Graphics processing systems

摘要

In a tile-based graphics processing system, when an overlay image is to be rendered onto an existing image, the existing tile data for the existing image from the frame buffer in the main memory is pre-loaded into the local color buffer of the graphics processor (step 41). The overlay content is then rendered and used to modify the tile data stored in the color buffer (step 44). When the data for a given sampling position stored in the tile buffer is modified as a result of the overlay image, a corresponding dirty bit for the tile region that the sampling position falls within is set (step 45). Then, when all the rendering for the tile has been completed, the dirty bits are examined to determine which regions of the tile have been modified (step 46). The modified tile regions are written back to the output image in the frame buffer in the main memory (step 47), but any regions whose dirty bits have not been set are not written back to the frame buffer in the main memory.

主权项

1. A method of operating a graphics processing system when an overlay image is to be overlaid on an existing image for which data is already stored in an output array of data in an output buffer, the method comprising:
reading data for the existing image from the output array of data in the output buffer; using data for the overlay image to modify data for the existing image to generate an overlaid image showing the overlay image overlaid on the existing image; and writing data for the overlaid image back to the output array of data in the output buffer, wherein: the step of writing data for the overlaid image back to the output array of data in the output buffer comprises: determining whether there are any regions of the existing image that have not been modified when modifying the data for the existing image to generate the overlaid image; and for any regions of the existing image that have been determined to have not been modified when modifying the data for the existing image to generate the overlaid image, not writing data for the overlaid image for those unmodified regions of the existing image back to the output array of data in the output buffer, and using the data for those regions of the existing image that is already stored in the output data array in the output buffer for the overlaid image; and the method further comprises: as the overlaid image is rendered, loading any existing image data in the output data array that is needed for the overlay rendering process back into a local memory of the graphics processing system from the output buffer for modification using data for the overlay image to show the overlay image overlaid on the existing image; wherein: the step of loading existing image data in the output data array that is needed for the overlay rendering process back into a local memory of the graphics processing system from the output buffer for modification using data for the overlay image to show the overlay image overlaid on the existing image comprises: identifying regions of the existing image that will be modified using data for the overlay image as the overlaid image is rendered; and when a region of the image has been identified as a region of the existing image that will be modified using data for the overlay image as the overlaid image is rendered, determining whether the existing image data is needed for the modification process, and then only loading the existing image data in that event.