From ec23aa58095978df40540702a750496172bb32b3 Mon Sep 17 00:00:00 2001
From: Supakorn 'Jamie' Rassameemasmuang <jamievlin@outlook.com>
Date: Thu, 29 Feb 2024 00:59:16 -0700
Subject: [PATCH] GLSL: Use linear color for blending pixels in transparent
 rendering.

---
 base/shaders/blend.glsl    | 18 ++++++++++++++++++
 base/shaders/fragment.glsl | 11 +++++++----
 2 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/base/shaders/blend.glsl b/base/shaders/blend.glsl
index e3ff9ecb7..288b37f8b 100644
--- a/base/shaders/blend.glsl
+++ b/base/shaders/blend.glsl
@@ -58,6 +58,21 @@ vec4 blend(vec4 outColor, vec4 color)
   return mix(outColor,color,color.a);
 }
 
+const float gamma=2.2;
+const float invGamma=1.0/gamma;
+
+/**
+ * @brief Converts linear color (measuring photon count) to srgb (what our brain thinks
+ * is the brightness
+ * example linearToPerceptual(vec3(0.5)) is approximately vec3(0.729)
+ */
+vec3 linearToPerceptual(vec3 inColor)
+{
+  // an actual 0.5 brightness (half amount of photons) would
+  // look brighter than what our eyes think is "half" light
+  return pow(inColor, vec3(invGamma));
+}
+
 void main()
 {
   uint pixel=uint(gl_FragCoord.y)*push.constants[1]+uint(gl_FragCoord.x);
@@ -159,5 +174,8 @@ void main()
     }
   }
 
+  vec3 perceptualColor=linearToPerceptual(outColor.rgb);
+  outColor = vec4(perceptualColor, outColor.a);
+
   COUNT(pixel)=0u;
 }
diff --git a/base/shaders/fragment.glsl b/base/shaders/fragment.glsl
index 7ff28b588..d8a2eabda 100644
--- a/base/shaders/fragment.glsl
+++ b/base/shaders/fragment.glsl
@@ -287,15 +287,18 @@ void main() {
   // (e.g. our 0.5 is much much brighter than what swap chain/monitor thinks 0.5 is)
   // need to give the output image the color our brain perceives with the same photon count
   // as the original pixel
-  vec3 outColorInPerceptualSpace=linearToPerceptual(outColor.rgb);
-  outColor=vec4(outColorInPerceptualSpace,outColor.a);
+  vec4 linearColor=outColor;
+
+  // outColor is our output vector, so save what we have as linear color
+  vec3 outColorInPerceptualSpace=linearToPerceptual(linearColor.rgb);
+  outColor=vec4(outColorInPerceptualSpace,linearColor.a);
 
 #ifndef WIDTH // TODO DO NOT DO THE DEPTH COMPARISON WHEN NO TRANSPARENT OBJECTS!
   uint pixel=uint(gl_FragCoord.y)*push.constants[1]+uint(gl_FragCoord.x);
 #if defined(TRANSPARENT) || (!defined(HAVE_INTERLOCK) && !defined(OPAQUE))
   uint element=INDEX(pixel);
   uint listIndex=atomicAdd(offset[element],-1u)-1u;
-  fragment[listIndex]=outColor;
+  fragment[listIndex]=linearColor;
   depth[listIndex]=gl_FragCoord.z;
 #ifndef WIREFRAME
   discard;
@@ -306,7 +309,7 @@ void main() {
   if(opaqueDepth[pixel] == 0.0 || gl_FragCoord.z < opaqueDepth[pixel])
     {
     opaqueDepth[pixel]=gl_FragCoord.z;
-    opaqueColor[pixel]=outColor;
+    opaqueColor[pixel]=linearColor;
   }
   endInvocationInterlockARB();
 #endif