CODEWITHSUNDEEP
openglglslopentk
Andrew Tofelt
Andrew Tofelt

Reputation: 300

GLSL Passthrough Geometry Shader

I've been learning OpenGL (actually OpenTK) for a month or so, and I've started playing with geometry shaders. I originally wrote a much more complicated shader, which didn't work, so I've stripped everything down a simple passthrough shader, which still doesn't work.

Vertex Shader:

#version 420 core

layout (location = 0) in vec3 position;

uniform mat4 transform;

void main()
{
    gl_Position = transform * vec4(position, 1);
}

Geometry Shader:

#version 420 core

layout (triangles) in;
layout (triangle_strip) out;

void main()
{
    int i;
    for(i = 0; i < gl_in.length(); i++)
    {
        gl_Position = gl_in[i].gl_Position;

        EmitVertex();
    }

    EndPrimitive();
}

Fragment Shader:

#version 420 core

layout (binding = 0) uniform sampler2D diffuse;

layout(location = 0) out vec4 color;

void main()
{
    color = vec4(1, 1, 1, 1);
}

It should draw a white square in the bottom right of the window, and without the Geometry shader, it does, which is what I would expect. With the Geometry Shader, it renders nothing. Info logs show everything compiles and links fine.

What am I missing?

Upvotes: 3

Views: 994

Answers (1)

Paritosh Kulkarni
Paritosh Kulkarni

Reputation: 862

There must be a max_vertices declaration for the output. The number must be a compile-time constant, and it defines the maximum number of vertices that will be written by a single invocation of the GS. It may be no larger than the implementation-defined limit of MAX_GEOMETRY_OUTPUT_VERTICES

Upvotes: 2

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