Oh no... It's catching... I've just had the same stroke....Originally posted by knackered:
Have I had a stroke or are you lot talking in some kind of foreign language?
Oh no... It's catching... I've just had the same stroke....Originally posted by knackered:
Have I had a stroke or are you lot talking in some kind of foreign language?
Scott S.
www.southurst.id.au
lol Sorry, but this way we could understand eatch other better.
Portugal! Not Iraque. We're speaking portuguese (one of the most beautifull languages on the planet).
Pedro: Não existem muitos sites sobre GL em portugues, embora na minha pagina tenhas lá algumas coisas (está no meu info). Dá-me o teu mail e mando-te uma implementação de shadow volumes....
IMHO the easiest way is to use shadow maps.
Unfortunatly they have a ton of artefacts that you can't really do anything about.
Also when you have a light and shadow at a very small angle you get huge ugly jaggies . Supposedly you're able to reduce these by rotation , but that isn't what I've found.
Woo has an improved variation of shadow maps. But even with rotation it still can't handle situtaions where the light angle with a surface is small.
In case you're thinking I just implemented these algorithms incorrectly I'll point out all of these screenshots are from nvidia's samples.
I originally avoided stencil shadows because they have so many errors when self shadowing. Unfortunately I wasn't paying enough attention to the nvidia examples , because they have just as many (different) problems . They look great with the default view, but when you zoom in or put the light at a non optimal position you get a ton of artefacts.
With stencils you simply get incorrect shadows.
Has anybody found a way to reduce these artefacts?
Damn, Geocities is a PITA.
If you want to see those pictures showing various shadow map artefacts you'll have to load the web page as it seems you can't link to a picture.
I'd still love to hear if anybody has solutions for either the robot or the small light/surface angle problems. They really do limit shadow maps usefulness.
The page doesn't work either!
I'd argue that in most cases stencil shadows are better if all you need is "correct" shadows for depth hints or so. Shadow maps can be plugged in more easily, but with all their problems, I wouldn't call them easier. There are hacks aroud most of them though.
But if you want realism or athmosphere, softness matters more than correctness, and that's where the shadow maps start to rock.
Jittered soft stencil shadows are likely to be the first shadowing algorithm that doesn't suck, but that's still out of reach when it comes to complex scenes and lighting. So it's a tradeoff you wouldn't want to make...
-Ilkka
I have seen problem with shadowmaps, but not that much.. use offset when creating the shadowmap to lift it a small bit in the Z and you should be able to tweak awat some of those errors.
The page should be working now. The biggest drawback, IMHO, to stencil shadows, is the way shadows pop on or off. Check out the knight's shield on the bottom of that page (screen shot also from nvidia's cg broswer 5.0). They really don't work well for self shadowing either.Originally posted by JustHanging:
The page doesn't work either!
I'd argue that in most cases stencil shadows are better if all you need is "correct" shadows for depth hints or so.
-Ilkka
The 2nd drawback is they are a bit more diffuicult to implement than shadow maps.
The problem is no matter what I can't seem to get rid of the errors. I can tweak away for a given scene until it looks perfect.Originally posted by Mazy:
I have seen problem with shadowmaps, but not that much.. use offset when creating the shadowmap to lift it a small bit in the Z and you should be able to tweak awat some of those errors.
Then I'll move the object or light and I'll see artefacts. So I'll tweak those away. Then I go back to the first light/object position and I see it has artefacts again!
This tricked me into using shadow maps. I thought I would be able to tweak artefacts away for any scene. This is really only sort of possible if the scene is static!
In the second depth paper (bottom of 1st column, 2nd page) Wang and Molnar come to basically the same conclusion I did, you can't just tweak away the artefacts in your scenes.
If you think you can I challenge you to try to fix those nvidia samples.
(don't take the challenge to seriously, I think shadow maps simply don't yet work)
The easiest way to get rid of that (mostly) is to use a form of per-pixel lighting, so that as the light source goes past a surface, it fades out and is near black (or whatever your ambient lighting is) by the time the shadow "pops" in.Originally posted by titan:
The page should be working now. The biggest drawback, IMHO, to stencil shadows, is the way shadows pop on or off.
At least with stencil buffers, you can have phisically more realistical shadows. I means that you do not highlight everything and then put black/gray pixels where shadows should appear. You instead noly hilight only the exact area that can receive some light.
Shadow maps are said to be easier to blur/make soft? So what? In most case it is just an image based technic, not a geometry based technic, so it does not take into account the distance from occluders so it's not realistical.
I don't have any problem with self-shadowing. Do you use a planar silouhette? When generating a volume from the 3d edges, you don't have such problem.
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