How does one Render a texture directly to the Camera in Unity

Question

In Unity, I have 2 images in the form of a texture that I am merging together (one overlaying the other). I do this in a Compute Shader and put the results on a RenderTexture. I want this RenderTexture to be everything that the output camera sees.

I have found articles saying to use a the ReplacementShader property of the camera, but I couldn't get that to properly work.

Currently I have simply put the RenderTexture onto a UIRawImage that covers the whole UI Canvas so that the entire camera is filled. This however has a lot of lag and is obviously a suboptimal solution.

So how does one output the Rendertexture or the compute Shader result directly onto the camera. Thanks.

Answer 1

You could probably use OnRenderImage

Event function that Unity calls after a Camera has finished rendering, that allows you to modify the Camera's final image.

and use Graphics.Blit

Copies source texture into destination render texture with a shader.

and do something like e.g.

// This script goes onto your according Camera
public class RenderReplacement : MonoBehaviour
{
    public RenderTexture replacement;

    void OnRenderImage(RenderTexture src, RenderTexture dest)
    {
        // To overwrite the entire screen
        Graphics.Blit(replacement, null);

        // Or to overwrite only what this specific Camera renders
        //Graphics.Blit(replacement, dest);
    }
}

Where

dest
The destination RenderTexture. Set this to null to blit directly to screen. See description for more information.

---

Note as mentioned in the API the OnRenderImage is called after this Camera already finished rendering. So in order to make this more efficient - since we basically throw away that render - simply make sure that camera basically isn't rendering anything by disabling all Layers and e.g. let it only render a single color background