Shaders not working in Graphics.Blit when using my own RenderTexture

Unity Engine
1

Hey Guys,

I am currently working on a system that allows users to edit and paint on to multiple custom built texture layers that will then be blended together to a render texture and applied to a material. The current issue that I am having is a problem with the Graphics.Blit() function.

When I pass in my source texture and my own RenderTexture and include a material containing a shader (any shader, even “Diffuse”) my output is black as if nothing was copied to the RenderTexture.

Graphics.Blit(src, dest, ms_TextureBlendMaterial); //<-- output is black.

If I use the same parameters but set the destination RenderTexture to null, then everything works and the output is displayed to the screen RECT.

Graphics.Blit(src, null, ms_TextureBlendMaterial); //<-- correct output but is of course rendered to the screen Rect.

If I use my own RenderTexture but remove the material parameter so that I am simply copying my source texture to the RenderTexture that also works.

Graphics.Blit(src, dest); //<-- works

I looked at compositor effects as a reference as they basically achieve what I am trying to do. I have seen that many examples first link the RenderTexture to a camera and then call Blit() within the OnRenderImage() call. Must the RenderTexture be linked to a camera when attemping to pass a shader through the blit function? I’m sure I am making some stupid little mistake or missing some concept here but any information would be appreciated.

This is a snippet of my TextureModification class:

public class TextureManipulation
{
    static bool ms_bLoaded = false;
    static Material ms_TextureBlendMaterial;

    static void Init()
    {
        if (ms_bLoaded)
            return;

        ms_TextureBlendMaterial = new Material(Shader.Find("LayerBlend"));
        ms_bLoaded = true;
    }

    //This gets called every frame 
    public static void BlendTextures(Texture src, Texture blendTex, ref RenderTexture dest)
    {
        Init();
        ms_TextureBlendMaterial.SetTexture("_BlendTex", blendTex);
        Graphics.Blit(src, dest, ms_TextureBlendMaterial);
        RenderTexture.active = null;
    }

    ...
}

Cheers.

Merge vert-frag and surf shader for drawing system
2

I’m fighting the same problem, seems to have been around for some time (http://answers.unity3d.com/questions/35482/graphicsblit-using-a-material-does-not-work.html).

I’m trying to understand why it seems to work in several ImageEffects (like Grayscaleeffect). One difference is probably that most image effects render directly to screen or render to a GL generated quad, but still it would be nice to understand why Graphics.blit do not work when the target is a RenderTexture.

Update (solved): Now looking at the shader used in Grayscaleeffect I can see that it is a fragment shader, not a surface shader. I have tried not to get into CG-programming in my current project, but it seems that all the shaders now use CGPROGRAM, and the Grayscaleeffect is only a few lines of code. I managed to edit the shader to perform exactly what I was trying to do.
Now using a material with my newly created /modified fragment shader, the Graphics.Blit(src,dst,mm) works perfectly !

So there seems to be a requirement that the shader used in Graphics.Blit() has to be a fragment shader. (need to read more about this now that it seems to work), would have been nice to have a comment on that on the documentation pages :wink:

3

Thank you. That was the exact same issue that was happening to me. I was using a CGPROGRAM but it was using a surface shader. Once I modified it to use a fragment shader instead, the output to my custom RenderTexture was valid.

I was very much hoping that my issue was some silly little thing like this rather than having to re-think my entire approach. I do agree, having this minor detail included in the documentation for Graphics.Blit() would have been be nice.

Cheers

4

Thanks very much, guys. The hint with the Greyscale Effect helped me fix my problem, which was very similar to 0xDEADCODE’s. My blit with my custom material/shader returned black. My shader was already a fragment shader, but I forgot one more thing:

ZTest Always Cull Off ZWrite Off
Fog { Mode off }

Adding these lines (within Pass{}) made mine work (mostly because of the ZTest Always; I guess the ZTest just failed for every pixel earlier). Hope I can help some other people with the same issue.

2 Likes
5

Thank you! Thank you! Thank you! Now, my homework for tonight is figure out what these lines of code mean… and why this would have fixed anything.
I was having a problem where my shader (already a fragment shader) worked in the first scene but would not work in a subsequent scene that used the same shader. My shader didn’t even return black it just returned something like a blur even though it was a pixelate shader.

6

this issue is mainly caused by dds format textures, make sure to find and replace them with jpeg or any other supported formats on IOS.