Occlusion queries in graphics processing

A method of performing occlusion queries in a graphics processing system in which a counter for an occlusion query is maintained in a cache memory associated with the graphics processing system and written back to main memory for the graphics processing system for further processing, the method comprising:

• when a new counter in the cache memory is to be allocated to an occlusion query, sending a memory request to the main memory to load a previous counter value for that occlusion query that is stored in the main memory;
• using the occlusion counter in the cache memory to maintain a temporary count of the results of the occlusion query whilst waiting for the memory request to the main memory to complete;
• and
• when the previous counter value for the occlusion query from the main memory is returned in response to the memory request, combining that loaded previous counter value with the temporary value being maintained by the occlusion counter in the cache memory;
• and
• thereafter continuing to process the occlusion query using the occlusion counter in the cache memory.

A graphics processing system comprising:

• at least one graphics processing core;
• a local memory associated with the at least one graphics processing core;
• and
• a main memory of or associated with the graphics processing system;
• and wherein
• the graphics processing system is configured to, when an occlusion query is to be performed:
• allocate an occlusion counter for the occlusion query in the main memory of or associated with the graphics processing system;
• provide in the local memory associated with the at least one graphics processing core, a local occlusion counter to be used for the respective occlusion query;
• use the local occlusion counter in the local memory to count results of the occlusion query;
• and
• once the local occlusion counter in the local memory has counted results of the occlusion query, write the counter value for the local occlusion counter from the local memory to the allocated occlusion counter for the occlusion query in the main memory of or associated with the graphics processing system.

A graphics processing system in which a counter for an occlusion query is maintained in a cache memory associated with the graphics processing system and written back to main memory for the graphics processing system for further processing, the graphics processing system further being configured to:

• when a new counter in the cache memory is to be allocated to an occlusion query, send a memory request to the main memory to load a previous counter value for that occlusion query that is stored in the main memory;
• use the occlusion counter in the cache memory to maintain a temporary counter of the results of the occlusion query whilst it is waiting for the memory request to the main memory to complete;
• and
• when the previous counter value for the occlusion query from the main memory is returned in response to the memory request, combine that loaded previous counter value with the temporary value being maintained by the occlusion counter in the cache memory;
• and
• thereafter continue to process the occlusion query using the occlusion counter in the cache memory.

One or more non-transitory computer readable storage devices having computer readable code embodied on the computer readable storage device for programming one or more data processors to perform a method of performing occlusion queries in a graphics processing system, the method comprising:

• when an occlusion query is to be performed:
• allocating an occlusion counter for the occlusion query in a main memory of or associated with the graphics processing system;
• providing in a local memory of or associated with the graphics processing system, a local occlusion counter to be used for the respective occlusion query;
• and
• using the local occlusion counter in the local memory to count results of the occlusion query;
• and
• once the local occlusion counter in the local memory has counted results of the occlusion query, writing the counter value for the local occlusion counter from the local memory to the allocated occlusion counter for the occlusion query in a main memory of or associated with the graphics processing system.