glReadPixels ??
Author
Hi
Here is my simple code :
unsigned char* buffer = new unsigned char[width * height * 3];
glReadPixels(0, 0, width, height, GL_BGR_EXT, GL_UNSIGNED_BYTE, buffer);
but I get an error from glReadPixels : GL_INVALID_OPERATION
this code is not between glBegin / glEnd
Does anyone has an example of glReadPixels ?
I just want to get the frame buffer and to save it in a file
Is it the best solution to do that ? and how to use glReadPixels ??
thx a lot ... ^^
Here's what the blue book says about errors glReadPixels can cause
The only thing I can see with your code that may be what's causing the error is the use of GL_BGR_EXT (though I would've thought you'd be able to use it here), however that should cause a GL_INVALID_ENUM error, not a GL_INVALID_OPERATION error. Try using GL_RGB or something like that, it may work.
[edit]Well the extension description in the extension registry clearly states you can use GL_BGR_EXT for glReadPixels which isn't surprising as it's an extension for use with glReadPixels (which I didn't know before) [smile] , so it's most likely an invalid context like chowe6685 said[/edit]
Quote:GL_INVALID_ENUM is generated if format or type is not an accepted value.
GL_INVALID_VALUE is generated if either width or height is not negative.
GL_INVALID_OPERATION is generated if format is GL_COLOR_INDEX and the color buffers store RGBA color components.
GL_INVALID_OPERATION is generated if format is GL_STENCIL_INDEX and there is no stencil buffer.
GL_INVALID_OPERATION is generated if format is GL_DEPTH_COMPONENT and there is no depth buffer.
GL_INVALID_OPERATION is generated if glReadPixels is called between a call to glBegin and the corresponding call to glEnd.
The only thing I can see with your code that may be what's causing the error is the use of GL_BGR_EXT (though I would've thought you'd be able to use it here), however that should cause a GL_INVALID_ENUM error, not a GL_INVALID_OPERATION error. Try using GL_RGB or something like that, it may work.
[edit]Well the extension description in the extension registry clearly states you can use GL_BGR_EXT for glReadPixels which isn't surprising as it's an extension for use with glReadPixels (which I didn't know before) [smile] , so it's most likely an invalid context like chowe6685 said[/edit]
Author
well...
Yes, I think my context is correct, I can draw geometry, I have camera, lights, maps ..etc..
I surely did a mistake in the initialisation
Can you give me the steps to init this context ? just to check if mine is correct ??
thx ...
Yes, I think my context is correct, I can draw geometry, I have camera, lights, maps ..etc..
I surely did a mistake in the initialisation
Can you give me the steps to init this context ? just to check if mine is correct ??
thx ...
try the GL_RGB thingo, also check that your not trying
to copy a rect. thats larger than your screen size. test
it out with copying 256x256 first
if that fails, you could always try using glCopyTexSubImage2D
tried checking the specs on this extension?
http://oss.sgi.com/projects/ogl-sample/registry/EXT/bgra.txt
to copy a rect. thats larger than your screen size. test
it out with copying 256x256 first
if that fails, you could always try using glCopyTexSubImage2D
tried checking the specs on this extension?
http://oss.sgi.com/projects/ogl-sample/registry/EXT/bgra.txt
Author
well thx but I dont think this function is usefull for me
I tried GL_RGB and I've got the same result :(
About the OGL context, I've read somewhere that we must use functions like glReadBuffer or glPixelStore before glReadPixels... ??
DO you have any ideas on it ?
I just want to get the frame buffer and save it in a file
thx
I tried GL_RGB and I've got the same result :(
About the OGL context, I've read somewhere that we must use functions like glReadBuffer or glPixelStore before glReadPixels... ??
DO you have any ideas on it ?
I just want to get the frame buffer and save it in a file
thx
thats a really strange problem, i've never ever setup a context
in any kind of special manner, and have used glReadPixels without
problems.
could you provide any code? that would help...
in any kind of special manner, and have used glReadPixels without
problems.
could you provide any code? that would help...
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