glFeedbackBuffer

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glFeedbackBuffer Interface to OpenGL function glFeedbackBuffer

usage: glFeedbackBuffer( bufsize, buftype, bufferptr )

bufsize is the number of float values that can be written into the buffer.
Caution: A float takes up 4 bytes, so the size of the allocated buffer needs
to be at least 4*bufsize!

buftype is a GLenum specifiying the type of requested information. See OpenGL manual.

bufferptr is a pointer to a buffer allocated via bufferptr=moglmalloc() or bufferptr=moglcalloc().

Example of usage:

1. Allocate a buffer of proper size to hold the information you want OpenGL to return:
bufferptr = moglmalloc(bufsize * 4);

2. Set this memory buffer as feedback buffer and tell GL which kind of info about each
primitive should be fed back. E.g., GL.2D would return projected 2D screen coordinates of
each transformed vertex.
glFeedbackBuffer(bufsize, GL.2D, bufferptr);

3. Switch OpenGL from normal rasterization (=drawing) mode into feedback mode. Executing
drawing commands will not create any visible drawing, but will only store the results
of geometric transform, culling and lighting operations into your buffer 'bufferptr':
glRenderMode(GL.FEEDBACK);

4. Draw your scene...

5. Switch back to normal rendering. This will return the number of actually fed back items:
itemcount = glRenderMode(GL.RENDER);

6. Return the content of the memory feedback buffer as a new Matlab matrix:
myfeedbackresult = moglgetbuffer(bufferptr, GL.FLOAT, itemcount*4);

7. Interpret and use content of myfeedbackresult as described in the manual for glFeedbackBuffer.