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The dispstar shader is a very simple shader written in Open Shading Language (OSL).  It computes a displacement amount depending on radial angle in the x-y plane.  When applied to a spherical shape, it produces a round star with five soft spikes.  When applied to a teapot (with higher frequency), it produces a pumpkin-like shape.

shader
dispstar(float scale = 1.0, float freq = 5.0,
         output float resultF = 0.0)
{

...

   // Compute displacement amount

...

   float angle = atan2(N[1], N[0]);

...

   float disp = scale * sin(freq*angle);

...

   resultF = disp;
}

In this example, the displacement amount computed by dispstar gets passed on to the PxrDisplace displacement shader, which does the actual displacement.  Here is an image of a sphere and the same sphere with displacement (along with an image with holes due to too small displacement bound):

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