Kandinsky: Introduce KDColorRGB

Change-Id: Ic64f2ff9a441580940d37151e190fd0a3d954d8a

kandinsky/Makefile

@@ -8,7 +8,10 @@ objs += $(addprefix kandinsky/src/,\
   text.o\
   types.o\
 )
-tests += $(addprefix kandinsky/test/, set_pixel.c)
+tests += $(addprefix kandinsky/test/,\
+  color.c\
+  set_pixel.c\
+)
 
 FREETYPE_PATH := /usr/local/Cellar/freetype/2.6.3
 # LIBPNG_PATH is optional. If LIBPNG_PATH is not defined, rasterizer will be

kandinsky/include/kandinsky/color.h

@@ -3,8 +3,21 @@
 
 #include <stdint.h>
 
+// Kandinsky uses RGB565
+
 typedef uint16_t KDColor;
 
-#define KDColorRGB(r,g,b) ((KDColor)(((r&0x1F)<<11)&((g&0x3F)<<5)&(b&0x1F)))
+/* KDColorRGB takes a 32-bits RGB color and builds a KDColor from it.
+ * Given KDColor is RGB565 and that we take 8-bit values for R, G, and B,
+ * some shifting has to happen. */
+
+#define KDColorRGB(r,g,b) ((KDColor)((((((uint16_t)(r))>>3)&0x1F)<<11)|(((((uint16_t)(g))>>2)&0x3F)<<5)|((((uint16_t)(b))>>3)&0x1F)))
+
+#define KDColorBlack KDColorRGB(0x00, 0x00, 0x00)
+#define KDColorWhite KDColorRGB(0xFF, 0xFF, 0xFF)
+
+#define KDColorRed KDColorRGB(0xFF, 0x00, 0x00)
+#define KDColorGreen KDColorRGB(0x00, 0xFF, 0x00)
+#define KDColorBlue KDColorRGB(0x00, 0x00, 0xFF)
 
 #endif

kandinsky/test/color.c

@@ -0,0 +1,18 @@
+#include <quiz.h>
+#include <kandinsky.h>
+#include <assert.h>
+
+QUIZ_CASE(kandinsky_color_rgb) {
+  KDColor foo = KDColorRGB(0xFF, 0, 0);
+  assert(KDColorRGB(0xFF, 0, 0) == 0xF800);
+  assert(KDColorRGB(0, 0xFF, 0) == 0x07E0);
+  assert(KDColorRGB(0, 0, 0xFF) == 0x1F);
+  /* R = 0x12 = 0b 0001 0010. 5 most important bits are 00010.
+   * G = 0x34 = 0b 0011 0100. 6 most important bits are 001101.
+   * B = 0x56 = 0b 0101 0110. 5 most important bits are 01010.
+   * KDColor = 0b 00010 001101 01010
+   *         = 0b 0001 0001 1010 1010
+   *         = 0x    1    1 A    A */
+  assert(KDColorRGB(0x12, 0x34, 0x56) == 0x11AA);
+}
+