*Sub-Thread* Dithering in GTA4

Discussion in 'Console Technology' started by Laa-Yosh, Apr 28, 2008.

  1. Shifty Geezer

    Shifty Geezer uber-Troll!
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    By this response I presume the guy is talking about the uniform texture dithering, and not the texture noise, which is something else entirely, but which people aren't differentiating between in conversation despite the noise (not the dithering) being the reason for this thread!
     
  2. Mize

    Mize 3dfx Fan
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    Good point...I can see the dithering you're talking about as an artistic choice (not one I'd make probably), but certainly not the noisy - garbled stuff that this thread seems focused on.
     
  3. wco81

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    PS3 can't handle dithering? Uh-oh, it's going to hit the fan.
     
  4. liolio

    liolio Aquoiboniste
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    Would be fun to hear Rockstar about this.
    It's likely that they did it because they thank that overall it fitted the game better (according to theirs tastes).
    Now with all the noise around the effect (.... :lol:) they might really question theirs tastes and feel lone.. :lol:
     
  5. MazingerDUDE

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    Wow, does it mean that they wasted performance to get this dither effect in 360?! like they chose the dithered textures over a better frame rate? That's got to be the stupidest decision anyone could ever make :lol:
     
  6. speedsix

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    It's seriously unlikely Rockstar would ever fix this issue though, right? I mean, why would they bother.
     
  7. chachi

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    There are two things going on. Maybe. :)

    The grainy 'dithering" seems obviously some shader effect, that's the artistic decision and whether it costs performance depends on other factors. Maybe they were CPU constrained and had some "free" GPU cycles so they chose to implement that effect.

    There's also the noisy textures (most of the closeups deal with this, an example is the text on the Burger Shot sign) that is what this thread mostly is about. It's remotely possible this is a side-effect of the above, there is some serious break-up issues involved with alpha values on textures (e.g. the billboard where big chunks of the under-structure is blasted away) but even relatively close up you can see an exaggerated noise on the text of small textures and that shouldn't be happening to that extent, so it's probably something else. Maybe they do an initial grain on the texture when they generate the mipmap variants to get it to blend better with the environment, and then it gets an extra dose with the grain shader and that's why it's so ugly.
     
  8. paawl

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    Thanks, Rockster! I didn't realize there was audio available for that presentation. I listened, and right at 28 minutes and 26 seconds the presenter says that, "another thing to keep in mind is that any DXT compressed textures will be uncompressed when they're brought into the texture cache".

    I always thought that GPU caches stored textures in compressed form, at least since NV20, but I guess that might have been an nVidia-only optimization. Does anyone know what ATI's PC GPUs do in this regard?
     
  9. ErnstH

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    Maybe nVidia patented that brilliant idea. :wink:
     
  10. Jawed

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    Until R600, ATI GPUs have only had a 1 level texture cache.

    It would appear that texture decompression is performed before texels are placed in Xenos's texture cache.

    My understanding of the two-level cache approach is that texels are decompressed on their way from L2 to L1, meaning that L1 holds decompressed texels.

    Jawed
     
  11. Simon F

    Simon F Tea maker
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    Intriguing. That's quite the opposite way to how I would have a texture cache function. <shrug>
     
  12. nAo

    nAo Nutella Nutellae
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    IIRC previous ATI architectures always assigned a single pixel pipe to predetermined screen tiles so that a L1 per pipe can probably cover the texture(s) working set on a per tile basis. A L2 on top of that would have been nice though :)
     
  13. Jawed

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    This is the two-level cache architecture:

    Two level cache memory architecture

    Looking at figure 5 (which shows a single quad texture fetch/filter pipeline) you'll see that each L1 cache contains four instances of memory (each described as 2KB in size) corresponding with the locations of texels in the texture.

    Unfortunately I can't find mention in this document of decompression. I surmise that decompression happens twixt L1 and L2 merely because L1 provides per-texel locality for feeding data to the filtering pipes.

    I have to admit, reading this:

    3-D rendering texture caching scheme

    and considering that the base design for R600 is fp16 texels (which aren't compressed) I'm now thinking that decompression is performed for DXT etc. before the texels are put into L2.

    Jawed
     
  14. Simon F

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    What I meant was, caching raw memory (i.e. compressed textures) VS decompressed 8888 means that your texture cache effectively becomes 4~8x larger. <shrug>
     
  15. Jawed

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    Hmm, yeah, Xenos is stuck with the kind of texturing that RV610/620 have (no L2 at all).

    Jawed
     
  16. Jawed

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    Yeah, I took that as read. It appears as if, historically, ATI's been averse to building multiple copies of decompression units per quad-texturing unit.

    Jawed
     
  17. Droid

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  18. speedsix

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    GTA has had an auto-update on both platforms. The shadows look softer and less grainy to me but I could be talking nonsense.
     
  19. DrJay24

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    G4 said it was a MP patch for stability online.
     
  20. speedsix

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    There were single player changes aswell
     
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