4 files changed, 95 insertions, 8 deletions

diff --git a/include/painter/color.h b/include/painter/color.h
new file mode 100644
index 0000000..2aeee3e
--- /dev/null
+++ b/include/painter/color.h
@@ -0,0 +1,61 @@
+#ifndef UPEM_MORPHING_COLOR
+#define UPEM_MORPHING_COLOR
+
+/**
+ * File: color.h
+ *
+ * See also:
+ *   A rainbow
+ */
+
+#include <MLV/MLV_color.h>
+#include <stdbool.h>
+#include "common/time.h"
+
+/**
+ * Type: ColorComponent
+ * Represents a single colour component of 32-bits RGBa tuple.
+ */
+typedef uint8_t ColorComponent;
+
+/**
+ * Type: ColorPixel
+ * Represents a single RGBa coloured pixel.
+ * Compatible with the libMLV representation.
+ */
+typedef union {
+  struct {
+    ColorComponent a, b, g, r;
+  } rgba;
+
+  MLV_Color mlv;
+} Color;
+
+/**
+ * Function: color_equals
+ * Compares the supplied colors.
+ *
+ * Parameters:
+ *   c1 - the first color
+ *   c2 - the second color
+ *
+ * Returns:
+ *   T(c1 is the same color as c2)
+ */
+bool color_equals(Color c1, Color c2);
+
+/**
+ * Function: color_blend
+ * Blends two colors.
+ *
+ * Parameters:
+ *   origin   - the first color
+ *   target   - the second color
+ *   distance - the distance from the first color
+ *
+ * Returns:
+ *   The blended color
+ */
+Color color_blend(Color origin, Color target, TimeVector distance);
+
+#endif
diff --git a/src/blender/color.c b/src/blender/color.c
deleted file mode 100644
index f92fba9..0000000
--- a/src/blender/color.c
+++ /dev/null
@@ -1,8 +0,0 @@
-#include "blender/color.h"
-
-bool color_equals(Color c1, Color c2) {
-  return c1.rgba.r == c2.rgba.r &&
-         c1.rgba.g == c2.rgba.g &&
-         c1.rgba.b == c2.rgba.b &&
-         c1.rgba.a == c2.rgba.a;
-}
diff --git a/src/painter/color.c b/src/painter/color.c
new file mode 100644
index 0000000..65c4f20
--- /dev/null
+++ b/src/painter/color.c
@@ -0,0 +1,20 @@
+#include "painter/color.h"
+#include <math.h>
+
+static inline ColorComponent blend_component(ColorComponent origin, ColorComponent target, TimeVector frame) {
+  return (ColorComponent) round(sqrt((TIME_UNIT - frame) * pow(origin, 2) + frame * pow(target, 2)));
+}
+
+bool color_equals(Color c1, Color c2) {
+  return c1.rgba.r == c2.rgba.r &&
+         c1.rgba.g == c2.rgba.g &&
+         c1.rgba.b == c2.rgba.b &&
+         c1.rgba.a == c2.rgba.a;
+}
+
+Color color_blend(Color origin, Color target, TimeVector distance) {
+  return (Color) {{blend_component(origin.rgba.a, target.rgba.a, distance),
+                   blend_component(origin.rgba.b, target.rgba.b, distance),
+                   blend_component(origin.rgba.g, target.rgba.g, distance),
+                   blend_component(origin.rgba.r, target.rgba.r, distance)}};
+}
diff --git a/test/painter/color.c b/test/painter/color.c
new file mode 100644
index 0000000..bdfe9b3
--- /dev/null
+++ b/test/painter/color.c
@@ -0,0 +1,14 @@
+#include "painter/color.h"
+#include <assert.h>
+
+static void test_color_blend() {
+  Color a = {{1, 10, 100, 200}}, b = {{100, 1, 200, 10}};
+  assert(color_equals(color_blend(a, b, TIME_ORIGIN), a));
+  assert(color_equals(color_blend(a, b, TIME_UNIT), b));
+  assert(color_equals(color_blend(a, b, 0.25), (Color) {{50, 9, 132, 173}}));
+}
+
+int main(int argc, char **argv) {
+  test_color_blend();
+  return 0;
+}