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View Full Version : Centroid AA on GeForce 8?


Monkish
05-26-08, 12:39 PM
I've started to play Half-Life 2 again, but on my more recent GeForce 8800 GTX card rather than my original Radeon 1900 XTX card. Unfortunately I'm getting those annoying white lines at distance due to the out-of-bounds AA sampling problem. Back in 2006 there was talk of this being fixed by either centroid AA or a pixel shader workaround in future drivers or hardware. Was this ever implemented? Is there any way to get these white lines removed, or is it just an oversight in the texture/mesh alignment of the original HL2 levels?

HiCZoK4
05-26-08, 12:50 PM
I also have those lines at textures :\

XDanger
05-26-08, 01:52 PM
Which lines?

HiCZoK4
05-26-08, 02:05 PM
Especially on hl2. Lines which CUT textures from each other at distance. Those blend as you walk to them.
Not seen on every textures thou

Monkish
05-28-08, 08:14 AM
Here's an example image segment that flips between No AA and 4X TAA. Notice how the transparency AA improves the look of the tree and telegraph wires, but also how it introduces all those hideous vertical and horizontal white line glitches. This was taken from Valve & NVIDIA software and hardware circa May 2008. So much for having addressed the problem since 2004.

http://accelenation.com/files/hl_aa_bug.gif

walterman
05-28-08, 11:19 AM
Use gamma correction AA to avoid those issues. It enhances the distribution of the colors that are used to smooth the transitions at the edges of the polys. It has no performance hit.

Armed_Baboon
05-28-08, 05:31 PM
Here's an example image segment that flips between No AA and 4X TAA. Notice how the transparency AA improves the look of the tree and telegraph wires, but also how it introduces all those hideous vertical and horizontal white line glitches. This was taken from Valve & NVIDIA software and hardware circa May 2008. So much for having addressed the problem since 2004.

http://accelenation.com/files/hl_aa_bug.gif

source engine is starting to look very old...

Monkish
05-29-08, 07:38 AM
Actually, turning gamma correction off reduces the brightness of the glitches slightly and leads to a marginal improvement. Here's a higher resolution comparison...

http://accelenation.com/files/hl_aa_bug2.gif

Monkish
05-30-08, 05:18 AM
I suspect that this problem was caused by a sloppy level editor that permitted small misalignment errors to go unnoticed in the underlying level mesh. Effectively, any game level should be a single coherent mesh with no discontinuities. MSAA simply revealed these errors, but by that time it was too late. Going back over all the levels to detect and then correct these tiny errors was simply not worth the trouble. Valve have probably since improved their level editor and design process to insure such errors do not exist.

http://accelenation.com/files/example1.gif

Here’s a simple example. The square in the left image has vertex B, but the rectangle has no corresponding vertex B (along edge AC). Any small error in the position of vertex B will produce a misalignment in the abutting edges AC (side of rectangle) and BC (side of square). This will lead to slightly different alias stepping along each edge. This error is not so obvious when it causes the two shapes to overlap slightly, but can show up as AA sub-sample errors especially in the distance as the Z-buffer loses spatial accuracy. A good level editor will further subdivide the rectangle so that it does share the same vertex (E), as shown in the example on the right. In this case the mesh is consistent and has no discontinuities.