Hi all!

I am trying to use the NV_explicit_multisample extension with GLSL. But i can’t figure out how to use the renderbuffer texture in my fragment shader.

What I do is rendering my scene to the multisample renderbuffer in the first pass. In a second pass I want to read from the generated renderbuffer texture to get each sample for a fragment.
First pass works fine, if i blit the framebuffer object and have it displayed its working. But how can i set up the uniform samplerRenderbuffer to use the texelFetchRenderbuffer function in my fragment shader?

This is how i set up my framebuffer object for rendering the renderbuffer texture (i skipped the depth buffer here):

glGenTextures(1, &multisampleDepthPeels);
glBindTexture(GL_TEXTURE_RENDERBUFFER_NV, multisampleDepthPeels);
glGenRenderbuffersEXT(1, &rbDP);
glBindRenderbufferEXT(GL_RENDERBUFFER_EXT, rbDP);
glRenderbufferStorageMultisampleCoverageNV( GL_RENDERBUFFER_EXT, 16, 4, GL_RGBA32F_ARB, _resx, _resy);
glGenFramebuffersEXT(1, &fbDP);
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fbDP);

And after rendering my scene i try this to use the renderbuffer texture:

glBindTexture(GL_TEXTURE_RENDERBUFFER_NV, multisampleDepthPeels);
glUniform1i(glGetUniformLocation(techTestProgram, "resx"), _resx);
glUniform1i(glGetUniformLocation(techTestProgram, "resy"), _resy);
glUniform1i(glGetUniformLocation(techTestProgram,"multisampler"), 1);
////render to FrameBufferObject
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fb);
glDrawBuffers(1, sRT);

with this fragment shader:

#version 120
#extension GL_EXT_gpu_shader4 : enable
#extension GL_NV_explicit_multisample : enable

uniform int resx, resy;
uniform samplerRenderbuffer multisampler;

void main(void)
  ivec2 curr_pos =  textureSizeRenderbuffer(multisampler) - ivec2(resx,resy);
  gl_FragData[0] = texelFetchRenderbuffer(multisampler, curr_pos, 0);

which doesnt work.
If i use

glBindFramebufferEXT( GL_DRAW_FRAMEBUFFER_EXT, fb);
glBlitFramebufferEXT( 0, 0, _resx, _resy, 0, 0, _resx, _resy, GL_COLOR_BUFFER_BIT, GL_NEAREST);

and render a quad with the 2d texture bound to fb it works, but of course i have no access to each individual sample anymore.

Maybe someone tried to use NV_explicit_multisample and can give me a hint or point me towards a code example/ documentation thats a little more descriptive other than the extension specification. Any help is much appreciated!

What do you mean by it doesn’t work?

Your code looks ok.

From what I understand, it looks like you are trying to fetch the sample 0 for the texel at texcoord (textureSizeRenderbuffer(multisampler) - ivec2(resx,resy))

I mean nothing is drawn in the second pass, screen is filled with the clearColor.
And yes, i try to fetch the sample 0 from the texture renderbuffer, to test the basic functionality.

edit: Solved, didnt read from the correct texel coords.

texelFetchRenderbuffer(multisampler, ivec2(gl_FragCoord.xy), 0);

works as intended.