Hidden culling in tile-based computer generated images

• US 10,366,530 B2
• Filed: 10/25/2017
• Issued: 07/30/2019
• Est. Priority Date: 12/20/2012
• Status: Active Grant

• Current Assignee: Imagination Technologies Limited (Imagination Technologies Group Ltd.)
• Original Assignee: Imagination Technologies Limited (Imagination Technologies Group Ltd.)
• Inventors: Yang, Xile, Howson, John W., Fenney, Simon
• Primary Examiner(s): Yang, Andrew G
• Application Number:
  US15/793,343
• Publication Number:
  US 20180108174A1
• Time in Patent Office: 643 Days
• Field of Search: None
• CPC Class Codes: G06T 15/005 General purpose rendering architectures
• CPC Class Codes: G06T 15/405 using Z-buffer

Abstract

A method and system is provided for culling hidden objects in a tile-based graphics system before they are indicated in a display list for a tile. A rendering space is divided into a plurality of regions which may for example be a plurality of tiles or a plurality of areas into which one or more tiles are divided. Depth thresholds for the regions, which are used to identify hidden objects for culling, are updated when an object entirely covers a region and in dependence on a comparison between a depth value for the object and the depth threshold for the region. For example, if the depth threshold is a maximum depth threshold, the depth threshold may be updated if an object entirely covers the tile and the maximum depth value of the object is less than the maximum depth threshold.

Claims

1. A tile-based graphics system comprising:

a processor configured to implement (i) a tiling process to derive a display list for each of a plurality of tiles, and (ii) a rendering process to render the tiles using the respective derived display lists;

wherein the tiling process comprises, for each of a plurality of regions of a tile;

determining one or more depth values for an object located within the region;

comparing the one or more determined depth values for the object with a depth value associated with the region;

determining whether to include an indication of the object in the display list for the tile in dependence on the result of at least one of the one or more comparisons for each of the plurality of regions of the tile; and

if the object entirely covers the region, updating said depth value associated with the region in dependence on the result of at least one of the one or more comparisons;

wherein the tiling process further comprises outputting the display list for the tile for storage in a memory; and

wherein the rendering process comprises retrieving the display list for the tile from the memory and rendering the tile using the retrieved display list for the tile.

2. The system according to claim 1, wherein the object comprises a single primitive, a plurality of primitives or a patch of surface data.

3. The system according to claim 1, wherein the comparisons between the depth values for the object and the depth value associated with the region comprise a comparison between a maximum depth value for the object and a maximum depth value associated with the region;

and

wherein the step of updating the depth value associated with the region in dependence on the result of at least one of the one or more comparisons comprises updating the maximum depth value associated with the region if the maximum depth value for the object is less than the maximum depth value associated with the region.

4. The system according to claim 3, wherein determining whether to include an indication of the object in the display list for the tile in dependence on the result of at least one of the comparisons for each of the one or more regions of the tile with the depth value associated with the region, comprises comparing a minimum depth value for the object to the maximum depth value associated with the region.

5. The system according to claim 3, wherein the processor is further configured to perform a comparison between a minimum depth value for the object and a minimum depth value associated with the region;

and update the minimum depth value associated with the region if the minimum depth value for the object is less than the minimum depth value associated with the region to a value equal to or less than the minimum depth value for the object.

6. The system according to claim 1, wherein performing comparisons between the depth values for the object and the depth value associated with the region comprises performing a comparison between a minimum depth value for the object and a minimum depth value associated with the region;

and

wherein updating the depth value associated with the region in dependence on the result of at least one of the one or more comparisons comprises updating the minimum depth value associated with the region if the minimum depth value for the object is greater than the minimum depth value associated with the region.

7. The system according to claim 6, wherein determining whether to include an indication of the object in the display list for the tile in dependence on the result of at least one of the comparisons for each of the one or more regions of the tile with the depth value associated with the region, comprises comparing a maximum depth value for the object to the minimum depth value associated with the region.

8. The system according to claim 6, wherein the processor is further configured to perform a comparison between a maximum depth value for the object and a maximum depth value associated with the region;

and updating the maximum depth value associated with the region if the maximum depth value for the object is greater than the maximum depth value associated with the region to a value equal to or greater than the maximum depth value for the object.

9. The system according to claim 1, wherein deriving a depth value for the object comprises, for each region within which the object is located, deriving a depth value for the respective part of the object within that region.

10. The system according to claim 1, wherein determining whether to include an indication of the object in the display list for the tile in dependence on the result of at least one of the one or more comparisons for each of the regions of the tile comprises, for each of the regions of the tile within which the object is located, comparing a depth value for the object to the depth value associated with that region.

11. The system according to claim 1, wherein the processor is further configured to determine a depth value associated with the tile based on the depth value associated with each of the regions of the tile;

and write the depth value associated with the tile to a memory.

12. The system according to claim 11, wherein determining a depth value associated with the tile based on the depth value associated with each of the regions of the tile comprises determining the greatest of the depth values associated with the regions of the tile;

and setting the depth value associated with the tile to a value equal to or greater than the greatest of the depth values associated with the regions of the tile.

13. The system according to claim 11, wherein determining a depth value associated with the tile based on the depth value associated with each of the regions of the tile comprises determining the smallest of the depth values associated with the regions of the tile and setting the depth value associated with the tile to a value equal to or smaller than the smallest of the depth value associated with the regions of the tile.

14. The system according to claim 11, wherein the depth values associated with the regions are written to a memory for temporarily storing data.

15. The system according to claim 14, wherein the processor is configured to determine depth values associated with the regions to be evicted from the memory based on at least one of (1) a count of how many of the depth values associated with the regions have been updated and (2) on the difference between the depth values associated with the regions.

16. The system according to claim 1, wherein a first plurality of the plurality of regions is a plurality of sub regions into which a first portion of the tile is subdivided, and wherein the processor is further configured to determine a depth value associated with the first portion of the tile based on the depth value associated with each of the sub regions;

and write the depth value associated with the first portion of the tile to a memory.

17. A method of rendering in a tile-based graphics system, the method comprising:

implementing a tiling process to derive a display list for each of a plurality of tiles, wherein the tiling process comprises;

for each of a plurality of regions of a tile;

determining one or more depth values for an object located within the region;

comparing the one or more determined depth values for the object with a depth value associated with the region;

determining whether to include an indication of the object in the display list for the tile in dependence on the result of at least one of the one or more comparisons for each of the plurality of regions of the tile; and

if the object entirely covers the region, updating said depth value associated with the region in dependence on the result of at least one of the one or more comparisons; and

outputting the display list for the tile for storage in a memory; and

implementing a rendering process to render the tiles using the respective derived display lists, wherein the rendering process comprises retrieving the display list for a tile from the memory and rendering the tile using the retrieved display list for the tile.

18. A circuit for a tile-based graphics system, the circuit being configured to implement (i) a tiling process to derive a display list for each of a plurality of tiles, and (ii) a rendering process to render the tiles using the respective derived display lists;

wherein the tiling process comprises, for each of a plurality of regions of a tile;

determining one or more depth values for an object located within the region;

comparing the one or more determined depth values for the object with a depth value associated with the region;

determining whether to include an indication of the object in the display list for the tile in dependence on the result of at least one of the one or more comparisons for each of the plurality of regions of the tile; and

if the object entirely covers the region, updating said depth value associated with the region in dependence on the result of at least one of the one or more comparisons;

wherein the tiling process further comprises outputting the display list for the tile for storage in a memory; and

wherein the rendering process comprises retrieving the display list for the tile from the memory and rendering the tile using the retrieved display list for the tile.