Geometry shader with QT4.7

[saraksh]

QT4.7 on linux, video - nvidia 8600GT with latest driver and OpenGL 3.3 support.
Problem:
gl_DrawArray executes perfectly when I use vertex and fragment shader, but if I add a simple pass-thru(as I think) geometry shader - nothing is drawn on the screen. Geom shader source :
"#version 150\n"
"layout(points) in;\n"
"layout(points) out;\n"
"void main(void)\n"
"{\n"
"}\n"

shaders compiles without errors, shader program also links and run without errors.
In glsldevil debugger I'm getting INVALID_OPERATION detected after gl_DrawArray command when geom sh is enabled.

Thank U,

S

[stampede]

If I remember correctly, you have to emit some vertices from the geometry shaders,
so a pass-through geometry shader would be rather something like:

void main(){
  for(int i = 0; i < gl_VerticesIn; ++i){
    gl_Position = gl_PositionIn[i];
    EmitVertex();
  }
}

void main(){
  for(int i = 0; i < gl_VerticesIn; ++i){
    gl_Position = gl_PositionIn[i];
    EmitVertex();
  }
}

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Probably you'll have to set gl_FrontColor somehow as well, but I've coded shaders some time ago and cant remember all the details.

And about that:

"layout(points) in;\n"
"layout(points) out;\n"

Are you sure this syntax is correct ? What does it mean ?

Try to use my shader and see what happens (or just google for geometry shader tutorial, maybe look here also : http://nehe.gamedev.net/).

[saraksh]

"layout(points) in;\n"
	"layout(points) out;\n"

"layout(points) in;\n"
	"layout(points) out;\n"

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Are you sure this syntax is correct ? What does it mean ?

stampede, thank you for reply.
That's layout qualifier as per glsl ver 3.3.
Your suggestion didn't help.
I begin to suspect hw or sw bug: as per QFlags report: QFlags(0x1|0x2|0x4|0x8|0x10|0x20|0x40|0x1000|0x200 0|0x4000|0x8000)
I do have OpenGL 3.3 support(=0x8000), but after applying the very base format/context, query to majorVersion() minorVersion() (functions introduced in QT4.7) returns supported OpenGL version 1.0. So, continue googling.
Regards,

S

[przemo_li]

Hi!

Answer is very simple!

Geometry shader MUST emit vertexes that need to be passed to fragment shaders. If geom sh wont emit any vertexes, there will be nothing to pass to fragment shaders.

So basically your geometry shader is discarding all vertexes. OpenGL do not get any of them to assemble primitives and to divide them into fragments. So fragment shaders have no work to do. And now pixels on screen get updated. Use geometry shader that pass through all vertexes it get!

And pleas post your vertex and fragment shaders as well.