"Clear" stencil buffer manually; workaround for #5490 #5704
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Mimic clearStencil without actually using it by drawing a viewport-sized depth "mask" with value=0
lbud
changed the title
jfirebaugh
approved these changes
Nov 17, 2017
This was referenced Nov 17, 2017
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Does this impact performance ? |
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@SBRK in theory it might impact performance ever so slightly (effectively trading the cost of natively clearing the stencil buffer with the cost of rendering one additional layer; this happens once per source change in the layer order) but it is a necessary workaround to a critical upstream bug. |
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@lbud yep I know we had this problem and it was affecting half the computers in our company :) But it seemed to me the performance was slightly worse after updating. It could just be an impression though |
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As of Chrome v62, depth reads in certain Intel Iris graphics cards (at least Intel Iris Graphics 6100) all fail on intermittent frames, creating a flashing effect as in #5490. I believe this bug is some kind of race condition or incorrect vector access related to stencil buffer clearing. This PR mitigates this issue pending an upstream fix by never using
gl.clear(gl.STENCIL_BUFFER_BIT)and instead "clearing" it manually by drawing a stencil mask of all 0s to the full viewport. I've confirmed on maps where this effect is most dramatic (maps with many sources) that this fix eliminates flashing entirely.Fixes #5490.
Upstream issue: https://bugs.chromium.org/p/chromium/issues/detail?id=784030