US Patent 7330192 Rendering translucent layers in a display system

A system and method of rendering overlapping layers in a computer display, such as a windowing system, employs front-to-back assembly of the displayed image. An arbitrary number of overlapping elements, such as windows, can be presented, without requiring temporary storage space or additional off-screen buffers. The front-to-back assembly technique minimizes the number of memory transfers performed in connection with rendering an image, and avoids unnecessary reading and processing of pixels that will not contribute to the final image. Special effects such as semi-transparency, shadows, and irregular shapes can be accommodated and processed in an efficient manner.