How do you display shadows on invisible surfaces

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Shadows on invisible models should be possible by using nontransparent models with an FFP effect that renders only into the z buffer, but nothing to the screen buffer. I haven't tried it, though.

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That quote came from this thread:

http://www.coniserver.net/ubbthreads/showflat.php/Cat/0/Number/747240/

It's an entirely different subject involving a request to place panels behind the view and has since been implemented into the newest private beta (thanks jcl); however these two features are related.

In a 2.5D game, the backgrounds are either prerendered or made by hand (drawn, painted, etc). The player and NPCs; however are realtime. In order to interact with these 2D backgrounds, an invisible, 3D collision hull has to be constructed and has to match the background. If there are two wooden crates in the middle of the screen, you have to place a collision block there so the player won't walk through the crates. There is also some layer_sorting effects that have to be done, but that's beyond the scope of this thread.

Anyway, using that crate example above, let's say the player's stencil shadow covered the crates. Since 3DGS won't allow the shadow to appear on my invisible collision geometry, it's not going to look right. If the feature were implemented, the shadow would wrap itself around the crates just like they would in a full realtime game. It's a fancy pants illusion, and according to jcl (see above), it can already be accomplished.

Here's a screenshot from the Resident Evil remake on Gamecube. You can see the player/zombie shadows going up the wall on the left. This is a prerendered background, so there is invisible collision geometry in place and the shadow is contouring to that and when combined with the 2D plate, the illusion is complete:



This is where I need help. Using jcl's comment or using a different method (if you know of one), I'm requesting that someone help me out with writing this particular effect. Thanks.

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Shadows on invisible models should be possible by using nontransparent models with an FFP effect that renders only into the z buffer, but nothing to the screen buffer. I haven't tried it, though.

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Hi Ryan,

the hidden geometry indeed needs to be rendered into the depth buffer, so that the shadow volume is properly mapped onto it. In Direct3D the following render states should do the trick:

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m_Device->SetRenderState(D3DRS_ALPHABLENDENABLE, TRUE);
m_Device->SetRenderState(D3DRS_SRCBLEND,  D3DBLEND_ZERO);
m_Device->SetRenderState(D3DRS_DESTBLEND, D3DBLEND_ONE);

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This unfortunately also means the hidden geometry must closely match the 2D image, otherwise the depth buffer will mask the 3D character (like on this screenshot: http://www.dead-code.org/blog/wp-content/shadow2.png).

JN

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But I'm still wondering why you won't use the sprites as hand drawn art together with the stencil shadows

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What do you mean by this? How is the stencil shadow going to interact with a bitmap and contour to it's details? It can't which is why the invisible collision hull must be in place and anyplace the player's shadow can touch much closely match the 2D sections.

Here are a couple of quotes from a very famous adventure game artist/designer working on the adventure game A Vampyre Story. They're using the exact same technique I'm stealing from them. Perhaps, his explanation will be better. There are two of them taken from two different posts:

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So AVS will be in 3d BUT,,,,not the way you think. I am a big fan of the early Disney movies, and one Oscar winning short in particular really influenced me. It was called The Old Mill. http://disney.go.com/vault/archives/movies/oldmill/oldmill.html It was mood film, meaning it didn’t really have plot, but for good reason. It was a test film for a new technique called multiplane camera. So we are going to do is make a virtual multiplane camera using your PC’s 3d card. The backgrounds will be painted in 2d but placed on 3d planes. This will allow us to keep the backgrounds looking 2d and hand painted, but we get to create the illusion of depth and perspective.

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We draw the backgrounds on paper then scan that in and paint the set layers in Photoshop, with each plane on its own separate PSD layer. Then we save the separate layers as TGAs (Targa files) and turn them into textures, along with their alpha channels (transparent matted areas) in Maya, and then UV map the layers on to flat parallel polygons in Maya. Export that file into our engine, test it make sure it works. Then add particle affects and UV scrolling areas. Add the dynamic lights for the sets and 3d Character models. Import a separate set of geometry for the walk boxes, test that out. Then add all the interactive objects like doors and buttons and things like that. We use Maya to build the character meshes, rig them and to animate them. Nothing really exotic in this process. They only thing unusual is that we aren’t building 3d models for use as our sets, just 2d planes.

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@ OB:

Well, I see your problem and the quote you've copied expains how it can be achieve in theory. The practical side is quite more complex I guess. A plugin like I mentioned could be the answer. Like HeelX suggested, SMEE2 could be a potential solution. I will keep on testing with the shadow mapping shader, if you might need it, just ask. Because of the faqt that you can't integrate any other solution, a shader could be the only option... But this is someting we'll see later on in the future

But to refer to your question:

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What do you mean by this? How is the stencil shadow going to interact with a bitmap and contour to it's details? It can't which is why the invisible collision hull must be in place and anyplace the player's shadow can touch much closely match the 2D sections.

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What I ment by this, why not just a simple sprite that represents your art.
Then set the shadow_stencil var to on where as the shadow will interact (contour) with your scene (geometry blocks,sprites, models). Here's a picture where I simple programmed the shadow_stencil veriable in c-script to on and setted the shadow flag and the cast flag in wed for the model. The green sprite hasn't got anything attached qua action or flag:


@ HeelX:

Good luck

Cheers

Frazzle

Nice results HeelX, OB will be quite pleased so far
The mesh problem is like Mnemonic at Wintermute mentioned:

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This unfortunately also means the hidden geometry must closely match the 2D image, otherwise the depth buffer will mask the 3D character (like on this screenshot: http://www.dead-code.org/blog/wp-content/shadow2.png).

JN

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I guess this can be resolved with the methode OB is trying to use and the quote I copied. Just place the parallel planes at the right position which match the position of the invisible scene where than the hand drawn art will be mapped on those planes and OB his problem should be resolved

Cheers

Frazzle

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Hi Ryan,

the hidden geometry indeed needs to be rendered into the depth buffer, so that the shadow volume is properly mapped onto it. In Direct3D the following render states should do the trick:

Code:

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m_Device->SetRenderState(D3DRS_ALPHABLENDENABLE, TRUE);
m_Device->SetRenderState(D3DRS_SRCBLEND,  D3DBLEND_ZERO);
m_Device->SetRenderState(D3DRS_DESTBLEND, D3DBLEND_ONE);
 

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This unfortunately also means the hidden geometry must closely match the 2D image, otherwise the depth buffer will mask the 3D character (like on this screenshot: http://www.dead-code.org/blog/wp-content/shadow2.png).

JN

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The red part is how it would be setted within D3D which is identical qua functionality to the code snippet HeelX posted. I've read about information that zEnable, zWriteEnable,alphaTest and alphaBlendEnable won't make any difference. Here's the information from msdn regarding render states:

msdn link

To make this error dissapear, you'll have to 'cheat' towards realtime rendering That is the only option AFAIK to resolve this problem until now. Maybe shadow mapping or shadow volumes via shaders won't be affected by invisible scene geometry but on the other hand, OB wants to avoid the shader way but I'll give it a shot though

Cheers

Frazzle

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This unfortunately also means the hidden geometry must closely match the 2D image, otherwise the depth buffer will mask the 3D character (like on this screenshot: http://www.dead-code.org/blog/wp-content/shadow2.png). />

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Given my semi-technical mind (from a programmer's POV), this is all a bit overwhelming, but I get the gist of it.

The entities that should be casting stencil shadows are the player or any other NPC. Any hidden geometry for the Background/foreground scenery (the level) shouldn't be casting anything in a pre-rendered/hand drawn background. I noticed in Heelx's screens that the cube seems to be casting what appears to be a stencil shadow when only Mr. Warlock should.

Anyway, I think the issue is slowly or has already been resolved (not sure yet ). It's kind of nice to see some of the greater 3DGS programming minds working on this if for nothing more than to tackle the challenge of it. I'm not sure how many of you would actually use it, but I guess I sparked some inspiration.

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Btw, the problem HeelX had, could also be solved via a sprite which should match the geomety of the scene. This is the methode OB original wanted ^^

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Finally, is it possible in DirectX to make an invisible model cast a stencil shadow and if so could you add this to the todo list, too (assuming it isn't already possible...I'm away from my regular PC, so I can't check).

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You already can use, or even already use normally, the LOD of your charcter for the shadow in A6.
Just picked up this sentence, so it can be that this already had been mentioned.

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