projected shadow alpha problem

Hello,
we've worked out a very naive polygonal shadow projection script by simply projecting the mesh on a receiving surface. We're using the following shader to render the shadow:

Code (csharp):

1.  
2. Shader "MVStudios/ShadowShader" {
3.     Properties {
4.         _Color ("Color Tint", Color) = (1.0, 1.0, 1.0, 1.0)
5.         _MainTex ("SelfIllum Color (RGB) Alpha (A)", 2D) = "gray"
6.     }      
7.        
8.     SubShader {
9.         Material {  }
10.            
11.         Tags {"Queue" = "Transparent"}
12.         Lighting Off
13.         Cull Back
14.  
15.         // Rendering pass
16.         Pass {
17.             ZWrite Off
18.             ZTest Less
19.             Blend SrcAlpha OneMinusSrcAlpha
20.             Color  [_Color]
21.             SetTexture [_MainTex] {
22.                 Combine texture * primary, texture
23.             }
24.         }
25.     }
26. }
27.  

As you may see in the picture the problem we have is on overlapping triangles, where the rendered alpha value is not correct. Any help will be appreciated.
Thanks.

E.

 

So there's no way to make the CharacterShadow script semi-transparent?

 

One workaround would be to render the character all black and then use a 2nd combiner state to fade it back up towards white.

 

You've attained the classic GameStudio look!

 

That's exactly how the shadows in Quake 2 engine games were done. And yes, they have the same problem. So it was good enough for commercial games...of course, Quake 2 is slightly outdated these days....

--Eric

 

Thanks everybody. :wink:

E.

 

Hey bytescruncher,

Just curious if you'd be willing to share the other half of this techinique with us?

Thanks,
Ethan

 

hey.. quake 2 rocked my world

actually i still love firing up quake 1 every now and then, i absolutely love the look and feel that engine has

 

Hello Ethan,
sorry for getting back to you so late. This technique is very straight forward.
I enclose a very naive script that makes the trick. I wish I could upload it onto the wiki site, but was unable. Maybe some of you guys will be so kind to do that.

1. Prepare a lower resolution mesh and skin it like your original model (the one casting the shadow).
2. be sure your shadow mesh move along with the original one.
3. attach the script I enclose to the original model.
4. assign to a receiving plane a user layer (by default #8 )
5. set the script properties (what light casts the shadow, the shadow's mesh, and the layer where the receiving objects lie).

This technique basically projects each vertex of the shadow mesh onto a receiving mesh (ideally a plane). It has some limitation but it works nicely if you need to project the shadow on a nearly flat surface and you can live with an opaque shadow (or live with the artifacts highlithed above if semi-transparent).

The projection is made by drawing a vector from the light to the receiving surface, through the shadow's vertex. Despite its semplicity this might come in handy if you want to cast shadows from very simple objects and don't want / can't use shadowmaps or have unity pro. Keep in mind that this might be efficient for objects with a small number of polys; if your receiving object is flat and you want to optimize you might want to use a projection matrix instead. Hope this help and comes useful.

Take care,

Eugenio

 

Am I able to order the rendering (queue?)? I'm asking since if I only could render the shadows before the terrain, I could render the shadows in an opaque gray and then blend in the terrain. Any thought appreciated. Thanks,

Eugenio

 

Thanks Eugenio,

I appreciate you sharing that. I'm not going to use it for anything "as is", but I'm very interested in learning Unity's communication between scripts and shaders. This is a good example of using the mesh interface in conjunction with a shader. I'm very interested in learning how a process like Shadow Volume Extrusion can be implented in Unity with this combo.

Thanks for sharing this,
Ethan