[Bug 18993] Shadows and selection circles z-fight in World of Warcraft

[wine-bugs at winehq.org]

http://bugs.winehq.org/show_bug.cgi?id=18993





--- Comment #6 from Dorek Biglari <dbiglari at gmail.com>  2009-12-30 02:11:22 ---
It scales the depth bias value to be in the correct range. I know it works on
my hardware, an NVidia 6xxx running World of Warcraft in with a 24 bit depth
buffer, but I'd like to know if it works on all configurations, or if it helps
other apps. The number I divided by I got from the website:
http://aras-p.info/blog/2008/06/12/depth-bias-and-the-power-of-deceiving-yourself/

The author is discussing a cross platform app he's writing using OpenGL and
Direct3d.  The Direct3d users were complaining about zfighting.  I'll quote the
pertinent parts:

"How do you apply depth bias in OpenGL? Enable GL_POLYGON_OFFSET_FILL and set
glPolygonOffset to something like -1, -1. This works.

How do you apply depth bias in Direct3D 9? Conceptually, you do the same. There
are DEPTHBIAS and SLOPESCALEDEPTHBIAS render states that do just that. And so
we did use them.

And people complained about funky results on Windows."

He then goes on to state that he thought it was because people were using
terrible near/far planes, which is what I would think too.  And I think thats
probably why Lisa's patch also seems to correct the problem, because its
messing with the projection.  But the guy hits on an issue I have run into with
Direct3D before, that is that the documentation on the depth bias is wrong.

Continuing to quote from him:

"First, depth bias documentation on Direct3D is wrong. Depth bias is not in
0..16 range, it is in 0..1 range which corresponds to entire range of depth
buffer."

...

"So yeah, the proper multiplier for depth bias on Direct3D with 24 bit depth
buffer should be not 1.0/65535.0, but something like 1.0/(2^24-1). Except that
this value is really small, so something like 4.8e-7 should be used instead
(see Lengyel’s GDC2007 talk). Oh, but for some reason it’s not really enough in
practice, so something like 2.0*4.8e-7 should be used instead (tested so far on
GeForce 8600, Radeon HD 3850, Radeon 9600, Intel 945, reference rasterizer).
Oh, and the same value should be used even when a 16 bit depth buffer is used;
using 1.0/65535.0 multiplier with 16 bit depth buffer produces way too large
bias."

I've been running Wow and wine with this patch and it fixes the problem and I
have not noticed any side effects.  Out of curiosity, why do you think it looks
incorrect, Henri? If I am wrong here I would like to know. I assume that you
have seen the z-fighting that Lisa reported.  Let me know your thoughts.

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