Introduce Khronos Neutral tonemapper as new default along with debug options to control tonemap mix (#2464) (#2468)

indra/newview/app_settings/settings.xml

@@ -9832,6 +9832,28 @@
         <key>Value</key>
         <real>0.4</real>
     </map>
+    <key>RenderTonemapMix</key>
+    <map>
+        <key>Comment</key>
+        <string>Mix between linear and tonemapped colors (0.0(Linear) - 1.0(Tonemapped)</string>
+        <key>Persist</key>
+        <integer>1</integer>
+        <key>Type</key>
+        <string>F32</string>
+        <key>Value</key>
+        <real>1.0</real>
+    </map>
+    <key>RenderTonemapType</key>
+    <map>
+        <key>Comment</key>
+        <string>What tonemapper to use: 0 = Khronos Neutral, 1 = ACES</string>
+        <key>Persist</key>
+        <integer>1</integer>
+        <key>Type</key>
+        <string>U32</string>
+        <key>Value</key>
+        <integer>0</integer>
+    </map>
     <key>ReplaySession</key>
     <map>
       <key>Comment</key>

indra/newview/app_settings/shaders/class1/deferred/postDeferredGammaCorrect.glsl

@@ -29,9 +29,7 @@ out vec4 frag_color;
 
 uniform sampler2D diffuseRect;
 
-uniform float exposure;
 uniform float gamma;
-uniform float aces_mix;
 uniform vec2 screen_res;
 in vec2 vary_fragcoord;
 

indra/newview/app_settings/shaders/class1/deferred/postDeferredTonemap.glsl

@@ -95,9 +95,33 @@ vec3 toneMapACES_Hill(vec3 color)
     return color;
 }
 
+// Khronos Neutral tonemapping
+// https://github.com/KhronosGroup/ToneMapping/tree/main
+// Input color is non-negative and resides in the Linear Rec. 709 color space.
+// Output color is also Linear Rec. 709, but in the [0, 1] range.
+vec3 PBRNeutralToneMapping( vec3 color )
+{
+  const float startCompression = 0.8 - 0.04;
+  const float desaturation = 0.15;
+
+  float x = min(color.r, min(color.g, color.b));
+  float offset = x < 0.08 ? x - 6.25 * x * x : 0.04;
+  color -= offset;
+
+  float peak = max(color.r, max(color.g, color.b));
+  if (peak < startCompression) return color;
+
+  const float d = 1. - startCompression;
+  float newPeak = 1. - d * d / (peak + d - startCompression);
+  color *= newPeak / peak;
+
+  float g = 1. - 1. / (desaturation * (peak - newPeak) + 1.);
+  return mix(color, newPeak * vec3(1, 1, 1), g);
+}
+
 uniform float exposure;
-uniform float gamma;
-uniform float aces_mix;
+uniform float tonemap_mix;
+uniform int tonemap_type;
 
 vec3 toneMap(vec3 color)
 {
@@ -106,8 +130,20 @@ vec3 toneMap(vec3 color)
 
     color *= exposure * exp_scale;
 
-    // mix ACES and Linear here as a compromise to avoid over-darkening legacy content
-    color = mix(toneMapACES_Hill(color), color, aces_mix);
+    vec3 clamped_color = clamp(color.rgb, vec3(0.0), vec3(1.0));
+
+    switch(tonemap_type)
+    {
+    case 0:
+        color = PBRNeutralToneMapping(color);
+        break;
+    case 1:
+        color = toneMapACES_Hill(color);
+        break;
+    }
+
+    // mix tonemapped and linear here to provide adjustment
+    color = mix(clamped_color, color, tonemap_mix);
 #endif
 
     return color;
@@ -125,14 +161,6 @@ void debugExposure(inout vec3 color)
     }
 }
 
-vec3 legacyGamma(vec3 color)
-{
-    vec3 c = 1. - clamp(color, vec3(0.), vec3(1.));
-    c = 1. - pow(c, vec3(gamma)); // s/b inverted already CPU-side
-
-    return c;
-}
-
 void main()
 {
     //this is the one of the rare spots where diffuseRect contains linear color values (not sRGB)

indra/newview/pipeline.cpp

@@ -7087,10 +7087,16 @@ void LLPipeline::tonemap(LLRenderTarget* src, LLRenderTarget* dst)
         F32 e = llclamp(exposure(), 0.5f, 4.f);
 
         static LLStaticHashedString s_exposure("exposure");
-        static LLStaticHashedString aces_mix("aces_mix");
+        static LLStaticHashedString tonemap_mix("tonemap_mix");
+        static LLStaticHashedString tonemap_type("tonemap_type");
 
         shader.uniform1f(s_exposure, e);
-        shader.uniform1f(aces_mix, gEXRImage.notNull() ? 0.f : 0.3f);
+
+        static LLCachedControl<U32> tonemap_type_setting(gSavedSettings, "RenderTonemapType", 0U);
+        shader.uniform1i(tonemap_type, tonemap_type_setting);
+
+        static LLCachedControl<F32> tonemap_mix_setting(gSavedSettings, "RenderTonemapMix", 1.f);
+        shader.uniform1f(tonemap_mix, tonemap_mix_setting);
 
         mScreenTriangleVB->setBuffer();
         mScreenTriangleVB->drawArrays(LLRender::TRIANGLES, 0, 3);