[Bf-blender-cvs] [d2cc672b0c1] master: Fix soft light blend mode math

[Richard Antalik]

Commit: d2cc672b0c12287b4602e1c26fd9d75010df9558
Author: Richard Antalik
Date:   Tue Jan 4 01:54:35 2022 +0100
Branches: master
https://developer.blender.org/rBd2cc672b0c12287b4602e1c26fd9d75010df9558

Fix soft light blend mode math

Function `blend_color_softlight_float` used math different to compositor and
produced result that had abrupt value changes.

Use math based on modified screen blend mode as compositor does.

===================================================================

M	source/blender/blenlib/intern/math_color_blend_inline.c

===================================================================

diff --git a/source/blender/blenlib/intern/math_color_blend_inline.c b/source/blender/blenlib/intern/math_color_blend_inline.c
index a19537bca0f..73ecb2cf798 100644
--- a/source/blender/blenlib/intern/math_color_blend_inline.c
+++ b/source/blender/blenlib/intern/math_color_blend_inline.c
@@ -896,15 +896,9 @@ MINLINE void blend_color_softlight_float(float dst[4], const float src1[4], cons
     int i = 3;
 
     while (i--) {
-      float temp;
-
-      if (src1[i] < 0.5f) {
-        temp = (src2[i] + 0.5f) * src1[i];
-      }
-      else {
-        temp = 1.0f - ((1.0f - (src2[i] + 0.5f)) * (1.0f - src1[i]));
-      }
-      dst[i] = (temp * fac + src1[i] * mfac);
+      float screen = 1.0f - (1.0f - src1[i]) * (1.0f - src2[i]);
+      float soft_light = ((1.0f - src1[i]) * src2[i] + screen) * src1[i];
+      dst[i] = src1[i] * mfac + soft_light * fac;
     }
   }
   else {