Redshift Contour

The Contour shader draws lines around an object's silhouette and along prominent internal edges that define an objects shape. Redshift's line drawing is shading based so it works automatically with reflections, refractions, depth of field, and motion blur but it is confined to the inner bounds of an object. Technically, a contour can never render outside of an object's silhouette but a workaround can be used to achieve a similar visual effect as described in the Contour Behavior section below, Breaking Boundaries.

The Contour shader is one of three shaders that make up Redshift's core offering of non-photorealistic tools. The Toon Material is used as the primary shading element to create stylized cel shaded looks, the Contour shader is used to create outlines around your objects, and the Tonemap Pattern texture adds a screen space pattern to your shading to mimic a halftone dot effect and others.

Example Graph

Basic Setup

Thickness based on distance

To shrink contours as they fade into the distance a State node can be used. Create a State node and use the ray length output into a Change Range node. The ray length produces the distance from the camera to an intersected point so the Old Range should be set to the minimum and maximum distance in scene units while the New Range is set to the min and max values used for the Contour Thickness Modifier. For example, if the farthest part of your scene is 100 units away you should set the Old Range input from 100 min to 0 max and, if you want your contours to start at full width close to the camera and shrink down to half their size in the distance, set the New Range min to 0.5 and max to 1.

Contour Behavior

External vs Internal Lines

A scene can exhibit many different scenarios and understanding how contours behave in different conditions is important to getting the most out of them. To start with the basics, External Lines draw a line around the silhouette of an object while Internal Lines draw a silhouette and have the ability to draw lines along interior details of an object. Both types of lines can be used at the same time, however, external lines are always drawn on top of internal lines. In the examples below, external lines are black and internal lines are red, note how the red internal lines are still drawn around the silhouette of an object but they capture additional detail that external lines cannot. Line thickness and other settings have been exaggerated to make the differences readily apparent, thin lines are generally better for more small details.

However, if an internal line is thicker than an external line it will peek out from under the external lines. In the example below, the black external lines have a thickness of 10 and the red internal lines are animated from a thickness of 0 all the way up to 20. Around the half way point of the animation both lines have the same thickness, but as the thickness continues to climb the red internal lines can be seen next to the external lines along the silhouette of the object.

How your objects are constructed also has an impact on the appearance of contour lines. Since external lines only draw a line around the silhouette of an object, there can be a large difference between whether your objects are combined into a single mesh or made up of several smaller objects. In the example below, the robot model has been combined into a single mesh which completely changes where the black external lines are visible. By comparison, the red internal lines occupy the same general location but they are now uncovered in many areas.

Intersections and Overlaps

Contours can behave differently when other objects intersect with or render in front of an object with a contour, this is dependent on the Detect Separate Meshes parameter. By default, when set to "Off," overlapping and intersecting objects do not create contours.

However, when Detect Separate Meshes is set to "Overlapping and Intersecting," contours are drawn around the silhouette of overlapping objects and along any mesh intersections. Note that the contour does not draw on top of the overlapping or intersecting object — the blue spheres in the example below — the contour is only drawn on the object that has contours applied to it.

You can also isolate these effects from each other by using either the “Intersecting” or “Overlapping” modes. However, these modes are only approximations and do not guarantee that two objects actually intersect with each other. Scene scale has an impact on the accuracy of these modes, try increasing the scale of your objects or using the “Overlapping and Intersecting” mode for the most stable results.

Breaking Boundaries

Contours cannot be drawn outside the bounds of the objects that they are applied to, but it is possible to create a visual illusion that contours are rendered outside the bounds of an object. Since an object passing in front of an object with contours causes a line to be drawn, this can be leveraged to create a convincing effect that contours have no limits. Essentially, this requires all objects in a scene to use contours, and most importantly, that a background object uses contours so that the edges can be drawn anywhere outside the bounds of an object that appears in front of that background.

In the examples below, the foreground objects have red internal lines and black external lines, while the background cyke object has dark blue internal lines and light blue external lines.

With all the different colors, this can start to look like a bit of a visual mess — however, we can leverage this behavior and use it to our advantage to create very stylized looks. In general, this trick works best with contours that have the same color so the difference between foreground and background object contours cannot be distinguished. In the example below, all contours use the same Maxon noise texture to control the thickness modifier, allowing for variable width lines. In the first example, there is no way to distinguish between foreground or background contours resulting in the illusion that the lines are breaking out of the boundary of the foreground objects resulting in a very stylized effect. In the middle example, the background contours have been changed to red to demonstrate the difference. In the last example you can see how the scene looks if no background contours are used, the foreground contours are cleanly cut off along the silhouette of the objects.

Combined with a toon shader and a bump map to distort the tone mapping it is possible to bring all these elements together for different artistic looks.

Global Contours

Redshift offers two ways to control contours across your entire scene. These options can be found in the Render Setting's Global tab as pictured below.

The Contour Scale option scales the thickness of all contours in the scene as a multiplier value. For example, if you have two contours in your scene and one is set to a thickness of 3 and the other is set to 5, with the Contour Scale set to 2.5 the new thicknesses would be equivalent to 7.5 and 12.5.

The Default Contour feature lets you connect a material with a contour node that is applied to all objects in the scene. The Default Contour has no effect on materials that have their own contour setup at the local material level. The Default Contour is a great way to manage contours for background elements and then use more specialized contours for hero assets.

When using the Default Contour feature but you want a material to have no contours at all, connect a contour to that material and disable Internal and External contours manually.

Parameters

General

Visible in Reflection

Controls if contours are visible in reflections. Disabling Visible in Reflection stops contours from appearing in reflections, this includes self reflections.

In the examples below, a rough mirror is placed next to the toon objects. When disabled, contours cannot be seen in the mirror.


Visible in Reflections: Enabled (default)	Disabled

Visible in Refraction

Controls if contours are visible in refractions. Disabling Visible in Refraction stops contours from appearing in refractions, including self refractions.

In the examples below, a smudged transmissive window is placed in front of the toon objects. When Disabled, contours cannot be seen through the glass.


Visible in Refractions: Enabled (default)	Disabled

External

Tonemap

Controls the shading with an externally connected ramp or texture node, this is where you can give contours a shaded look. Using a ramp with stepped interpolation results in a classic cel shaded look where the transition between highlight and shadow is abrupt and sharp. The External Tonemap color is multiplied with the External Color — so the External Color must be brighter than black in order to see any shading effect.

Tone mapping works by mapping the light intensity on the objects in your scene (the illuminance) to a ramp node with colors and shading defined by you. With a horizontal ramp, the left side of the ramp controls the shadow color, the middle part of the ramp controls the midtone colors, and the right part of the ramp controls the highlight color.

Tone mapping on the Contour shader works exactly like the Base Tonemap on the Toon material. For more detailed information, please see the Toon Material page.

Ramp nodes are automatically used as a tonemap when they are connect to a Tonemap input.


Tonemap Input: Stepped Ramp	Colorful Ramp	Tonemap Pattern

Thickness

Controls the maximum thickness of the external lines. The Thickness parameter only accepts a constant value, to vary the thickness use the Thickness Modifier instead.

The thickness parameter is measured in pixels for a 1920x1080 resolution image, rendering in other resolutions rescales the thickness automatically so that it appears to have the same relative thickness at any resolution.

External lines will cover up Internal and Backfacing lines if they are thicker and occupy the same location.

The width of all contour lines in a scene can also be scaled with the Contour Scale option found in the Globals tab of the Render Settings.


External Line Thickness: 0	3	8	15

Thickness Modifier

Changes the width of the external lines, connect a texture here to vary the thickness along external lines. Lower values decrease the width of a line, with 0 resulting in no visible thickness, while higher values increase the width and a value of 1 results in full thickness. The maximum width of a line is always limited by the Thickness parameter, increase the overall thickness in order to give yourself more room for thickness variation.


Thickness Modifier: Maxon Noise with animated color	Animated Texture

Detect Separate Meshes

Controls if overlapping or intersecting meshes create contours for external lines from the following modes:

Off – Contours are not drawn around objects that intersect with or appear in front of an object with contours.
Intersecting – Contours are drawn around objects that intersect with an object with contours.
Overlapping – Contours are drawn around objects that appear in front of an object with contours.
Overlapping and Intersecting - Contours are drawn around objects that intersect with or appear in front of an object with contours.

The “Intersecting” and “Overlapping” modes are approximations and do not guarantee that two objects actually intersect with each other. Scene scale has an impact on the accuracy of these modes, try increasing the scale of your objects or using the “Overlapping and Intersecting” mode for the most stable results.

Contours only draw on the object with the contours applied, they cannot draw on top of the overlapping or intersecting objects unless they also have a contour shader applied to them.


Detect Separate Meshes: Off (default)	Intersecting	Overlapping	Overlapping and Intersecting

Internal