Resurrect previous version of the linear light formula and fix it

app/operations/layer-modes/gimpoperationlayermode.c

@@ -1782,7 +1782,14 @@ blendfun_linear_light (const float *dest,
           for (c = 0; c < 3; c++)
             {
               gfloat comp;
-              comp = dest[c] + 2.0f * src[c] - 1.0f;
+              if (src[c] <= 0.5f)
+                {
+                  comp = dest[c] + 2.0 * src[c] - 1.0f;
+                }
+              else
+                {
+                  comp = dest[c] + 2.0 * (src[c] - 0.5f);
+                }
               out[c] = comp;
             }
         }
@@ -1964,117 +1971,94 @@ static GimpLayerModeInfo gimp_layer_mode_infos[]=
   { GIMP_LAYER_MODE_NORMAL,
     "gimp:normal",
     0,
-    GIMP_LAYER_COMPOSITE_SRC_OVER,
   },
   { GIMP_LAYER_MODE_DISSOLVE,
     "gimp:dissolve",
     GIMP_LAYER_MODE_FLAG_WANTS_LINEAR_DATA,
-    GIMP_LAYER_COMPOSITE_SRC_OVER,
   },
   { GIMP_LAYER_MODE_BEHIND,
     "gimp:behind",
     0,
-    GIMP_LAYER_COMPOSITE_DST_ATOP,
   },
   { GIMP_LAYER_MODE_MULTIPLY_LEGACY,
     "gimp:multiply-legacy",
-    GIMP_LAYER_MODE_FLAG_LEGACY,
+    GIMP_LAYER_MODE_FLAG_LEGACY
-    GIMP_LAYER_COMPOSITE_SRC_ATOP,
   },
   { GIMP_LAYER_MODE_SCREEN_LEGACY,
     "gimp:screen-legacy",
     GIMP_LAYER_MODE_FLAG_LEGACY,
-    GIMP_LAYER_COMPOSITE_SRC_ATOP,
   },
   { GIMP_LAYER_MODE_OVERLAY_LEGACY,
     "gimp:overlay-legacy",
     GIMP_LAYER_MODE_FLAG_LEGACY,
-    GIMP_LAYER_COMPOSITE_SRC_ATOP,
   },
   { GIMP_LAYER_MODE_DIFFERENCE_LEGACY,
     "gimp:difference-legacy",
     GIMP_LAYER_MODE_FLAG_LEGACY,
-    GIMP_LAYER_COMPOSITE_SRC_ATOP,
   },
   { GIMP_LAYER_MODE_ADDITION_LEGACY,
     "gimp:addition-legacy",
     GIMP_LAYER_MODE_FLAG_LEGACY,
-    GIMP_LAYER_COMPOSITE_SRC_ATOP,
   },
   { GIMP_LAYER_MODE_SUBTRACT_LEGACY,
     "gimp:subtract-legacy",
     GIMP_LAYER_MODE_FLAG_LEGACY,
-    GIMP_LAYER_COMPOSITE_SRC_ATOP,
   },
   { GIMP_LAYER_MODE_DARKEN_ONLY_LEGACY,
     "gimp:darken-only-legacy",
     GIMP_LAYER_MODE_FLAG_LEGACY,
-    GIMP_LAYER_COMPOSITE_SRC_ATOP,
   },
   { GIMP_LAYER_MODE_LIGHTEN_ONLY_LEGACY,
     "gimp:lighten-only-legacy",
     GIMP_LAYER_MODE_FLAG_LEGACY,
-    GIMP_LAYER_COMPOSITE_SRC_ATOP,
   },
   { GIMP_LAYER_MODE_HSV_HUE_LEGACY,
     "gimp:hsv-hue-legacy",
     GIMP_LAYER_MODE_FLAG_LEGACY,
-    GIMP_LAYER_COMPOSITE_SRC_ATOP,
   },
   { GIMP_LAYER_MODE_HSV_SATURATION_LEGACY,
     "gimp:hsv-saturation-legacy",
     GIMP_LAYER_MODE_FLAG_LEGACY,
-    GIMP_LAYER_COMPOSITE_SRC_ATOP,
   },
   { GIMP_LAYER_MODE_HSV_COLOR_LEGACY,
     "gimp:hsv-color-legacy",
     GIMP_LAYER_MODE_FLAG_LEGACY,
-    GIMP_LAYER_COMPOSITE_SRC_ATOP,
   },
   { GIMP_LAYER_MODE_HSV_VALUE_LEGACY,
     "gimp:hsv-value-legacy",
     GIMP_LAYER_MODE_FLAG_LEGACY,
-    GIMP_LAYER_COMPOSITE_SRC_ATOP,
   },
   { GIMP_LAYER_MODE_DIVIDE_LEGACY,
     "gimp:divide-legacy",
     GIMP_LAYER_MODE_FLAG_LEGACY,
-    GIMP_LAYER_COMPOSITE_SRC_ATOP,
   },
   { GIMP_LAYER_MODE_DODGE_LEGACY,
     "gimp:dodge-legacy",
     GIMP_LAYER_MODE_FLAG_LEGACY,
-    GIMP_LAYER_COMPOSITE_SRC_ATOP,
   },
   { GIMP_LAYER_MODE_BURN_LEGACY,
     "gimp:burn-legacy",
     GIMP_LAYER_MODE_FLAG_LEGACY,
-    GIMP_LAYER_COMPOSITE_SRC_ATOP,
   },
   { GIMP_LAYER_MODE_HARDLIGHT_LEGACY,
     "gimp:hardlight-legacy",
     GIMP_LAYER_MODE_FLAG_LEGACY,
-    GIMP_LAYER_COMPOSITE_SRC_ATOP,
   },
   { GIMP_LAYER_MODE_SOFTLIGHT_LEGACY,
     "gimp:softlight-legacy",
     GIMP_LAYER_MODE_FLAG_LEGACY,
-    GIMP_LAYER_COMPOSITE_SRC_ATOP,
   },
   { GIMP_LAYER_MODE_GRAIN_EXTRACT_LEGACY,
     "gimp:grain-extract-legacy",
     GIMP_LAYER_MODE_FLAG_LEGACY,
-    GIMP_LAYER_COMPOSITE_SRC_ATOP,
   },
   { GIMP_LAYER_MODE_GRAIN_MERGE_LEGACY,
     "gimp:grain-merge-legacy",
     GIMP_LAYER_MODE_FLAG_LEGACY,
-    GIMP_LAYER_COMPOSITE_SRC_ATOP,
   },
   { GIMP_LAYER_MODE_COLOR_ERASE,
     "gimp:color-erase",
     0,
-    GIMP_LAYER_COMPOSITE_SRC_ATOP,
   },
   { GIMP_LAYER_MODE_OVERLAY,
     "gimp:layer-mode",