Cinema 4D / BodyPaint 3D Program Documentation Tutorials Mechanical Modeling Tutorial Modeling with Splines and Generator Objects
Function available in CINEMA 4D Prime, Visualize, Broadcast, Studio & BodyPaint 3D

Extrude Object

Objects such as a 3D logo or text basically consist of only an outline whose depth has been increased in order to define a volume for the given object. This is exactly what the Extrude object does (Create | Generator). If a Spline Object is made a Child object of this Extrude object, the Spline object’s shape will be thickened along a given axis. The axis, or axes, along which the Spline object will be extruded is defined by the Extrude object Movement values. These values represent the X, Y and Z axis, respectively (see image below).

The Extrude object can modify multiple Splines at once. Make sure the Hierarchical option is enabled when doing so. Each Child Spline will be extruded according to its own object axis (see image below).

Usually the extrusion is completed in a single step. If you want to increase the subdivision of the surfaces created, simply increase the Subdivision value in the Attribute Manager. Increasing the subdivision can, for example, be useful if further modifications of the object are planned. Increasing the subdivision will not affect the extruded surfaces’ shape.

Caps

Cap surfaces can be generated, with or without a rounded edge on Start and End of the object, in order to give an object a more substantial look. The image below shows examples caps surfaces. Note how segments are interpreted in the areas of closed curves (holes), especially around the eyes and mouth. These must however be segments of a single spline object: If multiple separate splines are extruded together using the Hierarchical option, the inner elements will not be recognized as holes.

Caps surfaces with rounded edges (Fillets)

In the Caps tab’s menu, the Start and End parameters offer several options from which to choose for modeling edge and caps of your extruded surface. The Start and End parameters’ Steps values define the Fillet’s subdivision, i.e., the curvature’s accuracy. The Radius values define the size of the Fillet, i.e., how large the curvature is. Furthermore, theFillet Type menu offers various options for shaping the edge of your extruded surface. Experiment a little with the settings to see what all they do. For example, combining a Convex Fillet Type with a Step value of 1 will result in a linear transition between edge and cap surface.

Maintaining the contour

A very important option that should be enabled when creating Fillets is the Constrain option. If this option is not enabled, the Fillet’s radius will be added to the extruded object’s total radius, thus altering the actual shape of the Extrude object. Adding the Fillet’s radius to the overall radius prevents Fillets from penetrating surfaces in tight curves but also changes the shape of the Spline. Since changing the Spline’s shape is generally not desired, enabling the Constrain option will maintain the Spline’s shape and prevent the radius from being increased. However, you may have to make sure that no surfaces are penetrated and reduce the Fillet size if necessary.

The image below shows the difference between an enabled and a disabled Constrain option. The example on the left has the Constrain option disabled. You can see how the eye and mouth openings were enlarged and the overall size of all objects was increased compared to the example on the right, for which the Constrain option was enabled. Enabling the Constrain option maintains the original Spline shape but can more easily lead to unwanted results with regard to the shape and cap surfaces. In the example on the right, for example, the area between the eye and the edge of the model is far too narrow. If the Radius value were increased any more, the surfaces would begin to intersect.

Subdividing cap surfaces

A wide variety of objects can be created using simple Spline curves in conjunction with Extrude objects, for example gears, I-beams, 3D text and logos, or even a room that can be created by simply extruding a floor plan outline. However, not all objects are created with cap surfaces that are well-suited for subsequent modification. The example on the left of the image below shows how the caps surfaces of our object would look if the Type option were set to N-gons. Normally, this setting would result in a caps surface consisting of only a single polygon, as is the case with the circles to the left and right of the head. However, if the Splines contain segments that are interpreted as holes, no N-gons can be generated. The Extrude object will then automatically create triangles - with the resulting chaotic structure. You can also set the Type option to Triangles or Quadrangles. Due to the holes in our model, this would only change the subdivision of the circles’ cap surfaces in our example, as is shown at the center of the image below. If the Generator object will subsequently be deformed, applying the N-gons, Triangles or Quadrangles modes is generally not a good idea because the polygons will be too short and will stretch across the entire surface. Since deformations only affect points, unwanted constrictions and shadow casting will occur.

Uniform cap surface subdivision

To solve this problem, the surface will have to be subdivided into surface with a uniform size. This is shown at the right of the image above. To achieve this type of subdivision, select either Dreiecke or Vierecke mode and enable the Regular Grid option. The only place irregularly-sized polygons are now generated is at the edges. These polygons are generally so small that they will not cause problems when the object is deformed. The newly-created points also let you deform the object locally, as shown in the image below. You can even twist or bend the entire Extrude object.

Since the aforementioned options can be applied to any caps surfaces on all Generator / Spline object combinations we will not reiterate them in the following.

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