From d208c16c438e91e3f12af711b2348e69a54f63f3 Mon Sep 17 00:00:00 2001
From: Tavian Barnes <tavianator@gmail.com>
Date: Wed, 13 Jan 2010 20:03:09 -0500
Subject: New use dmnsn_color_gradient() for weighted reflections.

---
 libdimension/color.c           | 44 ++++++++++++++++++------------------------
 libdimension/dimension/color.h |  2 +-
 libdimension/reflective.c      |  8 +-------
 3 files changed, 21 insertions(+), 33 deletions(-)

diff --git a/libdimension/color.c b/libdimension/color.c
index 5220dfa..9e1ef4f 100644
--- a/libdimension/color.c
+++ b/libdimension/color.c
@@ -323,31 +323,6 @@ dmnsn_color_add(dmnsn_color c1, dmnsn_color c2)
   return ret;
 }
 
-/* Subtract two colors */
-dmnsn_color
-dmnsn_color_sub(dmnsn_color c1, dmnsn_color c2)
-{
-  dmnsn_sRGB sRGB1 = dmnsn_sRGB_from_color(c1);
-  dmnsn_sRGB sRGB2 = dmnsn_sRGB_from_color(c2);
-
-  dmnsn_sRGB sRGB = {
-    .R = sRGB1.R - sRGB2.R,
-    .G = sRGB1.G - sRGB2.G,
-    .B = sRGB1.B - sRGB2.B
-  };
-
-  dmnsn_color ret = dmnsn_color_from_sRGB(sRGB);
-
-  /* Weighted average of transparencies by intensity */
-  dmnsn_CIE_Lab Lab1 = dmnsn_Lab_from_color(ret, dmnsn_whitepoint);
-  dmnsn_CIE_Lab Lab2 = dmnsn_Lab_from_color(ret, dmnsn_whitepoint);
-  if (Lab1.L + Lab2.L) {
-    ret.filter = (Lab1.L*c1.filter - Lab2.L*c2.filter)/(Lab1.L + Lab2.L);
-    ret.trans  = (Lab1.L*c1.trans  - Lab2.L*c2.trans )/(Lab1.L + Lab2.L);
-  }
-  return ret;
-}
-
 /* Multiply a color by a scalar */
 dmnsn_color
 dmnsn_color_mul(double n, dmnsn_color color)
@@ -363,6 +338,25 @@ dmnsn_color_mul(double n, dmnsn_color color)
   return ret;
 }
 
+/* For n in [0, 1] get the color in a gradient between c1 and c2 */
+dmnsn_color
+dmnsn_color_gradient(dmnsn_color c1, dmnsn_color c2, double n)
+{
+  dmnsn_sRGB sRGB1 = dmnsn_sRGB_from_color(c1);
+  dmnsn_sRGB sRGB2 = dmnsn_sRGB_from_color(c2);
+
+  dmnsn_sRGB sRGB = {
+    .R = n*(sRGB2.R - sRGB1.R) + sRGB1.R,
+    .G = n*(sRGB2.G - sRGB1.G) + sRGB1.G,
+    .B = n*(sRGB2.B - sRGB1.B) + sRGB1.B
+  };
+
+  dmnsn_color ret = dmnsn_color_from_sRGB(sRGB);
+  ret.filter = n*(c2.filter - c1.filter) + c1.filter;
+  ret.trans  = n*(c2.trans  - c1.trans)  + c1.trans;
+  return ret;
+}
+
 /* Filters `color' through `filter' */
 dmnsn_color
 dmnsn_color_filter(dmnsn_color color, dmnsn_color filter)
diff --git a/libdimension/dimension/color.h b/libdimension/dimension/color.h
index 43edbff..9627ce8 100644
--- a/libdimension/dimension/color.h
+++ b/libdimension/dimension/color.h
@@ -88,8 +88,8 @@ dmnsn_sRGB    dmnsn_sRGB_from_color(dmnsn_color color);
 
 /* Perceptual color manipulation */
 dmnsn_color dmnsn_color_add(dmnsn_color color1, dmnsn_color color2);
-dmnsn_color dmnsn_color_sub(dmnsn_color color1, dmnsn_color color2);
 dmnsn_color dmnsn_color_mul(double n, dmnsn_color color);
+dmnsn_color dmnsn_color_gradient(dmnsn_color c1, dmnsn_color c2, double n);
 dmnsn_color dmnsn_color_filter(dmnsn_color color, dmnsn_color filter);
 dmnsn_color dmnsn_color_illuminate(dmnsn_color light, dmnsn_color color);
 double dmnsn_color_difference(dmnsn_color color1, dmnsn_color color2);
diff --git a/libdimension/reflective.c b/libdimension/reflective.c
index f1c7355..f44e4ff 100644
--- a/libdimension/reflective.c
+++ b/libdimension/reflective.c
@@ -40,13 +40,7 @@ dmnsn_reflective_finish_fn(const dmnsn_finish *finish,
   double reflection = pow(dmnsn_vector_dot(ray, normal), params->falloff);
 
   return dmnsn_color_illuminate(
-    dmnsn_color_add(
-      dmnsn_color_mul(
-        reflection,
-        dmnsn_color_sub(params->max, params->min)
-      ),
-      params->min
-    ),
+    dmnsn_color_gradient(params->min, params->max, reflection),
     reflect
   );
 }
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