Add HsvToRgb routine (backported from eed9a67)

Author: cahirwpz

include/color.h

@@ -8,4 +8,6 @@ extern u_char colortab[4096];
 /* Each argument must be in range 0-15. */
 u_short ColorTransition(u_short from, u_short to, u_short step);
 
+u_short HsvToRgb(short h, short s, short v);
+
 #endif

lib/libgfx/HsvToRgb.c

@@ -0,0 +1,58 @@
+#include <color.h>
+
+/* Based on https://stackoverflow.com/a/14733008 */
+u_short HsvToRgb(short h, short s, short v) {
+  short region, remainder, p, q, t;
+  u_char r, g, b;
+
+  if (s == 0) {
+    v &= 0xf0;
+    return (v << 4) | v | (v >> 4);
+  }
+
+  region = h / 43;
+  remainder = (h - (region * 43)) * 6;
+
+  p = (v * (short)(255 - s)) >> 8;
+  q = (v * (short)(255 - ((s * remainder) >> 8))) >> 8;
+  t = (v * (short)(255 - ((s * (short)(255 - remainder)) >> 8))) >> 8;
+
+  switch (region) {
+    case 0:
+      r = v;
+      g = t;
+      b = p;
+      break;
+    case 1:
+      r = q;
+      g = v;
+      b = p;
+      break;
+    case 2:
+      r = p;
+      g = v;
+      b = t;
+      break;
+    case 3:
+      r = p;
+      g = q;
+      b = v;
+      break;
+    case 4:
+      r = t;
+      g = p;
+      b = v;
+      break;
+    default:
+      r = v;
+      g = p;
+      b = q;
+      break;
+  }
+
+  r &= 0xf0;
+  g &= 0xf0;
+  b &= 0xf0;
+
+  return (r << 4) | g | (b >> 4);
+}

lib/libgfx/Makefile

@@ -26,6 +26,7 @@ SOURCES := \
 	DeleteCopList.c \
 	DeletePixmap.c \
 	EndSprite.c \
+	HsvToRgb.c \
 	InitSharedBitmap.c \
 	InsideArea.c \
 	LoadPalette.c \