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D3DX Util, Voodoo2 and strange effects


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#1 AntonyHirst   Members   -  Reputation: 122

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Posted 09 February 2000 - 12:32 PM

Hi, When rendering with my Voodoo 2 (SLI) I am getting whole polys (and groups of) appearing and disappearing. I can move 1 meter forward from getting an entire scene suddenly on the next render half the scene disappears. 1) In an effort to fix this I have turned off the Z-buffer, any fancy hiden sruface so that I am rendering every polygon in the scene. However, the effect remains. 2) I have placed assertions everywhere so that I know the database is in the correct state. 3) I know the polys are being passed to DrawPrimitve 4) I have no problems at all on my Primary 3D cars (a Cirrus Logic slow thing) in HAL mode. Could it be a quick of initialising with the Direct3DX library? Many thanks, Tony

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#2 mhkrause   Members   -  Reputation: 122

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Posted 09 February 2000 - 12:44 PM

I''ve used D3DX with a Voodoo 2 before, and experienced no problems.

Do the D3DX samples work fine on your Voodoo 2?

#3 Spellbound   Members   -  Reputation: 122

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Posted 09 February 2000 - 12:47 PM

It sounds like you''ve discovered a bug in 3Dfx DX drivers that has to do with SLI. It seems the second card don''t get the polygons it should render.

Have you tried to use the reference rasterizer?

#4 AntonyHirst   Members   -  Reputation: 122

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Posted 10 February 2000 - 06:59 AM

Hi again,

The samples work fine. This is why I''m confused. It must be something I am doing wrong as I just noticed that I get glitches in the primary card too but only in fullscreen. In windowed mode my prmary card is perfect!!

Why would a polygon (or groups of) be ignored by the card. It can''t be the FVFs (all polys would be wrong then) or the textures (I turned them off). No z-buffer (i turned that off too). Could it be my back buffer count? The number of Alpha bits?

In my experiance when things get this bad it is usually a silly mistake or a stupid assumption. I just can''t get my head round what it could be.

Many thanks,


Tony

#5 Esap1   Members   -  Reputation: 122

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Posted 11 February 2000 - 02:23 PM

THATS Funny, Im using Voodoo2 SLI with Dx Util, in DX7, every thing works fine. Little slow when close to polys, because of the low fill rate, but Other than that, it works great, if you cant get it to work, Ill give u my setup code, later

#6 AntonyHirst   Members   -  Reputation: 122

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Posted 12 February 2000 - 01:03 AM

Thanks, I''d like to see your setup code, it may be a great help. Popit along to antonyhirst@bigfoot.com.

Cheers mate,








Tony

#7 evaclear   Members   -  Reputation: 162

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Posted 12 February 2000 - 07:53 AM

WOW you got that peice of junk wrapper to work on a Voodoo 2? Impressive! Any of the demo applications refused to work when I had a Voodoo2, and I''ve heard other people complain of the same problem. I keep my drivers quite up to date, so I know that''s not the issue. However from my experiance with it, I consider D3DX to be highly unstable and unsutable for a commercial product. But that''s just me.

#8 AntonyHirst   Members   -  Reputation: 122

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Posted 12 February 2000 - 01:26 PM

Funny you say that because I have been pondering giving up on the D3DXContext and am rewriting the initialisation stuff in long-hand.

I can get D3DX to recognize the Voodoo2 SLI but there is something fundementally wrong with the rendering. It is either me or D3DX. Either way I''ll find it by getting back to the heady and glamerous world if enum functions (sigh!)


Tony

#9 AntonyHirst   Members   -  Reputation: 122

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Posted 12 February 2000 - 01:28 PM

BTW, I forgot to say that I get no problems on any card with aprox 1-2 thousand polys. It goes pear-shaped at about 10,000+ polys.


Tony

#10 Esap1   Members   -  Reputation: 122

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Posted 13 February 2000 - 12:32 AM

It works in other DirectX apps, and not yours, funny, mines workin great!

#11 AntonyHirst   Members   -  Reputation: 122

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Posted 13 February 2000 - 05:24 AM

Errm,

I know it works in other apps. How about that offer of the code sample so I can see why it doesn''t work in mine.

Tony

#12 AntonyHirst   Members   -  Reputation: 122

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Posted 14 February 2000 - 07:41 AM

Problem bl**dy solved!!

Right then. After reading the documentation and applying common sense I assumed the following process.

1) Initialise
2) Render Loop
3) Clear Z-Buffer
4) Render Object
5) Get Next Object
6) Goto 2 until no more objects
7) Flip surface

What I actually needed to do was:
1) Initialise
2) Clear Z-Buffer
3) Render Loop
4) Render Object
5) Clear Z-Buffer
6) Get Next Object
7) Goto 3 until no more objects
8) Flip surface.

Why you need to clear the Z-buffer before flipping is just a mystery to me. Expecially when the Z-buffer is turned off!!!





Tony

#13 Anonymous Poster_Anonymous Poster_*   Guests   -  Reputation:

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Posted 16 February 2000 - 06:35 AM

Sounds like what you are describing is Z-Fighting. Polygons that are fairly close will sometimes screw up visually because the Z-Buffer precision isn''t high enough for the closely lying polys.

There are ways to help solve this (use 32 bit zbuffer, use wbuffers (for some types of scenes), changing the near and far clip planes) etc. etc...

I would recommend going to NVidia''s site and read the articles there about Z-Buffering/W-Buffering...


#14 AntonyHirst   Members   -  Reputation: 122

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Posted 16 February 2000 - 07:29 AM

Thanks for the reply,

However, I don''t see how the requirement to clear the z-buffer after the final render and before the flip has any effect on near plane precision problems. A very import and strange point is that I would have the problems with the z/w-buffer switched off and the also with the w-buffer switched on.

If you are not convinced by that, I also reduced my projection matrix planes from 0.1-10,0000 to 1-300 to make remove any doubt about z precision.

Now that I do clear the z/w-buffer after the last render and before the flip I get a perfect render.

It looks bootiful!

Tony.

Tony




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