Invert the colors of the Camera

Hi,
I've been dealing with this problem for many days.

I want to invert the colors of all my scene in my Android Game.
I tried using post-processing efects, but I didn't see any of them that could invert the colors.

I also tried to use shaders, although I don't know much about them.
I applied a shader to the Camera (I copied and pasted the code of Unity Standard Assets -> Image Effects, I founded a shader that inverts colors and I pasted there).
Now in the editor and in some android devices (those who have a lot of cpu and gpu) works like a charm.

The problem is that in low-quality android devices it all starts doing strange things and the game seems almost blocked when I active that shader.

How should I do? I don't know much about shaders.
Thanks

 

The default image effect shader that Unity creates when you create a new image effect shader in the project view is actually a color inversion shader. It's a super simple effect.

The problem with old android devices is the way Unity handles image effects is to copy the frame buffer to a render texture and pass that to the image effect shader. This is pretty fast on most hardware, but very very slow on older hardware. The usual fix people will suggest is to not use Unity's built in OnRenderImage and instead have your camera render directly to a render texture and do everything with command buffers and manually swapping the render target.

However for the effect of flipping the color there's an easy way that doesn't require using image effects, or render textures, or any of this. All that's needed is a quad in front of the camera with a very simple shader.

Code (CSharp):

1. Shader "Custom/InvertColor"
2. {
3.     SubShader
4.     {
5.         Pass
6.         {
7.             Tags { "Queue"="Overlay+100" "IgnoreProjector"="True" }
8.  
9.             Blend OneMinusDstColor Zero
10.             ColorMask RGB
11.  
12.             ZWrite Off
13.             ZTest Always
14.  
15.             CGPROGRAM
16.             #pragma vertex vert
17.             #pragma fragment frag
18.  
19.             float4 vert(float4 vertex : POSITION) : SV_Position {
20.               return UnityObjectToClipPos(vertex);
21.             }
22.  
23.             fixed4 frag() : SV_Target {
24.               return fixed4(1,1,1,1);
25.             }
26.  
27.             ENDCG
28.         }
29.     }
30. }

The key part is that Blend line. Basically the rest of the shader does the absolute minimum work possible to render the mesh to the screen, and the blend mode is what tells it to render the current screen color inverted.

edit: Fixed shader so it compiles

 

Hi,

Thanks for your answer, the shader you did works perfectly.
I did what you said, a quad with your shader. I tried it in low-quality mobiles and it works! Thank you very much!

I have a last question, I need to change the colour from normal to inverted in a transition, like if normal was 0 and inverted color was 1, what I would do is change the value from 0 to 0.25, then 0.5, etc.


Thank you so much, this was the last thing I needed to finish my game.

 

bgolus' shader can't change the inversion level, but this can be fixed:

Code (CSharp):

1.     Shader "Custom/InvertColor"
2.     Properties {
3.         _TintColor ("Tint Color", Color) = (1,1,1,1)
4.     }
5.     {
6.         SubShader
7.         {
8.             Pass
9.             {
10.                 Tags { "Queue"="Overlay+100" "IgnoreProjector"="True" }
11.    
12.                 Blend OneMinusDstColor OneMinusSrcColor
13.                 ColorMask RGB
14.    
15.                 ZWrite Off
16.                 ZTest Always
17.    
18.                 CGPROGRAM
19.                 #pragma vertex vert
20.                 #pragma fragment frag
21.    
22.                 float4 vert(float4 vertex : POSITION) : SV_Position {
23.                   return UnityObjectToClipPos(vertex);
24.                 }
25.    
26.                 fixed4 frag() : SV_Target {
27.                   return fixed4(1,1,1,1);
28.                 }
29.    
30.                 ENDCG
31.             }
32.         }
33.     }

Then you change the Tint Color between black and white (or other color like red for actually tinting the result). In script you SetColor to _TintColor and apply lerp to RGB (alpha is irrelevant).

 

It works fine, like bgolus's one.
But when I try to set the colour like you said, nothing changes.

Code (CSharp):

1. material.SetColor("_TintColor", Color.Lerp(Color.white, Color.black, 1f));
2. //and then the same but from  black to white
3. material.SetColor("_TintColor", Color.Lerp(Color.black, Color.white, 1f));

If I change the color manually in the inspector, nothing changes either.
The texture is black and remains black.

I think I should learn how to code shaders
Thanks for everything!

 

I believe @ifurkend forgot to update the shader fully. He defined the _TintColor property and modified the Blend mode, but never actually makes use of the new property. I suspect this is what he had intended to post.

Code (CSharp):

1. Shader "Custom/InvertColor"
2. {
3.     Properties {
4.         _TintColor ("Tint Color", Color) = (1,1,1,1)
5.     }
6.     SubShader
7.     {
8.         Pass
9.         {
10.             Tags { "Queue"="Overlay+100" "IgnoreProjector"="True" }
11.    
12.             Blend OneMinusDstColor OneMinusSrcColor
13.             ColorMask RGB
14.    
15.             ZWrite Off
16.             ZTest Always
17.  
18.             CGPROGRAM
19.             #pragma vertex vert
20.             #pragma fragment frag
21.    
22.             float4 vert(float4 vertex : POSITION) : SV_Position {
23.               return UnityObjectToClipPos(vertex);
24.             }
25.  
26.             fixed4 _TintColor;
27.  
28.             fixed4 frag() : SV_Target {
29.               return _TintColor;
30.             }
31.  
32.             ENDCG
33.         }
34.     }
35. }

 

Thank you very much for your help!!
Now the shader works perfectly, and in low-quality mobiles it does too!

I can finally end my game.
Many thanks to both for your help!!

 

@bgolus: Yes. Because I already have my invert color shader, I forgot to compile the code before posting... orz

 

I realize this thread is a couple of years old, but is there a way to "cut a hole" in the inverted shader above using a texture with transparency?

Here's what I've got:

Code (CSharp):

1. Shader "Custom/InvertColor1"
2. {
3.     Properties{
4.         _TintColor("Tint Color", Color) = (1,1,1,1)
5.         //_MainTex("Base (RGB)", 2D) = "white" {} TODO
6.     }
7.         SubShader
8.     {
9.         Pass
10.         {
11.             Tags { "Queue" = "Overlay+100" "IgnoreProjector" = "True" }
12.  
13.             Blend OneMinusDstColor OneMinusSrcColor
14.             ColorMask RGB
15.  
16.             ZWrite Off
17.             ZTest Always
18.  
19.             CGPROGRAM
20.             #pragma vertex vert
21.             #pragma fragment frag
22.  
23.             float4 vert(float4 vertex : POSITION) : SV_Position {
24.               return UnityObjectToClipPos(vertex);
25.             }
26.  
27.             fixed4 _TintColor;
28.  
29.             fixed4 frag() : SV_Target {
30.               return _TintColor;
31.             }
32.  
33.             ENDCG
34.         }
35.     }
36. }