CustomRenderTexture initialization in same update cancels out shader?

I'm trying to use a CustomRenderTexture to achieve an image effects. I have a very simple CustomRenderTexture in my assets folder which has initialization set to texture and set to update in Realtime. Then I have my effect material with my update shader and my named update pass which is also set to update in Realtime.

What I expect is that at the beginning of every frame the initializer will go first, filling the CustomRenderTexture with the texture and THEN my image effect material/shader will update but it appears that in ANY frame where the initializer executes then the shader material will not be updated/rendered in that frame. So the result is that every frame I'm just seeing the plain, unmodified texture.

Here is my image effect shader:

Code (CSharp):

1. Shader "CustomRenderTexture/MultiplyRed"
2. {
3.     Properties
4.     {
5.                                 _Tex("InputTex", 2D) = "white" {}
6.      }
7.  
8.      SubShader
9.      {
10.         Lighting Off
11.         Blend One Zero
12.  
13.         Pass
14.         {
15.             CGPROGRAM
16.             #include "UnityCustomRenderTexture.cginc"
17.             #pragma vertex CustomRenderTextureVertexShader
18.             #pragma fragment frag
19.              #pragma target 3.0
20.  
21.  
22.                                         sampler2D   _Tex;
23.  
24.             float4 frag(v2f_customrendertexture IN) : COLOR
25.             {
26.                 return float4(1,0,0,1) * tex2D(_SelfTexture2D, IN.localTexcoord.xy);
27.             }
28.             ENDCG
29.                     }
30.     }
31. }

Note that I do have "Double Buffered" enabled, so I am confused as to why this isn't working! Any advice? Why would you ever want the initializer in Realtime if it means that it can never be updated?

 

Could maybe a Unity developer explain this behavior?

 

@Julien_Unity Thank you for this explanation. So if I want to use a single non-double buffered update how do I sample the initialization result texture in the update material shader? Before I was trying to use _SelfTexture2D and double-buffer because I couldn't figure out how to sample the initalization result texture from the documentation and I assumed that the initialized texture would be in the buffer in the first update but that was not true.

 

@Julien_Unity What I'm actually trying to do is get around a limitation I hit with using CommandBuffers for a screen-space image effect. What I was doing required a buffer (via Blit to a temporary RenderTexture) because I need to capture the screen contents, blit to a temporary RenderTexture using the image effect shader, then use the results of that image effect shader as an input for another pass.

Unfortunately I need the timing of the screen capture to happen right before the render queue position of the mesh my shader is applied to but Camera.AddCommandBuffer() needs a CameraEvent and CameraEvents are not synchronized with the shader render queue nor is there enough granularity (I need to render between 3000-3500 in the shader queue but CameraEvent only gives me BeforeForwardAlpha and AfterForwardAlpha)

So afterall I guess what I need out of CustomRenderTextures was the chaining behavior of being able to chain one into another. My idea was to put a GrabPass in the first CRT, do the first update pass, and hand the result to the next CRT, effectively giving me GrabPass AND a frame buffer. But now that I think about it the timing of the GrabPass won't work out unless the evaluation of the CRT chain STARTS when a material uses the final CRT's output as an input texture or if it happens before any meshes are rendered.

 

Followed your advice of just putting the GrabPass in the update shader of my CustomRenderTexture update material. Unfortunately this too crashes Unity.

 

That might be my only option though. How would I go about doing this?

 

I see where you're going but actually now that I think about it that wouldn't solve my problem because of the same reason I tried CRT in the first place: CommandBuffer execution timing doesn't have enough granularity for what I'm trying to do. :/

I think the only thing that might help is Scriptable Render Loop but that's a ways off and until then I can't release my Asset on the store. :/