Graphics Reference
In-Depth Information
Example 12-1
Copying Pixels Using Framebuffer Blits
(continued)
// Copy the output red buffer to lower-left quadrant
glReadBuffer ( GL_COLOR_ATTACHMENT0 );
glBlitFramebuffer ( 0, 0,
esContext->width, esContext->height,
0, 0,
esContext->width/2, esContext->height/2,
GL_COLOR_BUFFER_BIT, GL_LINEAR );
// Copy the output green buffer to lower-right quadrant
glReadBuffer ( GL_COLOR_ATTACHMENT1 );
glBlitFramebuffer ( 0, 0,
esContext->width, esContext->height,
esContext->width/2, 0,
esContext->width, esContext->height/2,
GL_COLOR_BUFFER_BIT, GL_LINEAR );
// Copy the output blue buffer to upper-left quadrant
glReadBuffer ( GL_COLOR_ATTACHMENT2 );
glBlitFramebuffer ( 0, 0,
esContext->width, esContext->height,
0, esContext->height/2,
esContext->width/2, esContext->height,
GL_COLOR_BUFFER_BIT, GL_LINEAR );
// Copy the output gray buffer to upper-right quadrant
glReadBuffer ( GL_COLOR_ATTACHMENT3 );
glBlitFramebuffer ( 0, 0,
esContext->width, esContext->height,
esContext->width/2, esContext->height/2,
esContext->width, esContext->height,
GL_COLOR_BUFFER_BIT, GL_LINEAR );
}
Framebuffer invalidation gives the application a mechanism to inform the
driver that the contents of the framebuffer are no longer needed. This allows
the driver to take several optimization steps: (1) skip unnecessary restoration
of the contents of the tiles in tile-based rendering (TBR) architecture for
further rendering to a framebuffer, (2) skip unnecessary data copying
between GPUs in multi-GPU systems, or (3) skip flushing certain caches in
some implementations to improve performance. This functionality is very
important to achieve peak performance in many applications, especially
those that perform significant amounts of off-screen rendering.
