OpenGL texture blit via framebuffer not copying alpha

[FoxMcCloud]

I have a simple texture blit function in OpenGL that I'm trying to use to copy an RGBA16F texture to another one of 1/4 size:

void texture_blit(const GLuint SourceTexture, const int SourceX0, const int SourceY0, const int SourceX1, const int SourceY1, 
                  const GLuint DestinationTexture, const int DestinationX0, const int DestinationY0, const int DestinationX1, const int DestinationY1)
{
    GLint PreviousReadFramebuffer;
    GLint PreviousDrawFramebuffer;
    glGetIntegerv(GL_READ_FRAMEBUFFER_BINDING, &PreviousReadFramebuffer);
    glGetIntegerv(GL_DRAW_FRAMEBUFFER_BINDING, &PreviousDrawFramebuffer);
    using namespace application;
    glNamedFramebufferTexture2DEXT(BlitSourceFramebuffer, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, SourceTexture, 0);
    glNamedFramebufferTexture2DEXT(BlitSinkFramebuffer, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, DestinationTexture, 0);
    glBindFramebuffer(GL_READ_FRAMEBUFFER, BlitSourceFramebuffer);
    glBindFramebuffer(GL_DRAW_FRAMEBUFFER, BlitSinkFramebuffer);
    glBlitFramebuffer(SourceX0, SourceY0, SourceX1, SourceY1, 
                      DestinationX0, DestinationY0, DestinationX1, DestinationY1, 
                      GL_COLOR_BUFFER_BIT, GL_LINEAR);
    glBindFramebuffer(GL_READ_FRAMEBUFFER, PreviousReadFramebuffer);
    glBindFramebuffer(GL_DRAW_FRAMEBUFFER, PreviousDrawFramebuffer);
}

However, when I use that to copy between two RGBA16F textures Alpha seems to be discarded - the target texture's RGB is a copy of the destination's but the target's alpha is a constant 1. Am I doing something wrong or is this a driver issue?

 

[FoxMcCloud]

I uploaded pictures of the textures as seen in OpenGL Profiler to Flickr: http://www.flickr.com/photos/59098813@N06/sets/72157627929133639/

 

[homerdog]

What is your hardware?

http://www.atomicmpc.com.au/Feature...and-degrading-game-quality-says-nvidia.aspx/1

However, FP16 Demotion aims to change how HDR lighting is calculated; its full name is the R11G11B10 format, which means the Red and Green channels have 11 bits each, with Blue sitting at 10 bits for a total of 32 bits per pixel - dropping Alpha channel data completely. The end result is a halving in frame buffer size, cutting the amount of memory demanded by the HDR lighting engine by fifty per cent.

 

[Davros]

amd also have an "enable surface format optimization" check box (looks like they took it out of cat a.i and gave it its own control)
it replaces fp16 with fp11

 

[homerdog]

That's exactly what I linked to. But I dunno if the optimization works on OGL. Worth a shot though, assuming he's on AMD hardware.

 

[FoxMcCloud]

The behavior exhibits itself on my Intel HD 3000 and Radeon HD 6490M GPUs. I'm running on Mac OS X 10.7.2, so that catalyst switch is out. Any ideas?

 

[Davros]

hang on, your copying a texture to one thats 1/4 of the size, getting rid of the alpha channel would be the only way (well not the only way) it would fit
copy the texture to a texture of identical size
ps: any help

No Alpha in the Framebuffer

Be sure you create a double buffered context and make sure you ask for a alpha component.

 

[FoxMcCloud]

I'm sure, I don't think I understand what you said. I'm copying between two RGBA16F textures. I'm using FBO objects that I bind the textures to so I can use BlitFramebuffer() to do the copy with linear filtering for the downsampling. Is there a better way to do that? My windowing system framebuffer is RGBA - unsigned byte. Should that make any difference though?

 

[Dark Helmet]

I have a simple texture blit function in OpenGL that I'm trying to use to copy an RGBA16F texture to another one of 1/4 size ... However, when I use that to copy between two RGBA16F textures Alpha seems to be discarded

Before the blit, add:

glColorMask( GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE );

It is not crystal clear from the spec whether the buffer writemasks are applied in the blit operation (thread link, another link), but I have experienced them to be (with one vendor's drivers at least).

 

[FoxMcCloud]

Nah, same thing. I don't think I ever mask the alpha channel in my app either.