Transformed geometry data cache for graphics processing systems

Abstract

A tag buffer implements a tag buffer stage of a rasterization phase in a tile-based rendering graphics processing system having a rendering space sub-divided into a plurality of tiles to which primitives can be associated. A buffer stores an identifier that identifies a visible primitive fragment at each sample position of a tile of the plurality of tiles. A look-up table stores an entry for transformed primitive blocks that indicates whether the tag buffer has received information identifying a primitive fragment associated with that transformed primitive block. The tag buffer receives information identifying primitive fragments that have survived a depth test, updates the buffer to indicate that an identified primitive fragment is the visible primitive fragment at the associated sample position, updates the look-up table to indicate which transformed primitive blocks the identified primitive fragments are associated with, and in response to flushing the contents of the buffer, compares the flushed contents of the buffer to the look-up table to thereby identify transformed primitive blocks that did not survive the tag buffer stage.