Run a shader once on a texture

Questions & Answers
1

I’ve found/made a gaussian blur shader which works perfectly, but the game runs a lot slower than without it. Since I want to use it for depth of field in 2d, it could just be applied once when the level starts. I’ve heard about Graphics.Blit but I have no idea how that works.
I basically want to change the sprite to a blurred version of itself (via this blur shader I found for example). How can I do this?

2

I would recommend pre-processing the textures outside of the game for a number of reasons - not only is it easier, but it also means many objects can reuse the same textures rather than creating new textures for every instance. If you really need to do this, then yes you can use Graphics.Blit to render into a RenderTexture then read that back to a Texture2D;

[SerializeField] private Shader m_Shader;

private Material m_Material;

public Texture2D BlurTexture (Texture2D a_SourceTex)
{
    //Make sure we have a material
    if (m_Material == null)
        m_Material = new Material (m_Shader);

    //Get a temporary RenderTexture and draw our source texture into it using our shader
    RenderTexture tmp = RenderTexture.GetTemporary (a_SourceTex.width, a_SourceTex.height, 0);
    Graphics.Blit (a_Source, tmp, m_Material);

    //Store the last active RT and set our new one as active
    RenderTexture lastActive = RenderTexture.active;
    RenderTexture.active = tmp;

    //Read the blurred texture into a new Texture2D
    Texture2D blurTex = new Texture2D (tmp.width, tmp.height);
    blurTex.ReadPixels (new Rect (0, 0, tmp.width, tmp.height), 0, 0);
    blurTex.Apply ();

    //Restore the last active RT and release our temp tex
    RenderTexture.active = lastActive;
    RenderTexture.ReleaseTemporary (tmp);

    return blurTex;
}

Something along those lines. Note that this is meant for image effect/unlit shaders - things like surface shaders will probably turn out weird if they even work at all.