I'm having a hard time getting OpenGL Tessellation to work. I have been struggling with it for about a month now. I've looked at a lot of example code and what I am doing doesn't seem that different to what they are doing in their code. I was wondering if anyone could be a second pair of eyes and maybe point out why it isn't working.

My scene is only rendering a black screen.

My shaders are as follows:

Vertex Shader

#version 400
#extension GL_ARB_tessellation_shader: enable
#extension GL_ARB_separate_shader_objects: enable

layout(location = 0) in vec3 vertexPosition;

void main()
{
    gl_Position = vec4(vertexPosition, 1.0);
}

Tessellation Control Shader

#version 400
#extension GL_ARB_separate_shader_objects: enable

layout(vertices = 3) out;

void main()
{
    float inLevel = 2;
    float outLevel = 2;
    
    gl_out[gl_InvocationID].gl_Position = gl_in[gl_InvocationID].gl_Position;
    
    if (gl_InvocationID == 0)
    {
        gl_TessLevelOuter[0] = outLevel;
        gl_TessLevelOuter[1] = outLevel;
        gl_TessLevelOuter[2] = outLevel;
        gl_TessLevelOuter[3] = outLevel;

        gl_TessLevelInner[0] = inLevel;
        gl_TessLevelInner[1] = inLevel;
    }
}

Tessellation Eval Shader

#version 400
#extension GL_ARB_tessellation_shader: enable
#extension GL_ARB_separate_shader_objects: enable

layout(triangles, equal_spacing, ccw) in;

uniform mat4 uMVPMatrix;

void main()
{
    vec4 p0 = gl_TessCoord.x * gl_in[0].gl_Position;
    vec4 p1 = gl_TessCoord.y * gl_in[1].gl_Position;
    vec4 p2 = gl_TessCoord.z * gl_in[2].gl_Position;

    vec4 newCoord = normalize(p0 + p1 + p2);
    gl_Position = newCoord;
}

Geometry Shader

#version 400
#extension GL_ARB_separate_shader_objects: enable

layout(triangles) in;
layout(triangle_strip, max_vertices = 3) out;

uniform mat4 uMVPMatrix;

uniform bool UseWaveGeometry;
uniform float GameTime;

layout(location = 3) out vec4 vColor;

float rand(vec2 n)
{
    return 0.5 + 0.5 * fract(sin(dot(n.xy, vec2(12.9898, 78.233)))* 43758.5453);
}

void setUpValues(int index)
{
    vec4 vertPosit = gl_in[index].gl_Position;
    
    if(UseWaveGeometry)
    {
        vertPosit.y = vertPosit.y + (GameTime + ((cos(vertPosit.x)) * GameTime) - ((sin(vertPosit.x))*GameTime)*2.2);
    }
    
    float cval = int(vertPosit.x) % 2 + int(vertPosit.y)%2;
    vColor = vec4(cval, cval, cval, 1.0);

    gl_Position = uMVPMatrix * vertPosit;
}

void main()
{
    for(int i = 0; i < 3; i++)
    {
        setUpValues(i);
        EmitVertex();
    }
    EndPrimitive();
}

Fragment Shader

#version 400
#extension GL_EXT_gpu_shader4: enable
#extension GL_ARB_separate_shader_objects: enable

uniform float ColorAlpha;

layout(location = 3) in vec4 vColor;

layout(location = 0) out vec4 FragColor;

void main()
{
    vec4 color = vec4(vColor.r, vColor.g, vColor.b, ColorAlpha);
    
    FragColor = color;
}

Thank you for your time,
Marty

Thank you for the reply. Sorry for the late response. I read your message a few days ago.

The reason I didn't use the layout location identifiers is that I am dynamically getting the location in my C code by the name of the attribute. I also keep my variables named the same. Although it would make for easier to understand shader code if I used them as well. That way users can see at a glance what output matches up with what input.

I will implemented this and post my results.

Thank you very much for the feedback. It is greatly appreciated.

Edit

--------------------------------------------

I modified my previous post with the updated shaders. I still get the same issues with tessellation.

Anyone have any idea? Anything at all I could try? Any feedback would be greatly appreciated.

Edit:

---------------------------

I simplefied the code. I still get a black screen when the tessellation shaders are enabled. It renders a scene with them commented out.

I have been using that reference as a tessellation example.

The biggest problem is that my code base is so huge. I have texture arrays for height maps, FBO for shaows, reflections, and a bunch of other stuff which complicate code slightly.

I will check out the AMD GPU shader analyzer. Thanks for the info. I will post an update when I test it

I finally figured out my issue.

It wasn't shaders at all. My problem with tessellation was that I was drawing my objects using GL_TRIANGLES. Tessellation only works on GL_PATCHES.