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Problems with creating a float pbuffer using CGL/AGL

Hi,
I have been trying to get a float pbuffer working on my powerbook (radeon 9600). I can create a pbuffer in either CGL or AGL without any problems, but they seem to be clamped between 0 and 1. They also are not full precision floats, even though the created pixel format is 128 bit and does use float pixels. The values read back are not, however, fractions of 255, which indicates they are some kind of fixed floating point values. The simplest test was to do a glClear with negative color values or values >1.

In linux i get the correct values from a readback if i create the context and the pbuffer using the glx commands for it, but in OSX they are clamped.

Is it possible to get non-clamped values from a pbuffer in OSX?

Here's the code i use to create the buffers with CGL. The agl version is almost identical.

CGLPBufferObj _hPBuffer;
CGLContextObj _hPBContext;
 _hPBscreen;

 activatePBuffer(){
CGLSetCurrentContext(_hPBContext);
CGLSetPBuffer(_hPBContext, _hPBuffer, , , _hPBscreen);
}

 createPBuffer( width, height){
CGLPixelFormatAttribute attribs[];
GLint ind = ;
ATTR_ADD(kCGLPFAAllRenderers);
ATTR_ADD(kCGLPFAColorFloat);
ATTR_ADDV(kCGLPFAColorSize, );
ATTR_ADD(kCGLPFAAccelerated);
ATTR_ADD(kCGLPFANoRecovery);
ATTR_ADD(kCGLPFAPBuffer);
ATTR_ADD(AGL_NONE);

 nScreens=;
CGLPixelFormatObj pix;
CGLChoosePixelFormat( attribs, &pix, &nScreens );
CGLCreateContext( pix, , &_hPBContext);
CGLError err = CGLCreatePBuffer(width, height, GL_TEXTURE_RECTANGLE_ARB, GL_RGBA, , &_hPBuffer);
printf("Failed to create pbuffer? %i\n", err);
CGLGetVirtualScreen(_hPBContext, &_hPBscreen);
}

My glReadBack call is fairly standard:
], params[],GL_RGBA,GL_FLOAT,texture);

I have queried the GL_COLOR_FLOAT_APPLE enum, and it reports true, so i'm really not sure where i am going wrong.
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