[Mesa-dev] [Bug 78914] [llvmpipe] Front/Backfaces do not get the same depth values when interpolated

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=78914

--- Comment #24 from José Fonseca <jfonseca at vmware.com> ---
(In reply to Kurzemnieks from comment #23)
> I think I have run in the same problem. 
> Here is a screenshot with a simple double-sided cube whose backface seems to
> be drawn incorrectly on the edge.
> https://api1-ams2.monosnap.com/static/0kwtTWiNWJrcIXex8BcxpgoWCkxHGx.png

Link is dead.

Maybe try using Buzilla's attachment feature -- might be good for future
reference too.

> So what is the best workaround for this if it won't be fixed?

The "workaround" (although I'd merely call it "best practice") is to make
adequate use of glPolygonOffset.

See for example http://www.zeuscmd.com/tutorials/opengl/15-PolygonOffset.php


In short the whole idea consists in: instead of assuming that two draw calls
will produce _exactly_ the same depth values, give a tolerance so to accomodate
small differences. glPolygonOffset allows to do that.

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