Merge pull request #19621 from WestLangley/dev_aces

Shaders: Improve ACES Filmic tone mapping

src/renderers/shaders/ShaderChunk/tonemapping_pars_fragment.glsl.js

@@ -31,11 +31,42 @@ vec3 OptimizedCineonToneMapping( vec3 color ) {
 
 }
 
-// source: https://knarkowicz.wordpress.com/2016/01/06/aces-filmic-tone-mapping-curve/
+// source: https://github.com/selfshadow/ltc_code/blob/master/webgl/shaders/ltc/ltc_blit.fs
+vec3 RRTAndODTFit( vec3 v ) {
+
+    vec3 a = v * ( v + 0.0245786 ) - 0.000090537;
+    vec3 b = v * ( 0.983729 * v + 0.4329510 ) + 0.238081;
+    return a / b;
+
+}
+
 vec3 ACESFilmicToneMapping( vec3 color ) {
 
-	color *= toneMappingExposure;
-	return saturate( ( color * ( 2.51 * color + 0.03 ) ) / ( color * ( 2.43 * color + 0.59 ) + 0.14 ) );
+    // sRGB => XYZ => D65_2_D60 => AP1 => RRT_SAT
+    const mat3 ACESInputMat = mat3(
+        vec3( 0.59719, 0.07600, 0.02840 ), // transposed from source
+        vec3( 0.35458, 0.90834, 0.13383 ),
+        vec3( 0.04823, 0.01566, 0.83777 )
+    );
+
+    // ODT_SAT => XYZ => D60_2_D65 => sRGB
+    const mat3 ACESOutputMat = mat3(
+        vec3(  1.60475, -0.10208, -0.00327 ), // transposed from source
+        vec3( -0.53108,  1.10813, -0.07276 ),
+        vec3( -0.07367, -0.00605,  1.07602 )
+    );
+
+    color *= toneMappingExposure;
+
+    color = ACESInputMat * color;
+
+    // Apply RRT and ODT
+    color = RRTAndODTFit( color );
+
+    color = ACESOutputMat * color;
+
+    // Clamp to [0, 1]
+    return saturate( color );
 
 }
 `;