Selectively darken bright parts of Rendertexture?

Hi, I'm super noob when it comes to shaders... hoping for some help on what is hopefully a simple problem to fix... I'm using ARFoundation and getting the phone's camera image to blit to a rendertexture to make reflection probes. Some of the shaders that rely on the reflection probe get messed up/washed out if the colors are too bright or too white.

Here is the shader code that creates the skybox from the Rendertexture:

Code (CSharp):

1. Shader "AR/ARSkybox"
2. {
3.     Properties
4.     {
5.         _LightingTex("Render Texture", 2D) = "black" {}
6.     }
7.  
8.     CGINCLUDE
9.  
10.     #include "UnityCG.cginc"
11.  
12.     struct appdata
13.     {
14.         float4 position : POSITION;
15.         float3 normal : NORMAL;
16.         float3 texcoord : TEXCOORD0;
17.     };
18.  
19.     struct v2f
20.     {
21.         float4 position : SV_POSITION;
22.         float2 texcoord : TEXCOORD0;
23.     };
24.  
25.     // This relies on a RenderTexture of this name being created in ARCoreCameraRenderTexture.cs.
26.     sampler2D _LightingTex;
27.     float4x4 _WorldToCameraMatrix;
28.  
29.     float2 SphereMapUVCoords( float3 viewDir, float3 normal )
30.     {
31.         // Sphere mapping. Find reflection and tranform into UV coords.
32.         // Heavily inspired by https://www.clicktorelease.com/blog/creating-spherical-environment-mapping-shader/
33.         float3 reflection = reflect(-viewDir, normal);
34.         float m = 2. * sqrt(
35.             pow(reflection.x, 2.) +
36.             pow(reflection.y, 2.) +
37.             pow(reflection.z + 1., 2.)
38.         );
39.         return reflection.xy / m + .5;
40.     }
41.  
42.     v2f vert(appdata v)
43.     {
44.         // Create a sphere map with a texture whose center is at the viewDir/sphere intersection.
45.         // The texture is wrapped around the sphere so that the corners meet directly behind the camera.
46.         // To do this we could operate in static viewDir (0,0,1) space. We always want to look at the center on the texture.
47.         // When we move the phone, there is no need to change the view direction.
48.         // When rendering a skybox, the view direction is altered for each face. Grab the world space view direction to each vert
49.         //  then reverse the camera's view direction, bringing it back to view space.
50.         float3 viewDir = -normalize(WorldSpaceViewDir(v.position));
51.         viewDir = mul(_WorldToCameraMatrix, float4(viewDir,0));
52.  
53.         v2f o;
54.         o.position = UnityObjectToClipPos(v.position);
55.         o.texcoord = SphereMapUVCoords(viewDir, v.normal);
56.  
57.         return o;
58.     }
59.  
60.     fixed4 frag(v2f i) : COLOR
61.     {
62.         return tex2D(_LightingTex, i.texcoord);
63.     }
64.  
65.     ENDCG
66.  
67.     SubShader
68.     {
69.         Tags{ "RenderType" = "Background" "Queue" = "Background" }
70.             Pass
71.         {
72.             ZWrite Off
73.             Cull Off
74.             Fog{ Mode Off }
75.             CGPROGRAM
76. #pragma fragmentoption ARB_precision_hint_fastest
77. #pragma vertex vert
78. #pragma fragment frag
79.             ENDCG
80.         }
81.     }
82. }

I'm wondering if there is a way to selectively darken the brighter areas of the rendertexture input, hopefully without killing performance on mobile... Perhaps limiting RGB values to less then 200??? I'm hoping there's an easy/cheap way to do this in the "fixed4 frag(v2f i) : COLOR" section...

 

In the frag, instead of instantly returning the result of tex2D(), store the result:

fixed4 col = tex2D(_LightingTex, i.texcoord);

Now you can do whatever simple math on the R,G,B components of

col

, and then

return col;

.

You wouldn't really want to limit the individual values to 200 though, because that will cause color shift. It would be better to do some scaling based on the combined r+g+b value.

 

Thanks so much for the pointers! I think I got it figured out!