Fix flickering for tileset with thin walls #5940
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This looks good to me, but you have to update the failing back face test. |
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Just pushed the commit right as you commented. |
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Bump - so this gets into the release. |
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This builds on #5820 which is the right idea but for me didn't completely solve the flickering, especially on the roof of the AGI building.
Originally I thought the flickering was caused by children rendering with their parents, but the problem is actually rendering the back faces and front faces of the same tile simultaneously, as required by the skip-lods approach. Normally this is never a problem, but it is a huge problem for thin walls where back and front faces overlap. Fixing the depth test in #5820 to allow the front face to render above the back face when it's depth is equal seems like it should work, but I think the test is too precise. Apply a polygon offset to the back faces seems to work better. Essentially it pushes the back face depth to "solidify" the geometry.
At some point @austinEng and I talked about disabling color-writes for the back face commands, and I think that was kept in because of this flickering bug, the rationale being it's better to show the back face color during the flicker rather than see through the model. Because the flickering is mostly gone now I disable color writes for back faces, hopefully we get some performance win there.
The last thing in this PR is not rendering back faces for leaf tiles. I think there could be an edge case here where a tile further in the distance with a greater selection depth could appear in front of the tile up close, but I think this situation is rare and haven't noticed it happen yet during my testing.
Before and after: