How to set Matrix as a Property?

Matrices aren't supported by the Properties block, so they aren't supported in the Material inspector. You can still use Get/SetMatrix() to fill out float4x4 uniforms in your Cg blocks, or any matrices you use as parameters to fixed function commands. As this example code shows, you don't need a definition in Properties to be able to call SetMatrix(): manual for Material.SetMatrix()

 

That could be the problem. I haven't tried to use a matrix in a surface shader yet. Just to be sure, though, you're doing something like this?

Code (csharp):

1.  
2. ...
3.  
4. public class ObjectBlur : MonoBehaviour {
5.     ...
6.     protected void LateUpdate() {
7.         Vector4 currentPosition = transform.position;
8.         currentPosition.w = 1f;
9.         // Calculate ModelView matrices
10.         Matrix4x4 _mv = CameraInfo.ViewMatrix*transform.localToWorldMatrix;
11.         Matrix4x4 _mvPrev = CameraInfo.PrevViewMatrix*m_prevModelMatrix;
12.         // Give material the matrices it needs
13. [COLOR="red"]       m_stretchMaterial.SetMatrix("_mv", _mv);
14.         m_stretchMaterial.SetMatrix("_mvPrev", _mvPrev);
15.         m_stretchMaterial.SetMatrix("_mvInvTrans", _mv.transpose.inverse);
16.         m_stretchMaterial.SetMatrix("_mvpPrev", CameraInfo.PrevViewProjMatrix*m_prevModelMatrix);[/COLOR]
17.         // Record our previous transform
18.         m_prevModelMatrix = transform.localToWorldMatrix;
19.     }
20.    
21.     ...
22. }

And in the shader:

Code (csharp):

1. Shader "Hidden/Motion Vectors" {
2.     SubShader {
3.         Tags { "RenderType"="Moving" }
4.         Pass {
5.             Fog { Mode Off }
6.             CGPROGRAM
7.                 #pragma vertex vert
8.                 #pragma fragment frag
9.                 #pragma fragmentoption ARB_fog_exp2
10.                 #pragma fragmentoption ARB_precision_hint_fastest
11.                 #include "UnityCG.cginc"
12.                
13.                 ...
14.                
15. [COLOR="red"]               uniform float4x4 _mv;
16.                 uniform float4x4 _mvPrev;
17.                 uniform float4x4 _mvInvTrans;
18.                 uniform float4x4 _mvpPrev;[/COLOR]
19.                
20.                 ...
21.             ENDCG
22.         }
23.     }
24.     ...
25. }

 

Perhaps a quick explanation of the relationship between Materials and Shaders might help:

Materials are basically a reference to a shader, and a dictionary of property names to values. When you set a Material to use a specific shader, it will immediately add keys to its dictionary for all the exposed properties in the shader. It won't look at the content of the shader beyond the Properties block, though, so it won't contain values for matrices by default.

If you're just using GetMatrix(), there won't be anything stored for you to get. If you set a matrix first, though, then it should be added to the dictionary and work for retrieval later.

 

Mostly messing about and reading everything I can. I figured out that particular relationship by looking at Materials using the debug mode of the inspector. There you can see that Materials don't actually ever forget their keys. This is useful when you switch from one shader to another, where both share a set of property names. It's a little weird, though, because if you switch between two completely different shaders, all your property values will be saved. This means that if you switch shaders a lot, a Material will accumulate an arbitrary number of property names and values in its dictionary. In practice, though, the benefits of Materials always remembering things outweigh the potential for a (hilarious) memory leak.