Swaps a region of the back buffer being rendered too, to the front for display.
rectangles represents the region as array of
n_rectangles each defined by 4 sequential (x, y, width, height)
This function also implicitly discards the contents of the color, depth and stencil buffers as if discard_buffers were used. The significance of the discard is that you should not expect to be able to start a new frame that incrementally builds on the contents of the previous frame.
A Onscreen framebuffer
An array of integer 4-tuples representing rectangles as (x, y, width, height) tuples.
The number of 4-tuples to be read from