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Guest Anonymous Poster
Hi There,

Here''s a routine I''ve written for my OpenGL - there''s lots of comments so you should be ok. How you actually save the RGB data is up to you (grab the open-JPEG lib)

// GLubyte * OpenGLScreenGrab()
// User must release the returned buffer ! Will be NULL if failed.
// Note : glPixelTransfer() and glPixelMap() control the output format of the data,
// but by default, provide us with what we need. Also includes glPixelStore() but
// that is called elsewhere for texture creation.
GLubyte * OpenGLScreenGrab()
bool grabbed = false;

// Clear out errors as this is going to be a critical routine for the screen saver
// 2D grabs ...

// Allocate space ...
int bytesPerRow = windowWidth * 3;

GLubyte * buffer1 = new GLubyte[bytesPerRow * windowHeight],
* buffer2 = new GLubyte[bytesPerRow * windowHeight];

// Check all mem grabs and function pointers are available for use ...
if (buffer1 && buffer2 && glReadPixels)
// Reads from the back buffer only. Note that this command *I think* is not available in
// OpenGL V1.0. The default in V1.0 is "to read pixel data from the framebuffer rectangle"
// which I assume to be enough for our purposes.
if (glReadBuffer)

if (!OpenGLErrorDump(true))
// Fetch the pixels ...

if (!OpenGLErrorDump(true))
grabbed = true;

// And do a flip for conveniance ...
for (int r = 0 ; r < windowHeight ; r++)
memcpy(buffer2 + bytesPerRow * r,buffer1 + ((windowHeight - r) - 1) * bytesPerRow,bytesPerRow);

// Did we grab it ?
if (!grabbed)
buffer2 = NULL;

// Free buffer1 and return buffer2 which is left to the calling routine to delete ...

return buffer2;

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