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FBO + GL_RGBA_FLOAT32_ATI?

Started by Hnefi Apr 15, 2006 at 5:08 AM 7 replies 3.8k views

Original Post

Apr 15, 2006 at 5:08 AM

Some effects I need to implement seem to require the use of a texture in GL_RGBA_FLOAT32_ATI format. Trouble is, I want to be able to modify this texture using FBO's. When I try to do so, my FPS drops from 100+ to maybe 0.05. Are FBO's incompatible with GL_RGBA_FLOAT32_ATI or is there simply something particular that needs to be done in order for this format not to affect performance?

Code-R

Apr 15, 2006 at 4:34 PM

what gpu/driver?

Sepultang

Apr 15, 2006 at 4:46 PM

GL_RGBA_FLOAT32_ATI works perfectly fine with FBOs, I use it myself. Make sure you create your floating point textures correctly, using format GL_RGBA and type GL_FLOAT and filters as GL_NEAREST.

You should get error messages from the fbo if something is wrong, make sure you check this using glCheckFramebufferStatusEXT.

MARS_999

Apr 15, 2006 at 7:33 PM

I am assuming this works to then...
GL_RGBA32F_ARB

Hnefi

Apr 16, 2006 at 3:22 AM

I'm using a GF 6800 with the latest drivers. I don't think I was using the GL_RGBA format - IIRC I was using GL_RGB. Maybe that's what's wrong. I'll make sure to check up on it tonight. I'll reply here again if it doesn't work.

Thanks.

Expandable

Apr 16, 2006 at 7:21 AM

Make sure you only use the GL_NEAREST filter on 32bit floating point textures, otherwise it will run in software.

SteveXP

Apr 16, 2006 at 11:12 AM

Jep, Expandable is right.

If you really nead GL_LINEAR then you should check if FLOAT16 is sufficient for you.
With FLOAT16, GL_LINEAR and Mipmapping are Supported on Nvidia Cards (GF6 upwards). Currently ATI doesn't support it, but it will do with the next generation.

Hnefi

Apr 16, 2006 at 1:57 PM

This is the code I use, which produces horrible performance:

displacementbuffer = 0;glGenFramebuffersEXT(1, &displacementbuffer);glBindframebufferEXT(GL_FRAMEBUFFER_EXT, displacementbuffer);glGenTextures(1, &displacementmap);glBindTexture(GL_TEXTURE_2D, displacementmap);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);//glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE_FLOAT32_ATI, width, height, 0, GL_LUMINANCE, GL_FLOAT, 0);glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA_FLOAT32_ATI, width, height, 0, GL_RGBA, GL_FLOAT, 0);//glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, width, height, 0, GL_RGB, GL_FLOAT, 0);glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT, GL_TEXTURE_2D, displacementmap, 0);

If I use the code as it is above, the buffer is written to when I enable it and I can see the results if I display the texture on a mesh, but performance is abysmal. If I instead use the commented line with GL_RGBA8, performance is great, but I can't use that because apparently, textures in that format can't be used as textures in the vertex shader (which is what I need the texture for). If I use the commented line with GL_LUMINANCE, nothing is written to the buffer (at least nothing gets displayed), although apparently that texture format can be passed to the vertex shader so if I could get that to work it would be just as good as getting GL_RGBA_FLOAT32_ATI to work.

glCheckFramebufferStatusEXT() claims the framebuffer is ok.

Note: I do use another framebuffer in the program with GL_RGBA8 format, using GL_COLOR_ATTACHMENT0_EXT. Could that be an issue? I tried using another color attachment, but if I do, nothing gets rendered to the buffer.

Sepultang

Apr 17, 2006 at 5:47 AM

You're texture-code looks ok to me. Also, using many FBOs with GL_COLOR_ATTACHMENT0_EXT should not cause any problem.

You could try this program which will create a bunch of floating point texture formats and attach them to FBOs, saving the results to a file. So you will know if there's something wrong with your card/driver.
http://www.mathematik.uni-dortmund.de/~goeddeke/gpgpu/basic_math_tutorial_cg.zip

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