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Temperature Cutoff[0.01..+∞]

Information about temperatures below this degree value is deleted within the simulation. For example, by increasing this value, only the effect of extremely hot areas on the simulation can be taken into account and the transitions between hot and cooler areas can be sharpened. In addition, increasing this value can improve the visibility of the Density in the hotter areas.


On the left, the Temperature Active Threshold and Temperature Cutoff were each left at 1. In the middle, only the Temperature Active Threshold was increased to 700, on the right only the Temperature Cutoff was increased to 700.

Ambient Temperature[0.00..+∞]

You can use this to set the ambient temperature for your simulation. This can fundamentally change the course of the simulation, because a simulation that is cooler than the environment will sink downwards, for example, whereas a simulation that is warmer than the environment will generally rise upwards. This effect can also be amplified or reversed using the buoyancy values, e.g. for Density or Temperature.
The following simulation shows an example of this. Here, Density with a Temperature of 500 degrees initially rises upwards and cools down in the process. The Ambient Temperature was set to 40 degrees. This means that the haze that cools down below 40 degrees then also falls back down again.


Temperature Time Scale[0..10000%]

This value is used as a multiplier for the simulation time. Values below 100% slow down the time used for the Temperature calculation, values above 100% speed up the simulation time for the Temperature.

Fuel

Here you will find settings that can be used to limit the amount of Fuel in the simulation. This effect is usually less obvious compared to the comparable settings for Density, Color or Temperature, as Fuel usually does not remain in the simulation for long, but is often burned promptly, i.e. converted to Density, Temperature and Pressure.


Relative Fuel Dissipation[0..100%]

This value describes the percentage reduction in Fuel per frame of the simulation, normalized to a frame rate of 30.

Absolute Fuel Dissipation[0.00..1000.00]

This parameter describes the absolute reduction of Fuel per second of the simulation. This only refers to the unburned Fuel. By default, the value 0 is used so that there can be no reduction of unburned Fuel.

Fuel Smooth Factor[0..100%]

As the values increase, the Fuel is distributed more homogeneously.

Fuel Active Threshold[0.00..+∞]

Only the areas in which more Fuel is available than specified here at the threshold value are taken into account in the simulation. This setting can therefore be used sensibly to improve the simulation speed and also the memory requirement without losing important details. You will also find similar threshold values for Density and Temperature.

Fuel Cutoff[0.00..+∞]

Information about the Fuel whose quantity is below this value is deleted within the simulation. For example, if this value is increased, only the effect of extremely dense Fuel areas on the simulation can be taken into account.

Fuel Time Scale[0..10000%]

This value is used as a multiplier for the simulation time. Values below 100% slow down the time used for the Fuel calculation, values above 100% speed up the simulation time for the Fuel.

Velocity

These settings influence the flow velocities within the simulation and can therefore be used in a similar way to the damping of a soft or rigid body simulation. This means that kinetic energy can be extracted from the simulation system, e.g. to limit the overall size of a simulation, without having to change other physical properties such as buoyancy or temperatures.


Velocity Damping[0..100%]

This parameter can be used to reduce the movement speeds within the simulation. The higher the value, the more the movements are slowed down. If the Uniform Velocity Damping option is switched off, the reduction of the velocities can be specified here separately for each spatial direction. Otherwise, the velocities are influenced evenly.


On the left is the result of a simulation without Velocity Damping as a reference. In the middle, the vector 0%, 10%, 0% was used, whereby only the vertical movement of the explosion was damped. In the figure on the right, the effect was reversed by using 10%, 0%, 10%. Only the vertical direction of movement remains unaffected there.


The use of a time-varying damping also offers a further possibility to add irregularities and details to a cloud, for example. On the left, the original simulation without the influence of damping can be seen again as a reference. In the images on the right, an XPresso setup was used to use a variable variation of the damping vector via Noise nodes. Although the simulation becomes smaller overall due to the damping, it also obtains more details in the cloud structure.

Uniform Velocity Damping

When activated, the Velocity Damping is used evenly along all three spatial directions and thus slows down the speeds evenly. When switched off, this option ensures that individual velocity damping can be specified for the X, Y and Z directions.

Velocity Smooth Factor[0..100%]

With increasing values, different amounts and directions in the flow velocity of the simulation are compensated. This can be helpful, for example, when displaying fast-moving gases to make them appear blurred by motion blur.


The series of images, viewed from left to right, demonstrates the effect of increasing values for the velocity smoothing factor in a simulated explosion.

Velocity Threshold[0..+∞%]

To add new voxels to the simulation tree, the velocities of the simulation in the neighbouring cells are evaluated. With this limit value, you define the distance per simulation cycle that the gas must travel within a simulation cell in order to add new simulation cells at the edge of this cell. This value refers to the size of the cells in the tree as a percentage. Velocities in larger cells must therefore automatically be greater than in small cells in order to be taken into account.

Advanced Settings

Here you will find settings that can be used to configure and influence the calculation methods, for example. These settings are intended for advanced users and can fundamentally change the way the simulation works and looks.


Floating-point Precision

Here you can set the calculation precision within the simulation voxel. You can choose between 16-bit and 32-bit accuracy. Increasing the bit depth can lead to a more precise calculation of the simulation, which is also visible in the development of the shapes, as the following image shows.


Both explosions use the exact same settings on the Pyro tag and the Pyro Output object and show the same animation frame. On the left, the calculation was performed with 16-bit precision, on the right with 32-bit precision. In this example, the higher bit depth leads to more symmetrical and harmonious shapes of the rising cloud.

In general, it must also be decided on a case-by-case basis whether the higher bit depth is required, because it is also associated with increased memory requirements and longer simulation times.

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Out-of-Core Storage

This option can be used to extend the memory for voxel data on your graphics card that can be used by Pyro. The memory of your graphics card minus 1 GB, multiplied by a factor of 0.85, defines the upper limit for Pyro simulation data (0.85*(GPU memory-1GB)). This memory calculation is intended to ensure that as much, but not all, of the GPU memory is used for voxel data, as the other simulations and e.g. the 3D views also require memory. Activate this option to enable prioritization of GPU memory management for Pyro data.

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Smooth Factor around Colliders[0..100%]

Smooth Factor into Colliders[0..100%]

These values can be used to additionally smooth the grid structure for evaluation by collision objects. Smooth Factor around Colliders controls the smoothing of movements along a surface marked for collisions, whereas Smooth Factor into Colliders has a stronger effect on the simulation components that are on a collision course with collider objects. In both cases, however, increasing the value can also lead to simulation components penetrating the collider object at certain points. The following figure shows an example of this.

You can see a detailed view of a cone used as a collider object, which is hit by smoke from below. If both smoothing factors remain at 0%, precise collision detection corresponding to the selected Sample Size takes place. As known from renderings, this results in the typical staircase structures in the collision area. If Smooth Factor around Colliders is increased, smoothing takes place on the edges of the colliding Pyro structures, as can be seen in the middle illustration. Finally, if Smooth Factor into Colliders is increased, the simulation is also smoothed where it collides with the collider object (here especially at the tip of the cone in the right part of the following illustration).


From below, black smoke hits a cone tip, which is used as a collider object. On the left, both smoothing factors were used with 0%, in the middle, the smoothing around the collider was increased to 100% (Smooth Factor around Colliders) and on the right, the smoothing on collider objects was also increased to 100%(Smooth Factor into Colliders). The effect is particularly clear at the tip of the cone.

Staggered Velocities

This option influences how velocities are calculated in the simulated cells. When switched off, only velocities within the cell are evaluated. When this option is activated, the adjacent areas of a simulation cell are also included. This allows the pressure distribution to be calculated in more detail, which can have a positive effect on the quality of the entire simulation.

Note:Enabling this option also improves the interaction between the Pyro simulation and moving collider objects.


Both images show the same explosion, on the left without and on the right with Staggered Velocities.

Advection Reflection

Here you can select the precision of energy conservation within highly turbulent or fast simulations. Using the options First Order or Second Order leads to an increased memory requirement and slightly longer simulation time. As can be seen in the following figure, the higher orders lead to more visible turbulence and - due to the increase in Substeps associated with higher orders - to a reduction in the simulation volume.


Off mode on the left, First Order in the middle and Second Order on the right.

Advection

These parameters describe how components of the simulation behave in the flow of gases. For example, the unburned Fuel can be entrained by the gases, which can lead to a larger explosion during delayed ignition. In addition, various calculation methods are available for the simulation.


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Trace Integration

These settings change the sampling of the velocity structures within the simulation, which are then used for the movements of Density and Temperatures. The precision of the calculation increases according to the order of the options Euler, Runge Kutta 2 and Runge Kutta 4. The differences are particularly visible in fast-flowing simulations.


Euler Trace Integration on the left, Runge Kutta 2 in the middle and Runge Kutta 4 on the right.

Interpolation Accuracy

This setting controls the accuracy of the advection interpolation. The Cubic setting is much more accurate than Linear, which leads to a sharpening and generally to a higher accuracy, but also to simulation times that are approximately twice as long. The following figure gives an example of this.


Here, fast smoke flows from below onto a ring and collides with it. Linear interpolation is used on the left, Cubic interpolation on the right. The differences can be clearly seen here, especially in the lower part of the simulations.

Pre-advect Quantities

This option influences the sequence of calculations at the emitter:

By placing the simulation of scalar properties at the end of the calculation chain, this can lead to a reduction in artifacts.


Here, individual particles are generated at base emitters every second. Their Particle Groups are used as Pyro emitters. On the left, the Pre-advect Quantities option was switched off, on the right it was switched on. This improves the level of detail of the simulation on the particles in this example.

Advect Fuel

By activating this option, the Fuel that has not yet been ignited is carried along by the passing gas and will be distributed further in the simulation, if necessary.


Both images show the same simulation of an explosion, on the left without and on the right with Fuel Advection. Due to the relatively slow outflow of Fuel, the simulation results do not differ greatly from each other.


The simulation results change more strongly when Fuel is released suddenly, as in this example. Here, the Fuel Type Frame Range was used to generate the Fuel. The upper image sequence shows simulation phases without Fuel Advection. The option was activated for the lower image series.

Advection Mode

Various methods are available for the flow calculation. This can change not only the results, but also the time required for the simulation. The following image provides an insight into the differences between the available modes.


On the left is a simulation with SemiLagrangian, in the middle with MacCormack and on the right with BFECC.


Use Advection Mode for Velocity

If active, the method selected under Advection Mode is also used to simulate the velocities. Otherwise, the Semi-Lagrangian method is used by default.


The top images show simulations in BFECC mode with the Use Advection Mode for Velocity option enabled. The bottom images show the same simulations, this time with that option disabled. The differences are most obvious at the edges of the simulation.

Clamp Advection Result

This option is only available in the MacCormack or BFECC Advection Modes and, when activated, leads to the same simulation results of previous Pyro versions. This ensures that the interpolation results of a cell under consideration are within the value range of the surrounding voxels.
When switched off, this check is omitted, which can also lead to velocity peaks for individual voxel cells, for example. This can lead to slightly more variation in the simulation, as the following images also show.


The left column shows a simulation with the Advection Mode MacCormack, the right one a simulation with BFECC. The images in the upper row have no clamping activated, the lower ones are clamped in the advection result.

Correction Strength[0.00..3.00]

This can be used to adjust the sharpness and detail density of the simulation in MacCormack Advection Mode. Although the sharpness of detail increases at higher values, this can also lead to artefacts.


The series of images on the left begins with a correction value of 0. This value was increased by 0.5 in each of the following images. Increasing the value here leads to more detail, but also to a reduction in the size of the simulation.

Pressure Solver

In this section you will find parameters that can be used to influence the simulation of pressure changes. This is particularly interesting when using Fuel that can generate Pressure in addition to Density and Temperature.


Pressure Solver

Here you can choose between various complex algorithms for simulating the pressure distributions. The following series of images compares these modes as examples.


All images show the same simulation of an explosion, only different solvers were used to calculate the pressures.

The comparison between the relatively smooth curve of the Gauss-Seidel simulation and the Preconditioned Conjugate Gradient is particularly clear here, where there is a greater range of variation in the pressure distribution. Note also that the Preconditioned Conjugate Gradient is also based on the Multigrid V-Cycle.

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Solver Iterations[1..32]

This can be used to influence the calculation accuracy of the selected Pressure Solver. Older Cinema 4D versions did not offer this setting and generated results that correspond to a Solver Iteration of 1. Increasing the value usually leads to a more accurate evaluation of the simulation properties. As can be seen in the following image sequence, increasing the iterations not only leads to more details, but also to a greater expansion of the simulation in the direction of buoyancy.


Here you can always see the same simulation frame of an explosion. In the top row, the Solver Multigrid Full-Cycle was used and in the row below the Solver Preconditioned Conjugate Gradient. From left to right, the solver iterations 1 to 5 were used in each row.

Polish Iterations[0..256]

This can be used to control the computational accuracy and can be used to refine the simulation results in the Multigrid and Preconditioned Conjugate Gradient modes. In the Multigrid simulations (Preconditioned Conjugate Gradient is based on Multigrid V-Cycle as well), the simulation is first considered in coarse blocks and sections, which are then subdivided more and more finely for the following iteration steps. The number of these subdivisions is specified by the value for Maximum Multigrid Depth.


These images show an explosion with Preconditioned Conjugate Gradient. From left to right, the values 1, 2, 3, 5 and 7 were used for Polish Iterations.

Smoothing Iterations[0..256]

This value controls the iteration depth for the Multigrid part of the simulation. Since the Preconditioned Conjugate Gradient mode is also based on the Multigrid V-Cycle, this parameter is also used there. All iteration steps except for the first are affected by this. The iterations of the coarsest subdivision stage are determined by the value for Smoothing Iterations Final.


These images show an explosion with Preconditioned Conjugate Gradient. From left to right, the values 0,1, 2, 4, and 8 were used for the Smoothing Iterations.

Smoothing Iterations Final[0..256]

If you are using Gauss-Seidel, this sets the total number of calculation iterations. For the other modes, this sets the calculation depth of the coarsest subdivision level.


The series of images always shows the same simulation frame of a Gauss-Seidel calculation and starts on the left with a Smoothing Iterations Final value of 10. The following images on the right show the result of increasing this value by 10.


The series of images always shows the same simulated frame of a Preconditioned Conjugate Gradient calculation and starts on the left with a Smoothing Iterations Final value of 10. The following images on the right show the result of increasing this value by 10 in each case.

Maximum Multigrid Depth[0..6]

Here you specify the number of subdivision levels for the modes that use Multigrids (this also includes the Preconditioned Conjugate Gradient mode). More subdivision levels result in higher accuracy, but also in longer simulation times. However, it can also happen that the differences between the higher levels become so small that they can be neglected.
Note that the subdivision depth is automatically limited by the subdivision density of the voxel tree.


The series of images always shows the same simulation frame of a Preconditioned Conjugate Gradient calculation and uses (from left to right) the Multigrid Depth values 0, 2, 4 and 6. It is clear that the changes are always smaller at higher settings.


The series of images always shows the same simulation frame of a Multigrid Full-Cycle calculation and uses (from left to right) the Multigrid Depth values 0, 2, 4 and 6.


Initial Volume Override

These settings can be used in a similar way to the Initial Volume Set to define the initial state of the simulation. Explanations can be found further up on this page. However, the fact that not only a Volume Set object can be linked here, but also Volume Objects with the individual properties of a simulation, means that interesting combinations can also be implemented. For example, it is no problem to use the Colors, Temperatures, Density or Velocities of different simulations and combine them here as a new initial state. In addition, properties can also be swapped, provided their data types are identical.
Information on the Volume Set object can be found here and information on the Volume Object can be found here.


Initial Density

Link to a Volume Object that describes the Density at the start of the simulation. Floating point values are expected, so the Temperature orFuel can also be used here in addition to the Density. Volume Objects can be created via a Volume Set object (see Set Initial State button).

Initial Color

Link to a Volume Object that describes the colors within the Density at the start of the simulation. Vectors are expected, so theoretically the speed (Velocity) can also be used here in addition to the Color. Volume Objects can be created via a Volume Set object (see Set Initial State button).

Initial Temperature

Link to a Volume Bbject that describes the Temperatures at the start of the simulation. Floating point values are expected, so the Density orFuel can be used here in addition to the Temperature. Volume Objects can be created via a Volume Set object (see Set Initial State button).

Initial Fuel

Link to a Volume Object that describes the quantity and distribution of Fuel at the start of the simulation. Floating point values are expected, so the Density or Temperature can also be used here in addition to the Fuel. Volume Objects can be created via a Volume Set object (see Set Initial State button).

Initial Velocity

Link to a Volume Object that describes the Velocities within the simulation at the start of the simulation. Vectors are expected, so the color information of the Density (Color) can theoretically also be used here in addition to the Velocity. Volume Objects can be created via a Volume Set object (see Set Initial State button).


For example, colors and velocities are both vectors and can therefore be used for both Initial Color and Initial Velocity. The Density, Temperature and Fuel are all stored as floating point values and can therefore also be interchanged and used for Initial Density, Initial Temperature and Initial Fuel.
For example, a Temperature can also control the Density. This may not always be useful, but it encourages experimentation and in some cases can lead to appealing results that would be difficult to achieve in other ways.

The links offered here must be made to Volume Objects that refer to the respective property of a Pyro simulation. The easiest way to do this is to first create the desired state of a simulation as a Initial Volume Set. To do this, use the Set Initial State button in the Pyro Simulation Scene Settings.


On the left you can see an example of a Volume Set object with the simulation channels it contains for Color, Density, Temperature and Velocity. On the right you can see the Color information of the simulation extracted as a Volume Object.

In the illustration above, you can see how individual properties (in this case the 'color' component) can be extracted from a saved Volume Set object as a new Volume Object using the Detach button. These objects can then be used for Initial Volume Override. A small example of this is shown in the following illustrations.


On the left you can see the simulation frame for which a Volume Set object was created. In addition to the Velocity, it also contains the three properties for Color, Density and Temperature, which can be seen as individual Volume Objects on the right-hand side of the image.

As can be seen in the example above, colored smoke was first emitted from a sphere and a Volume Set object was created from which the components for Color, Density, Temperature and Velocity were then extracted. If, for example, a vertical plane is defined as the emitter and these properties are assigned to the sphere simulation as the Initial Volume Override, the result shown in the following figure is obtained. In the middle part of the plane, a change in Color occurs and the Temperatures, Density and Velocities of the sphere simulation influence the initial state of the plane there.

This sequence of images shows, from left to right, the initial state of the assigned sphere simulation and how it blends over time with the simulation of the plane

We would have obtained the same effect if we had assigned the Volume Set object directly as the Initial Volume Set. It is therefore more interesting to play with the assignments of the Volume Objects when doing the Initial Volume Override, as shown in the following illustration, for example.

Changed simulation after using 'density' as starting temperature and 'color' as starting color.

As can be seen in the figure above, a completely different result can also be achieved without much effort. Here, only the properties 'color' and 'density' of the original sphere simulation were used. As in the example above, the color is used as the Initial Color, but the density is used as the Initial Temperature. This is possible because the Temperature and Density are both based on floating point values and are therefore compatible with each other in the evaluation.
As can be seen in the figure, the Density of the sphere simulation leads to a heating of the Density in the middle of the plane. The Density rises and is colored with the Colors from the sphere simulation.

Draw

In this section, you will find the display options for the simulation in the viewports. This also includes additional information that can be helpful when optimizing the simulation.
Please note that the calculation of the rendering is not affected by these settings. The display of the simulated volume is then taken over by the Redshift Volume or Redshift Pyro Volume material and all light sources are also evaluated as usual.

In general, it should be noted that for a shaded and thus realistic preview of the Pyro simulation in the Viewports, either Constant Shading, Quick Shading or Gouraud Shading must be used (see Display menu of the Viewports).

In contrast to the display of normal objects, existing light sources in the scene are also evaluated in these modes for the Pyro display. Point Lights, regular Spot Lights and Infinite Lights are fully supported, as shown in the next illustration.

On the left is illumination by a Point Light source, in the center by a cone-shaped Spot, and on the right by an Infinite Light source.

The illumination by an Square Spot, a Parallel Spot, an Square Parallel Spot, an IES light source or a Redshift Dome light cannot be displayed. In these cases, the standard illumination is activated.
In addition, the illumination by an Area Light is displayed as with a Point Light source and a Parallel Spot or a Redshift Physical Sun appear as an Infinite Light source in their illumination.
The display of the illumination also supports the individual color of the light sources and their decay.


A colored spot with graduated falloff illuminates a Pyro simulation.

Draw Pyro

The simulation is only displayed in the editor views if this option is active. The prerequisite for this is that a shaded display quality is active in the respective view (Constant Shading, Quick Shading or Gouraud Shading). The options for Draw Bounding Box and Draw Tree Structure function independently of Draw Pyro.

Draw Bounding Box

The bounding box is drawn as the outer boundary of the simulation. This allows the position and size of a simulation to be estimated even if the simulation itself is not drawn, i.e. the Draw Pyro option is switched off.


The bounding box corners are highlighted in green where the Pyro simulation can be seen through a shaded display. The front view - shown here at the bottom right of the illustration - does not show any bounding box corners, as a Lines display is activated there.

Draw Tree Structure

This option can be used to draw the voxel tree, which is used to structure the simulation. These voxels are then further subdivided during the actual simulation, depending on the Voxel Count selected in the Tree Settings.
The size of this voxel structure is determined not only by the simulation itself, but also by the value for Padding, which serves as a kind of buffer in the edge area of the simulation, e.g. to track rapid gas movements and to be able to create or delete new voxels in good time.


Here, on the right side, you can see the representation of the Voxel tree on an explosion simulation.


Optimizing the simulation

Please note that there is currently a limit for the memory requirements of a simulation, which is 80% of the available graphics card memory. With very large or very detailed simulations, this can mean that no more new voxels can be created despite an expanding cloud. This is often made clear in the simulation by hard-cut areas, as can be seen on the far left in the next image.


On the left you see a simulated explosion. Due to the large spatial expansion and complexity, clipping occurs on the right side. The images in the center and on the right show two solutions to this problem.

In the simulation in the middle of the image above, the overall Density was reduced slightly by increasing the Density Active Threshold slightly. The simulation only changes the shape slightly as a result. Changes to the shading can be compensated for via material settings on the RS Volume material if necessary.

The image on the far right of the above figure shows a different solution. Here, the Padding was reduced in order to reduce the total number of voxels and thus also the memory requirements of the simulation. Although the shape changes there, the visual appearance of the explosion and its Density is retained.

Both solutions are therefore aimed at reducing the memory requirements of the simulation so that the simulation is not clipped. Other options could be to reduce the generated Temperatures or Pressures, as this also leads to a larger spatial expansion of the simulation and consequently to greater memory requirements. Higher values for the resolution of the Density and the cooling of the Temperatures can also be helpful (see Dissipation settings).

In addition, the total number of voxels can also be reduced by using larger voxels, which reduces the level of detail in the simulation somewhat, but if it is a large explosion or cloud, for example, the viewer will often be standing further away and therefore does not require such a high level of detail as a close-up.


On the left, hard steps and a clipping of the simulation at the right edge are visible, which are caused by missing voxels. On the right, the Voxel Size was increased only minimally from 5.1 cm to 5.5 cm. The simulation can now be calculated again without clipping problems.

Keep in mind that missing voxels in the simulation not only lead to an optical clipping, e.g. at one edge, but that the simulation as a whole can no longer work correctly. The Density values, Fuel concentrations, Temperatures, Pressures and Velocities of the omitted areas are missing in the overall calculation of the simulation and can therefore also have an effect on spatially more distant sections. This can also be seen in the image above. Although the Voxel Size was only minimally increased there to reduce the memory requirements of the simulation, the entire cloud shape changes. Therefore, always try to optimize the settings so that the entire simulation can be captured by voxels.

Another tool for limiting the number of voxels used is the Destructor force object, which can be found in the Simulate/Forces menu. It offers a special mode in conjunction with Pyro simulations. For example, only the voxels within the cuboid defined by the Destructor object are then used. If this option is used skilfully, the memory requirements of a Pyro simulation can be greatly reduced without any visible changes to the simulation. The following illustration gives an example of this.


If a Pyro simulation is combined with an Destructor force object, the simulation can be limited to the volume of the Destructor (see upper edge of the cloud). This function can be used to remove areas that are not relevant for the desired representation. This may save a lot of memory and simulation time.

Density Multiplier[0.00..100.00]

This value can be used to set the opacity of the simulated Density. For example, it is also possible to reduce it to 0 in order to only be able to view the flames or Temperatures. Please note that this setting only affects the display of the simulation in the editor view and has no effect on the rendering.


Here, as an example, increasing values for the Density Multiplier can be seen from left to right.

Draw Quality[0..100%]

Voxels are also used to display the simulation in the editor; small cubes that can be assigned colors and shaded by the incidence of light. The density and size of these voxels is controlled via this parameter. Here, too, there is no effect on the actual rendering of the simulation. Only the display in the viewports can be adjusted.


Here, the drawing quality increases gradually from left to right. It is particularly clear at the higher quality levels that this also improves the reproduction of the color nuances due to the temperature differences in the simulation (slight red coloration).

Emission Scale[0.00..100.00]

This allows you to adjust the brightness of the Temperature display in the editor.


Emission Scale values increasing from left to right.

Temperature Scale[0.00..100.00]

This setting relates to the Temperature values of the simulation. At higher values, cooler areas also become visible and start to glow. If you lower the value, however, the Temperatures in the simulation are lowered for the display. In extreme cases, this can mean that the Temperature can no longer be perceived as a flame at all. However, this only relates to the editor display. The Temperatures for the evaluation, e.g. by a Pyro Volume material, remain unchanged. Scaling options for interpreting the Temperatures are also available there for a similar effect.


From left to right increasing values for Temperature Scale.

Absorption Coefficient[0.00..100.00]

This parameter controls the light transmission of the Density in the editor view. As the absorption of light increases, the brightness of the Density display decreases and the contrast of the display increases. This setting also has no effect on the rendering of the simulation. The Redshift Volume material itself provides a parameter for controlling the absorption.


Here, the absorption increases gradually from left to right. At low values, the light can penetrate the simulation more easily and the cloud then looks like steam or dense fog, for example. At higher values, the contrast of the representation increases and the cloud appears more massive, such as a pyroclastic cloud above an erupting volcano.

Volume to Draw

You can use this menu to display certain properties of the simulation in isolation or also the shaded preview of the entire simulation. This setting also has no influence on the subsequent rendering of the simulation or the generation of the cache information.


From left to right, here are the representations of the Shaded volume, Density, Temperature, and Fuel, which is seen here only on the surface of the small cylinder used as an Emitter.


From left to right, here are the representations of Divergence, Velocities, and Pressures in the simulation.

Keep in mind that all display modes can also be affected by the Density Multiplier setting, e.g., to get finer gradations in temperature or pressures displayed.

Forces

The Pyro simulations can be influenced by Force Objects in the scene ( Simulate>Forces menu). If you only want to use certain force objects in the scene for the Pyro simulation, you can either include or exclude force objects here. Excluded forces then remain active for particles, for example, without affecting the Pyro simulations.


Note:If a Force Object is to be used simultaneously for all simulation systems (e.g. also for the clothing simulation), it must instead be entered in the Forces list under Simulation/Scene (in the Scene Settings or in the Simulation Scene Object). This is already done automatically in the Scene Settings when a new force object is added to a scene.

Mode

Here you select whether the force objects specified in the Objects list below should act on the simulation or not:

Objects

You can fill this list by dragging force objects from the Object Manager and apply them to your simulation according to the Mode setting. With the default Mode setting Exclude and an empty Objects list, all force objects compatible with Pyro apply to this simulation by default.