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opengltessellation

Tessellation Shader - OpenGL

layout (vertices = 3) out;

void main(void)
{
    if (gl_InvocationID == 0)
    {
        gl_TessLevelInner[0] = 5.0;
        gl_TessLevelOuter[0] = 5.0;
        gl_TessLevelOuter[1] = 5.0;
        gl_TessLevelOuter[2] = 5.0;
    }
    gl_out[gl_InvocationID].gl_Position = gl_in[gl_InvocationID].gl_Position;
}

Excerpt From: Haemel, Nicholas. “OpenGL SuperBible":

How can I understand TessLevelInner and TessLevelOuter and why is the id 0 listed two times?

Solution

  • How can I understand gl_TessLevelInner and gl_TessLevelOuter?

    Please see: gl_TessLevelInner, gl_TessLevelOuter, OpenGL Tessellation - Levels

    As their names imply, they control the inner and outer tessellation factor levels for the primitive being processed. Below is an image illustrating the results of various inner/outer level settings.

    enter image description here Source: http://antongerdelan.net/opengl/tessellation.html

    Why is the index 0 used twice?

    It is used twice because it is accessing two different objects. The first use of index 0 is with

    gl_TessLevelInner[0]

    and the second is

    gl_TessLevelOuter[0]