Apply the sRGB OETF in the shader instead of the LUT

filament/src/materials/colorGrading/colorGrading.fs

@@ -1,13 +1,27 @@
+vec3 oetfSRGB(vec3 x) {
+    float a  = 0.055f;
+    float a1 = 1.055f;
+    float b  = 12.92f;
+    float p  = 1.0f / 2.4f;
+    for (int i = 0; i < 3; i++) {
+        x[i] = x[i] <= 0.0031308f ? x[i] * b : a1 * pow(x[i], p) - a;
+    }
+    return x;
+}
+
 vec3 colorGrade(mediump sampler3D lut, const vec3 x) {
     // Alexa LogC EI 1000
-    const float a = 5.555556;
-    const float b = 0.047996;
-    const float c = 0.244161 / log2(10.0);
-    const float d = 0.386036;
-    vec3 logc = c * log2(a * x + b) + d;
+    // const float a = 5.555556;
+    // const float b = 0.047996;
+    // const float c = 0.244161 / log2(10.0);
+    // const float d = 0.386036;
+    // vec3 logc = c * log2(a * x + b) + d;
 
     // Remap to sample pixel centers
-    logc = materialParams.lutSize.x + logc * materialParams.lutSize.y;
+    // logc = materialParams.lutSize.x + logc * materialParams.lutSize.y;
 
-    return textureLod(lut, logc, 0.0).rgb;
+    // return textureLod(lut, logc, 0.0).rgb;
+
+    // Testing: apply the sRGB OETF in the shader.
+    return oetfSRGB(x);
 }