Multiple tile output using interface compression in a raster stage

In a GPU (graphics processor unit) a method for interface compression in a raster stage, comprising:

• receiving a graphics primitive for rasterization in a raster stage of a graphics processor;
• rasterizing the graphics primitive at a first level in a coarse raster component to generate a plurality of tiles related to the graphics primitive;
• determining whether a polygon stipple operation is required for the plurality of tiles;
• if a polygon stipple operation is required, outputting a respective plurality of uncompressed coverage masks for the plurality of tiles from the coarse raster component to a fine raster component on a one coverage mask per clock cycle basis, wherein a transfer interface is coupled between the coarse raster component and the fine raster component and is for transferring coverage masks from the coarse raster component to the fine raster component, the transfer interface having a size configured to accept one compressed coverage mask per clock cycle;
• if a polygon stipple operation is not required, outputting a compressed coverage mask for the plurality of tiles in a single clock cycle;
• and
• rasterizing the plurality of tiles at a second-level in the fine raster component to generate a plurality of pixels related to the graphics primitive.

A computer system, comprising:

• a system memory;
• a central processor unit coupled to the system memory;
• and
• a graphics processor unit communicatively coupled to the central processor unit;
• a set-up unit within the graphics processor unit for generating polygon descriptions;
• a rasterizer unit within the graphics processor unit and coupled to the set-up unit for rasterizing the polygon descriptions;
• a coarse raster component within the rasterizer unit for rasterizing the polygon descriptions at a first level to generate a plurality of tiles related to the graphics primitive;
• and
• a fine raster component within the rasterizer unit for rasterizing the plurality of tiles at a second-level to generate a plurality of pixels related to the graphics primitive, wherein upon determining whether a window ID operation or a polygon stipple operation is required for the plurality of tiles:
• the coarse raster component outputs a respective plurality of uncompressed coverage masks for the plurality of tiles to the fine raster component on a one coverage mask per clock cycle basis if a window ID operation or polygon stipple operation is required, wherein a transfer interface is coupled between the coarse raster component and the fine raster component and is for transferring coverage masks from the coarse raster component to the fine raster component, the transfer interface having a size configured to accept one compressed coverage mask per clock cycle;
• and
• the coarse raster component outputs a compressed coverage mask for the plurality of tiles in a single clock cycle to the fine raster component if a window ID operation or polygon stipple operation is not required.