Architecutre for a window-based graphics system

Abstract

A computer graphics system comprises a main CPU, a main system memory and a graphics subsystem for displaying graphical images on a display terminal. A system bus enables the main CPU, main system memory and graphics subsystem to transmit data among one another. The graphics subsystem comprises a graphics controller in communication with the system bus, a frame buffer for storing pixels displayed on the display terminal, and a separate off-screen memory unit located within the graphics subsystem for storing off-screen pixels in a linear format. A local bus is included in the graphics subsystem for transmitting data within the graphics subsystem among the frame buffer, the off-screen memory and the graphics controller. The graphics controller includes an address processing unit for converting between two-dimensional addresses and linear format addresses utilized by the off-screen memory unit. In the inventive computer graphics system address conversions required for executing graphical operations and block swaps between the off-screen memory and the frame buffer are performed in the graphics controller rather than in the main CPU. Thus, the inventive graphics system makes more efficient use of CPU resources than a conventional architecture.