Damage full-screen red color with burn blend effect?

I'm looking to add a full-screen red damage effect to my game when the first-person player gets hit, and currently I'm using a simple UI element that adjusts it's opacity depending on the amount of damage, but it's a solid, linear color effect and I'm hoping to make it so the luminance is affected, similar to a photoshop effect. So for instance, instead of:



Something more like (darken):

Or (overlay):


I presume this could be done with a shader, but I'm not sure how. I'm also not sure if this could (or should!) be done as a shader on a UI element, or if it would be a fullscreen blit efffect (I'm using built-in render pipeline, so I can't really use any special pipeline tricks).

 

Can be easily done with a shader. The default shader created when you ask for a image effect shader (Create->Shader->Image Effect Shader) will invert the entire screen's colors:

Code (CSharp):

1. fixed4 frag (v2f i) : SV_Target
2.             {
3.                 fixed4 col = tex2D(_MainTex, i.uv);
4.                 // just invert the colors
5.                 col.rgb = 1 - col.rgb;
6.                 return col;
7.             }

so instead of inverting colors, multiply them with red:

Code (CSharp):

1.  
2. fixed4 frag (v2f i) : SV_Target
3.             {
4.                 fixed4 col = tex2D(_MainTex, i.uv);
5.                 // tint red:
6.                 col.rgb *= half3(1,0,0);
7.                 return col;
8.             }

To apply the shader, use the OnRenderImage callback and call Graphics.Blit inside of it.
https://docs.unity3d.com/550/Documentation/Manual/WritingImageEffects.html

 

Thankyou! If I'm already using graphics blit for another effect (such as underwater distortion) would this add to an existing graphics blit or override it?

 

It entirely depends on what you want it to look like. I'd assume you need the red tinting to happen after underwater distortion, so probably you want to add a new Graphics.Blit() at the end that takes the distorted image as input and outputs a red-tinted distorted image .