GLSL：将细分从曲面细分评估着色器移动到顶点着色器

Question

I am working in glsl with tessellation-shaders and I am trying to do displacement mapping. It's working, but I want to move the matrix-transformation-code from the tessellation evaluation shader to the vertex shader. Why I want to have this in the vertex-shader is because I do not want to do this calculation for every sub triangles vertices, and I want the vertices to be in screenspace in the vertex shader so I can decide how much every triangle should be subdivided in the tessellation control shader.

The version that do not work, is "almost" working, there is some issues when the triangles are rendered.

I would really appreciate even the smallest hint of what may be wrong.

---

This (bad) version works (position and normal are transformed in tessellation evaluation shader)

// vertex shader
void main_(void)
{
    gl_Position     = VertexPosition;
    VertexTexCoord1 = VertexTexCoord;
    VertexNormal1   = VertexNormal;
}

// tessellation evaluation shader
void main_()
{
    VertexTexCoord3     =    interpolate(VertexTexCoord2);
    vec3 normal         =    interpolate(VertexNormal2);
    vec4 pos            =    interpolate(gl_in[0].gl_Position, gl_in[1].gl_Position, gl_in[2].gl_Position);

    vec4 movement       =    vec4(normal * (texture2D(heigthMap,VertexTexCoord3).r), 0.0);

    gl_Position         =    mvpMatrix * (pos + movement);
}

---

This version does not work (position and normal are transformed in vertex shader)

// vertex shader
void main(void)
{
    gl_Position     = mvpMatrix * VertexPosition;
    VertexTexCoord1 = VertexTexCoord;
    VertexNormal1   = mat3(mvpMatrix) * VertexNormal;
}

// tessellation evaluation shader
void main()
{
    VertexTexCoord3     =    interpolate(VertexTexCoord2);
    vec3 normal         =    interpolate(VertexNormal2);
    vec4 pos            =    interpolate(gl_in[0].gl_Position, gl_in[1].gl_Position, gl_in[2].gl_Position);

    vec4 movement       =    vec4(normal * (texture2D(heigthMap,VertexTexCoord3).r), 0.0);

    gl_Position         =    (pos + movement);
}

Answer 1

In the "non-working" version the last line in tesselation shader seems to be incorrect. You're forgetting that in the source variant you had 'movement' multiplied by the mvpMatrix.

I would have tried to use this:

// tessellation evaluation shader
void main()
{
    VertexTexCoord3     =    interpolate(VertexTexCoord2);
    vec3 normal         =    interpolate(VertexNormal2);
    vec4 pos            =    interpolate(gl_in[0].gl_Position, gl_in[1].gl_Position, gl_in[2].gl_Position);

    vec4 movement       =    vec4(normal * (texture2D(heigthMap,VertexTexCoord3).r), 0.0);

    /// This multiplication by mvpMatrix is inevitable
    gl_Position         =    (pos + mvpMatrix * movement);
}

Sorry if I mixed the order of the stages, but the code above (two versions) is definitely non-equivalent.