Threads in Picture (nVidia)

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Threads in Picture (nVidia)

Postby Snover » 2003-7-13 @ 00:27

When "Enable conformant texture clamp behaviour" is enabled for OpenGL in the nVidia display control panel, threads appear in the picture, dividing it into two horizontal strips and three vertical strips. (1024x768, I assume that this increases/decreases according to the resolution). Something to look at.
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Postby HunterZ » 2003-7-13 @ 01:45

Which picture? Windows? Or OpenGL apps? That is interesting...I can't verify it with my GF2MX because it's packed away for several more days until I finish moving. The option is disabled by default IIRC, so it's probably nothing to worry about. My guess is that the option is there in case some app does something differently and looks wrong without the option on.
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Postby Glidos » 2003-7-13 @ 08:33

That used to happen all that time because of a bug in Glidos, but I fixed that and I don't know why that setting should break it.

When the process of texturing runs off the end of a texture there's two ways out: either go back to the beggining of the texture and repeat the whole thing again, or take the last pixel color and clamp to that for then on. These "threads" appear when the former method is used in place of the latter.
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Postby HunterZ » 2003-7-13 @ 18:01

Oh I see...The threads appear because of rounding error - the texture is probably supposed to end right at the edges of the polygons, but due to finite precision, it probably doesn't always turn out that way.
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Postby Snover » 2003-7-13 @ 22:13

It hasn't occurred in any other OpenGL software I've used to date.
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Postby Glidos » 2003-7-13 @ 22:53

HunterZ wrote:Oh I see...The threads appear because of rounding error - the texture is probably supposed to end right at the edges of the polygons, but due to finite precision, it probably doesn't always turn out that way.


Yes, but the game should set clamping mode rather than wrapping mode so that it doesn't matter. I know TR and Redguard get this right because I used to have a bug that caused Glidos to ignore the clamping mode. This caused threads, which disappeared when I fixed the bug.

Even when the bug was present, the threads didn't appear when Glidos was set to the game's native resolution, because there wasn't a pixel in a position that could show up the rounding error.
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