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White dots & strings of dots in many games, what exactly are they??

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This has been bugging the crap out of me for awhile now. I first seen them when I started playing Motocross madness 2. I noticed that where two textures might meet or in a "seam", little white dots and strings often appear then disappear. Since then I have seen them in alot of other games too. At first I thought my Geforce DDR card must be shot, so I replaced it with a prophet 2-64 mb card and that didnt help. I was perplexed. Anyway I proceeded to try everything under the sun to fix this including getting a new free motherboard from Dell and reformatting my HD. Nothing frickin worked. Totally stumped at what was causing this I then did something I should have done sooner. I brought a few of the games into my work and tried them on 3 different pc''s with varying video cards, to my utter surprise the dots appeared just like they did on my pc. I then concluded it wasnt a hardware problem after all but just a glitch or error in the software. I asked this in another forum and someone who responded (who sounded pretty informed)that this is a well known issue in many of todays games and is most definitely not a related to hardware at all. Could you explain what exactly this is and why it happens in some games?? Is their a term for this and are their any articles or sites that might have more info on this? Its kinda driving me nuts because since I started noticing them, everytime I play a game I find myself looking for them. I just dont remember seeing them in the past or maybe its just I really never noticed them. If you can help explain this, I would greatly appreciate it!!! Thanks so much.

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If you're talking about what I'm thinking, the problem is non-standard texture coordinate centering. Nvidia cards in particular suffer from this problem.

Basically, "most" cards work on the idea that the texture coordinate 0.0 is the _center_ of the upper left pixel in the bitmap and 1.0 it the _center_ of the lower right pixel in the bitmap. Unfortunately, Nvidia seems to do it so that 0.0 is the upper left corner of the upper left pixel in the bitmap, and 1.0 is the lower right corner of the lower right pixel. Obviously, this means that texture coordinates are non-standard between cards. Lovely isn't it? In fact, to compound matters, Nvidia even lets you shift the texture coordinate values through driver control panels. A great example of giving users control over things they should never be touching.

Its a pretty insane implementation, but there you have it. Nvidia cards have had this problem since before the TNT 1.

The fix is easy, but annoying to have to do. You just need to shift your coordinates by 1/2 texel (so, the shift is dependant on the width/height of your texture) to account for the difference. And if the user has played with his settings? Well, you're kind of screwed.

Edited by - daveb on October 5, 2000 12:04:37 PM

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Thanks for your explanation though I really dont understand alot of it. Anyway your saying it can fixed using the "texture alignment" slider in the Nvidia control panel? I think I tried every setting their and I dont remember it helping. Like I said I tried a couple different geforces on my pc and even a Voodoo 5500. Dots were still there, and I also played the games on different pc''s at work, one with a Voodoo card and the others with Matrox''s cards and the dots appeared just as they did on my pc. Any other ideas..

Here are a short list of games I have seen these in
Motocross madness 2
Midtown madness 2
Breakneck
Unreal tournament
Crimson Skies
and others

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Guest Anonymous Poster
It sounds just like simple polygon seaming problems, which are VERY hard to get rid of entirely. What happens is that floating-point imprecision and rounding errors cause the slopes of two edges that are SUPPOSED to meet to be slightly different when they get to the rasterizer. What you are seeing are the pixel-sized gaps that result from drawing two lines that are ALMOST parallel. Usually what''s IN the gaps (behind the polys being drawn) is not pleasing to the eye. Probably every 3D game ever made has some sort of seaming problems somewhere. As we get into higher and higher video resolutions for games there will be less quantization in the rasterizer and you''ll start to see the problem less.

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Your explanation Anynomous sounds similiar to what another gentleman told me. What really freaked me out over the whole thing was I just dont remember seeing them in the past with older games now I notice them in alot of the new games I have bought. Some don''t seem to have them and others(especially games with vast open areas)you can easily spot them in the "seams" between two textures. Granted they are small but the way they pop up and disappear annoys the crap outta me. I have showed some friends of mine this and at first they dont even notice them, but when I point them out, they can plainly see them. In Midtown madness 2 you usaully see them in the large grassy areas and in the seam where two buildings meet. I just want to know for sure that this is normal and that its not something to do with my hardware.

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I doubt you''ll find any "articles" online about this. I think the previous responses have done a fine job of describing the problem, and the only way for you to understand it any better is to study Ye Olde Art of 3D Graphics. However, if you''ve got some spare cash I can recommend an excellent book that will both answer virtually any 3D graphics questions you may have, and happens to have a pretty good description of this problem. It''s called "The 3D Graphics Programming Black Book" or something like that by Michael Abrash.

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Actually there are articles about this. In fact, there are links for them on this site. Check out the 2 articles on "Sub-Pixel Accuracy" and "Sub-Texel Accuracy". They explain why it happens and how to avoid it (in your own games).

David

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I appreciate the responses. I tried searching for the articles you mentioned and found a few I think pertain, I say think because most of what was written was beyond my me. If anyone can explain this in simpler terms It would help. I am curious because I dont rememder seeing these "dots" in games before, but if they are normal maybe I just never noticed them and now that I have seen them, I find myself maybe looking for them. They are very tiny but they are pretty noticeable which makes me wonder why more people dont complain about them? In some games, their not there at all, in some games just here and there and in still others there very prominent. I swore it had to be a hardware or driver issue but after seeing them in the same games on several different pc''s , I realized they werent. Does anyone know if the texel alignment setting on a geforce cards driver control panel could atleast somewhat aleviate these "dots". Its at the default setting now. Thanks

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I''m using an ATI card and I have ''em too. The only game that I''ve seen them in is Motocross Madness. I guess the reason that you haven''t seen them in the past, but are seeing them "now"(in the last couple of years), is because then number of polygons have gone up. That''s also probably why you see them in games with large open areas, they''re more polygons in larger areas. And also the a lot of the polygons are "farther"(meaning the Z value is higher) away from you so the math is less precise. That''s the only thing I can think of. Then anon poster said something about as resolutions go up, you''ll see less of them. Maybe try playing the games at a higher resolution (800x600 instead of 640x480 maybe?). Hope your search for inner peace and a rested state of mind about the issue comes to a happy conclusion.



"We are the music makers, and the dreamers of the dreams."
- Willy Wonka

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Can you show us a screen shot? I''m thinking you may be talking about the textures you sometimes see through other textures due to the presision lost on the Z-Buffer calculation.

An example is when you''re in a FPS game. If you zoom in on someone that''s really far away and behind a wall, in somesituations, you can see him due to the Z-Buffer precision loss.

For now, you just have to live with it.

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