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Squidshire

Member Since 18 Jul 2012
Offline Last Active Aug 11 2012 11:48 AM

#4960473 Geometry shaders and depth FBOs

Posted by Squidshire on 18 July 2012 - 07:42 AM

Hi

Are there any special rules regarding rendering to an FBO when there's a geometry shader involved?

Context:
I'm trying to implement shadow mapping in a scene which includes different types of objects being rendered in different ways:
Meshes, rendered in the standard way through VBOs and shaders
Point sprite particles, rendered with a vertex and fragment shader
Quad particles, sent in as points but expanded to quads in a geometry shader

I'm doing shadow mapping in the standard way, which involves creating a depth FBO and rendering to it the object's depths from the light's point of view. The meshes and point sprites work fine, but the depths of the geometry shader quad particles aren't being rendered to the FBO.

Here's the standard (non-FBO) depth buffer. Note the large circular-shaped particles in the foreground.

Here's the same view rendered to the FBO. Note that only the depths of the meshes and point sprite particles are drawn.

My FBO is set up as follows (it's based on Chapter 7 from the OpenGL 4 Shading Language Cookbook):
const bool Renderer::generateShadowMap(FBO & f, string & error) {
  uint depthTexID;
  uint width = f.getWidth();
  uint height = f.getHeight();
  glGenTextures(1, &depthTexID);
  glBindTexture(GL_TEXTURE_2D, depthTexID);
  glTexImage2D( GL_TEXTURE_2D,  0,	 GL_DEPTH_COMPONENT,
  width,	height,	0,
  GL_DEPTH_COMPONENT, GL_FLOAT, NULL);
  float border[] = {1.0, 0.0, 0.0, 0.0};
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_BORDER);
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_BORDER);
  glTexParameterfv(GL_TEXTURE_2D, GL_TEXTURE_BORDER_COLOR, border);
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_COMPARE_MODE, GL_COMPARE_REF_TO_TEXTURE);
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_COMPARE_FUNC, GL_LESS);
  glActiveTexture(GL_TEXTURE1);
  glBindTexture(GL_TEXTURE_2D, depthTexID);
  uint fID;
  glGenFramebuffers(1, &fID);
  glBindFramebuffer(GL_FRAMEBUFFER, fID);
  glFramebufferTexture2D(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_TEXTURE_2D, depthTexID, 0);
  glDrawBuffer(GL_NONE);
  if(!checkFBOstatus(error)) {
	cerr << error << endl;
	   return false;
  }
  glClearDepth(1.0);
  glClear(GL_DEPTH_BUFFER_BIT);
  glBindFramebuffer(GL_FRAMEBUFFER, 0);
  glActiveTexture(GL_TEXTURE0);
  f.setFBOID(fID);
  f.setTexID(depthTexID);
  return true;
}

The shaders that should render the depths of the quad particles are:
//VERTEX SHADER
#version 400
in vec3 aPosition;
in float aSize;
out float gSize;
uniform mat4 vWorldView;
void main() {
  gSize = aSize;
  vec4 v4Vertex = vec4(aPosition.xyz, 1.0);
  vec4 transformedVertex = vWorldView * v4Vertex;
   gl_Position = transformedVertex;
}
//GEOMETRY SHADER
#version 400
layout (points) in;
layout (triangle_strip, max_vertices = 4) out;
in float gSize[1];
uniform mat4 vgProjection;
void main() {
  vec4 oPosition;

  float halfSize = gSize[0] * 0.5;
  oPosition = (vec4(-halfSize, -halfSize, 0.0, 0.0) + gl_in[0].gl_Position);
  gl_Position = vgProjection * oPosition;
  EmitVertex();

  oPosition = (vec4(halfSize, -halfSize, 0.0, 0.0) + gl_in[0].gl_Position);
  gl_Position = vgProjection * oPosition;
  EmitVertex();

  oPosition = (vec4(-halfSize, halfSize, 0.0, 0.0) + gl_in[0].gl_Position);
  gl_Position = vgProjection * oPosition;
  EmitVertex();

  oPosition = (vec4(halfSize, halfSize, 0.0, 0.0) + gl_in[0].gl_Position);
  gl_Position = vgProjection * oPosition;
  EmitVertex();
  EndPrimitive();
}
//FRAGMENT SHADER - empty as depth should be written automatically
#version 400
void main() {
}
Depth testing is enabled, of course. I've also tried telling the fragment shader to try to draw something to see if that makes a difference.

I've run this through gDebugger which can't detect any errors at all. I've tried telling the fragment shader to actually draw things but that doesn't make a difference either.

The only difference between the point sprite particles and the quad particles is the use of the geometry shader. I'm rendering both at the same time and with the same uniform values (and I've run gDebugger to make sure).

I've tested this on a computer with a nVidia GTX 560 Ti with driver version 8.17.13.142 (the latest, I believe, at the time of writing) and another with a Radeon Mobility HD 5650. I get the same result on both.

Am I making any obvious mistakes or are there some specific things I should know about?

Thanks


PARTNERS