Fix T70605: incorrect darken and lighten rgb mix mode

Differential Revision: https://developer.blender.org/D6058

Reviewers: brecht, fclem

intern/cycles/kernel/shaders/node_mix.osl

@@ -91,12 +91,12 @@ color node_mix_diff(float t, color col1, color col2)
 
 color node_mix_dark(float t, color col1, color col2)
 {
-  return min(col1, col2) * t + col1 * (1.0 - t);
+  return mix(col1, min(col1, col2), t);
 }
 
 color node_mix_light(float t, color col1, color col2)
 {
-  return max(col1, col2 * t);
+  return mix(col1, max(col1, col2), t);
 }
 
 color node_mix_dodge(float t, color col1, color col2)

intern/cycles/kernel/svm/svm_color_util.h

@@ -92,12 +92,12 @@ ccl_device float3 svm_mix_diff(float t, float3 col1, float3 col2)
 
 ccl_device float3 svm_mix_dark(float t, float3 col1, float3 col2)
 {
-  return min(col1, col2) * t + col1 * (1.0f - t);
+  return interp(col1, min(col1, col2), t);
 }
 
 ccl_device float3 svm_mix_light(float t, float3 col1, float3 col2)
 {
-  return max(col1, col2 * t);
+  return interp(col1, max(col1, col2), t);
 }
 
 ccl_device float3 svm_mix_dodge(float t, float3 col1, float3 col2)

source/blender/gpu/shaders/material/gpu_shader_material_mix_rgb.glsl

@@ -92,14 +92,14 @@ void mix_diff(float fac, vec4 col1, vec4 col2, out vec4 outcol)
 void mix_dark(float fac, vec4 col1, vec4 col2, out vec4 outcol)
 {
   fac = clamp(fac, 0.0, 1.0);
-  outcol.rgb = min(col1.rgb, col2.rgb * fac);
+  outcol.rgb = mix(col1.rgb, min(col1.rgb, col2.rgb), fac);
   outcol.a = col1.a;
 }
 
 void mix_light(float fac, vec4 col1, vec4 col2, out vec4 outcol)
 {
   fac = clamp(fac, 0.0, 1.0);
-  outcol.rgb = max(col1.rgb, col2.rgb * fac);
+  outcol.rgb = mix(col1.rgb, max(col1.rgb, col2.rgb), fac);
   outcol.a = col1.a;
 }