Creases

Realsoft Graphics Oy		Creases
	Chapter 3. Subdivision Surfaces

Creases allow you to create sharp edges for SDS surfaces.

Creases are similar to 'weights' in that they allow you to control how strongly a certain point, edge or face 'attracts' the actual surface.

Realsoft 3D supports three crease levels: sharp, semi sharp and rounded. In addition to this, there are two kinds of creases: point creases and edge creases.

Point creases are affected whenever you use the 'Sharpness' tool in the point editing mode. If you are in edge or face editing mode, edge creases are affected. This means that the result of setting creases for all points of a face is different from setting crease values for the edges of the face.

The four top points have a semi sharp crease value. The bottom vertices have the default smooth crease value.

The following tutorials demonstrate how different crease values and types affect the shape of the actual surface.

Point creases

You can define crease values for selected points using the 'Sharpness' SDS tool.

Sharpness tool in the control bar

A SDS cube with default crease values

1. Create a SDS Cube. By default all crease values are set to 'rounded' and the resulting surface looks like a sphere.

2. Enter the point editing mode and select all points of the SDS object. The 'Sharpness' control in the tool control bar becomes enabled.

3. Set sharpness to Semi Sharp.

The SDS cube with semi sharp point creases

A ray traced SDS cube with semi sharp point creases

	Note
	OpenGL shading can represent the true shape of a SDS surface only with a limited quality. In photo realistic rendering, creases become rendered with a proper quality.

If you set a point crease to sharp, you'll get a sharp peak, as shown in the image on the right.

Two points with a sharp crease

Edge creases

Edge creases are defined in edge or face editing modes. Defining a crease value for a face corresponds to defining a crease value for all edges of the face.

Let's see how edge creases differ from point creases.

1. Create a SDS cube just like in the previous example.

2. This time, enter the face mode and select the top and bottom faces.

3. Set crease to 'Sharp' using the sharpness tool.

The actual surface looks like a cylinder now.

A SDS cube with 'Sharp' top and bottom face creases

Mixing point and edge creases

Point and edge creases can be mixed.

The edge creases of the top and bottom faces are 'sharp'. All point creases are set to 'semi sharp'. Side edges are also semi sharp.

Note

If you apply tools which create new points or edges for SDS object, all inserted points will have a default 'smooth' crease value.

For example, if you subdivide and extrude the top face of the SDS object in the image above, the following object is the result:

Top face subdivided and extruded


Rational Subdivision Surfaces		Rounding