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Cypher19

Some question about shadow maps/buffers

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Recently, I saw Carmack's QuakeCon speech, and one thing that I found was that John obviously wants to go to shadow maps. Now, I can't find a lot of up-to-date info about them, but I was wondering about a few things in particular: 1) For the multisampling technique described, would this decrease/eliminate the 'aliasing' that current shadow maps have? 2) Similarly, would the multisampling allow for very crisp shadows at short caster-to-shadow distance and also do blurred shadows at longer distances, such as in real life? 3) He keeps re-itereating the need for ultra-high-resolution shadow maps, on the order of 2000x2000. Even with the dynamic scaling he came up with, won't this be VERY old-hardware unfriendly? A lot of people were upset enough that they had to upgrade their computers further for Doom3, but if textures of that size are required, even more modern cards like the GeForce4/Radeon8000 would be absolute sloths in that kind of scenario. 4) How does it compare to other soft shadow algorithms such as the closely related Unreal Engine 3 solution and Akenine-Möller/Assarsson's solution in terms of expected performance, image quality, and disadvantages? Thanks in advance for your time in answering the questions.

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1. Decrease it a bit, maybe, but eliminate it.. no.

2. That's possible, but you need a high amount of samples to get a good blur. You are starting to get reasonnable results with 8 samples, but 16 is better. Performance drops dramatically. If in addition you need to compute a "crispness" factor per-pixel, dependant on the pixel-to-occluder distance, i doubt you'd get very real-time framerates.

3. What do you call "old-hardware"? All the Geforce and Radeon series support at least 2048x2048. And don't forget that when rendering to a shadow map, you're only rendering to a ZBuffer, so it's a lot faster than rendering to a 2048x2048 color buffer with textures and shaders.

4. There is no soft shadows in Unreal 3, at least not "accurate" soft shadows like described in your link. It's using tricks - basically, interpolating between a static sharp and a blurred cube map and projecting it onto the environment.

Y.

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Old hardware I define as GeForce3/Radeon 8000 and earlier (since according to hardware surveys such as the one at www.steampowered.com over half of the people participating have an equivalent or better one). But when I'm concerned about the size of the shadow map required, I'm mainly talking about fill rate and memory limits.

Anyways, thanks for your response.

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