5.2 GLR Support via OpenGL Extensions

OpenGL is extensible so it is appropriate to consider what extensions to OpenGL would improve the perceived and actual performance of GLR. Possibilities include:

• Compressed image formats to compress pixels read from and uncompress pixels displayed to the frame buffer.

• An extension to add a scan-line skip count (0 by default) indicating how many scan-lines to skip between every scan-line drawn to or read from the frame buffer. A scan-line skip count of 1 would permit even and odd scan-line interleaving. A GLR client could read back all the odd scan-lines (or every third scan line, etc.) and immediately display them; afterword, read and display the even scan-lines. This incremental display might give the GLR application user faster perceived feedback.

• Using OpenGL's existing copy texture extension, perform staged read backs by reading back the frame buffer state into a texture object, end the render interval, call glrEstablishRenderState, and then (outside the render interval) read the texture object's contents (possible because texture objects are render state, not frame buffer state) back to the GLR client. This allows another render interval to be scheduled while the previous client is still reading back its frame buffer state.

• The described GLR implementation based on glrmanager dedicates the high-end graphics subsystem to GLR. This is a serious disadvantage because a machine set up to work as a GLR render server will not be available for normal window system sessions. If GLR render intervals can be implemented using OpenGL pixel buffers instead of windows so that render intervals would use off-screen memory for their rendering, the graphics subsystem might be able to support both GLR and a window system simultaneously.