Multiple Render Target (MRT) questions

There's little documentation and examples about this subject and i can't seem to find what i'm looking for, which got me thinking after a few tries that maybe what i thought about MRT is all wrong

I want to be able to render my scene to a target and some other information to another target in just one pass

1. Is it possible?
2. Should i use RenderWithShader with a second camera or SetReplacementShader with my main camera?
3. Is the replacement shader the one responsible to render the two colors outputs?
4. Do i need to use a GL.Quad to use MRT?

I'm extremely confused about this subject, i was able to create a secondary camera and use renderwithshader with a shader that would render the color in one target and the alpha in another but the draw calls exploded, 2 draw calls per object to be precise, if i just use setreplacementshader in the main camera i get nothing and if i use a GL.Quad without replacement shaders i can renders colors to it but not my scene using this example: http://forum.unity3d.com/threads/mrt-example.152050/#post-1118431

Could anyone point some directions? I thought the whole purpose in using MRT was to save draw calls by rendering various information at the same time to later use them for screen effects

 

I use MRTs in my code. I just draw a quad and use a specialised output structure.

https://github.com/brianasu/unitygi/blob/master/Assets/simple voxelisation/Scripts/LightBleeding.cs

private void RenderMRT(RenderBuffer[] renderBuffers, RenderBuffer depthBuffer)
{

Graphics.SetRenderTarget(renderBuffers, depthBuffer);
GL.Clear(false, true, Color.clear);
GL.PushMatrix();
GL.LoadOrtho();
VoxelMaterial.SetPass(6);
GL.Begin(GL.QUADS);
GL.TexCoord2(0.0f, 0.0f); GL.Vertex3(0.0f, 0.0f, 0.1f);
GL.TexCoord2(1.0f, 0.0f); GL.Vertex3(1.0f, 0.0f, 0.1f);
GL.TexCoord2(1.0f, 1.0f); GL.Vertex3(1.0f, 1.0f, 0.1f);
GL.TexCoord2(0.0f, 1.0f); GL.Vertex3(0.0f, 1.0f, 0.1f);
GL.End();
GL.PopMatrix();​

}

Then i have a fragment shader

https://github.com/brianasu/unitygi/blob/master/Assets/simple voxelisation/Shader/Voxelize.shader

struct COL_OUTPUT
{

float4 albedo : COLOR0;
float4 depthNormals : COLOR1;​

};


COL_OUTPUT fragDownsampleRSM(v2f IN)
{

COL_OUTPUT o;
.....
return o;​

}

 

I tried the quad method, i couldn't get it to render my scene in a different target... say you want render the scene as is in a target and some other information that comes from the object in another, can i do that with the quad method? i'll definitely try it out, also i notice you are running the code in LateUpdate, i wasn't expecting that, do you have additional draw calls for doing like this?

 

Sorry didn't read your post carefully. I did a quick test and it seems to work. I think the problem might be is that it doesn't seem to work with deferred rendering. You have to switch it to forward rendering. I'm not sure why but I haven't looked yet. I've copy pasted my test code. Hope this helps

Test Code

Code (CSharp):

1. using UnityEngine;
2. using System.Collections;
3.  
4. public class TestMRT : MonoBehaviour {
5.  
6.     public Shader mrtShader;
7.  
8.     Camera ppCamera;
9.     RenderTexture texA;
10.     RenderTexture texB;
11.  
12.     void OnEnable()
13.     {
14.         texA = RenderTexture.GetTemporary(Screen.width, Screen.height, 16, RenderTextureFormat.ARGB32);
15.         texB = RenderTexture.GetTemporary(Screen.width, Screen.height, 16, RenderTextureFormat.ARGB32);
16.     }
17.  
18.     void OnDisable()
19.     {
20.         RenderTexture.ReleaseTemporary(texA);
21.         RenderTexture.ReleaseTemporary(texB);
22.     }
23.    
24.     void Update()
25.     {
26.         if(ppCamera == null)
27.         {
28.             var go = new GameObject("PP Camera", typeof(Camera));
29.             ppCamera = go.camera;
30.  
31.             ppCamera.enabled = false;
32.  
33.         }
34.         ppCamera.CopyFrom(camera);
35.         ppCamera.clearFlags = CameraClearFlags.SolidColor;
36.         ppCamera.backgroundColor = Color.black;
37.  
38.         ppCamera.SetTargetBuffers(new RenderBuffer [] { texA.colorBuffer, texB.colorBuffer }, texA.depthBuffer);
39.         ppCamera.RenderWithShader(mrtShader, "RenderType");
40.     }
41.  
42.     void OnGUI()
43.     {
44.         GUI.DrawTexture(new Rect(0, 0, 256, 256), texA);
45.         GUI.DrawTexture(new Rect(256, 0, 256, 256), texB);
46.     }
47. }

My Shader

Code (CSharp):

1. Shader "Hidden/Test MRT" {
2.  
3. CGINCLUDE
4. #include "UnityCG.cginc"
5. #include "TerrainEngine.cginc"
6.  
7. struct v2f {
8.     float4 pos : POSITION;
9. };
10.  
11. struct COL_OUTPUT
12. {
13.     float4 albedoA : COLOR0;
14.     float4 albedoB : COLOR1;
15. };
16.  
17. v2f vert( appdata_base v ) {
18.     v2f o;
19.     o.pos = mul(UNITY_MATRIX_MVP, v.vertex);  
20.     return o;
21. }
22.  
23. COL_OUTPUT fragMRT(v2f i)
24. {
25.     COL_OUTPUT o;
26.     o.albedoA = float4(1, 0, 0, 1);
27.     o.albedoB = float4(0, 1, 0, 1);
28.     return o;
29. }
30.  
31. ENDCG
32.  
33. Subshader
34. {
35.     Tags {"RenderType"="Opaque"}
36.     Pass {
37.         Fog { Mode Off }
38.  
39.         CGPROGRAM
40.         #pragma vertex vert
41.         #pragma fragment fragMRT
42.         ENDCG
43.     }
44. }
45.  
46. Fallback Off
47. }