XNA Framework

Re: Avatars and shadow maps

gustav — Sun, 26 Jul 2009 19:10:20 GMT

The problem with shadow maps and avatars is that even if you manage to render the depth in some way (dummy model, center-plane-depth), you'll not be able to do self-shadowing since it requires depth tests when rendering the
actual avatar. Combining a dummy model (that has thicker geometry than the avatar) and the stencil buffer (as jwatte said) would produce quite good results though. Always rendering the dummy model depths while using a stencil mask created by solely the avatar to render the avatar parts of the depth maps / final comparison map.

I didn't see any self-shadowing in X-tatic's screenshot but this might be what he is doing/planning to do though :P

Re: Avatars and shadow maps

Venom WKB — Sun, 26 Jul 2009 11:38:51 GMT

XTatic:
Just thought I'd chime in here and say that shadow mapping with avatars IS possible, with a trick or two:
http://www.x-tatic.net/images/AvatarShadowMapBox.jpg

Could you please explain the "trick or two"? ;)
I think i understood you used a fake avatar model, but what else?

Did anyone noticed that in the "1 against 100" beta testing avatars have soft self shadows? :s

Re: Avatars and shadow maps

Danny Tuppeny — Fri, 24 Jul 2009 21:33:13 GMT

UberGeekGames:
Aren't we past the N64 era (Wii-era too, actually) of circular darkened quads stuck to the feet of our characters? ;-)

This worked fine for World of Warcraft for almost 4 years :-D

Re: Avatars and shadow maps

VengantMjolnir — Fri, 24 Jul 2009 17:57:33 GMT

I suppose you could use this technique to implement stencil volume shadows as well, that would give self shadowing. I wonder if the hard edges of the shadows though would make it more obvious that the shadow caster is a stand-in. I don't suppose there is a way to get access to the geometry of the avatar for creating the shadow volumes eh?

Re: Avatars and shadow maps

XTatic — Thu, 23 Jul 2009 07:27:15 GMT

Just thought I'd chime in here and say that shadow mapping with avatars IS possible, with a trick or two:

http://www.x-tatic.net/images/AvatarShadowMapBox.jpg

Re: Avatars and shadow maps

Ultrahead — Sun, 05 Jul 2009 23:09:30 GMT

It's not the method described by Jon but it could work ok for simple games:

http://amapplease.blogspot.com/2009/07/xnavatars-part-2-no-shadows.html

Re: Avatars and shadow maps

jwatte — Mon, 15 Jun 2009 18:52:02 GMT

You can flatten the avatar and render to a stencil map to get an area of "stuff to shadow" if you want. In fact, you can render your depth map that way:

0) from the point of view of the light
1) render to stencil buffer, setting any pixel touched by avatar
2) re-render, writing a "central" depth to a render target where the stencil buffer is touched (typically the plane through the center of the avatar)

This doesn't give you self-shadowing on the avatar, but it does give you depth shadows on anything beyond the avatar.

Re: Avatars and shadow maps

Barkers Crest — Mon, 15 Jun 2009 18:17:44 GMT

UberGeekGames:
Shawn Hargreaves:

To cast shadows from an avatar onto the environment, depth based shadow maps are out, but you could use an ID based shadow map.

So what would be our options for casting shadows from Avatars onto objects?

I mean, this is the Xbox 360. Aren't we past the N64 era (Wii-era too, actually) of circular darkened quads stuck to the feet of our characters? ;-)

My plan is to build a dummy avatar model and use it for shadow mapping. The shadow will not be 100% accurate but I think most people won't be able to tell.

I do have a game I'm working on that does use the circular darkened quads for shadows ( Not avatar related ). They look good too. :)

Re: Avatars and shadow maps

Nick Gravelyn — Mon, 15 Jun 2009 17:47:32 GMT

Sowaz:
Wait, why are depth-based shadow techniques out for having avatars cast (not receive) shadows? As long as the avatar writes to the depth buffer when rendered, it seems like you would have all you need. Though perhaps I need to brush up on my shadow mapping algorithms?

Because you have no read access to the depth buffer, so there's no way to get that depth information. To implement shadow maps you normally render the object's depth (using your own pixel shader) to a render target. Since you can't use custom shaders with avatars, such approach is not possible.

Re: Avatars and shadow maps

Sowaz — Mon, 15 Jun 2009 17:35:22 GMT

Wait, why are depth-based shadow techniques out for having avatars cast (not receive) shadows? As long as the avatar writes to the depth buffer when rendered, it seems like you would have all you need. Though perhaps I need to brush up on my shadow mapping algorithms?

Re: Avatars and shadow maps

Shawn Hargreaves — Mon, 15 Jun 2009 17:18:31 GMT

UberGeekGames:

So what would be our options for casting shadows from Avatars onto objects?

ID based shadow maps are the most practical option I can think of.

But yes, you do lose a lot of control over rendering and shading when you decide to use avatars. The avatar system has more of a cartoony graphical style, which is great for some games, but not so appropriate for others that are going for more realistic character models and lighting.

Re: Avatars and shadow maps

UberGeekGames — Mon, 15 Jun 2009 16:53:03 GMT

Shawn Hargreaves:

To cast shadows from an avatar onto the environment, depth based shadow maps are out, but you could use an ID based shadow map.

So what would be our options for casting shadows from Avatars onto objects?

I mean, this is the Xbox 360. Aren't we past the N64 era (Wii-era too, actually) of circular darkened quads stuck to the feet of our characters? ;-)

Re: Avatars and shadow maps

Shawn Hargreaves — Mon, 15 Jun 2009 16:45:52 GMT

Avatars don't support custom shaders, which includes shadow maps.

To cast shadows onto an avatar, stencil shadows should work ok, but I don't think shadow maps are possible.

To cast shadows from an avatar onto the environment, depth based shadow maps are out, but you could use an ID based shadow map.

Avatars and shadow maps

CosmicFlux — Mon, 15 Jun 2009 16:38:44 GMT

Looking through the docs for the Avatar support, I can't see the support for self-shadowing maps. Am I looking in the wrong place?

Also, I can't see how you are supposed to be able to render the avatar to a shadow map that would be used for the rest of the scene - is this even possible?