occlusion query

[Juraj Bleho]

Hi,

I implemented Order independent transparency using depth peeling. I use gl.beginQuery(gl.ANY_SAMPLES_PASSED, query) to detect how many layers are used. It works on windows but not on iOS. On iOS I gets almost always false positive result (rarely false negative)).

I am using two depth test. One native and One in shader with discard. Native one seems to work.

It looks like query works only with early Z test. When I do discard or modify gl_FragDepth, which disable early depth test, it doesn't work properly.

Any ideas?

[Ken Russell]

Hi Juraj,

Please file a bug on bugs.webkit.org under component "WebGL" and include the smallest possible test case you can come up with which shows the failures. Please feel free to post the bug ID here once filed.

There have been some bugs in this area in the WebGL/Metal backend, which Safari uses, and which Chrome is moving to. Both Apple and Google are actively working on fixing these, so any additional test cases observed to fail would be helpful.

Thanks,

-Ken

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[Shrek Shao]

FYI you might find the new extension OES_draw_buffers_indexed useful for depth peeling, which gives you ability to have separate blending ops for each color output.

[Juraj Bleho]

Bug id on webkit is 238328