sys/color: added RGB inversion and complementary color

sys/color/color.c

@@ -15,6 +15,7 @@
  *
  * @author      Hauke Petersen <hauke.petersen@fu-berlin.de>
  * @author      Cenk Gündoğan <mail@cgundogan.de>
+ * @author      Simon Brummer <brummer.simon@googlemail.com>
  *
  * @}
  */
@@ -175,3 +176,20 @@ void color_rgb2str(const color_rgb_t *rgb, char* str)
     tmp = rgb->b & 0x0F;
     str[5] = (tmp > 9) ? ('A' - 10 + tmp) : ('0' + tmp);
 }
+
+void color_rgb_complementary(const color_rgb_t *rgb, color_rgb_t *comp_rgb)
+{
+    uint8_t  max = 0;
+    uint8_t  min = 0;
+    uint16_t val = 0;
+
+    max = (rgb->r > rgb->g) ? rgb->r : rgb->g;
+    max = (rgb->b > max) ? rgb->b : max;
+    min = (rgb->r < rgb->g) ? rgb->r : rgb->g;
+    min = (rgb->b < min) ? rgb->b : min;
+    val = max + min;
+
+    comp_rgb->r = val - rgb->r;
+    comp_rgb->g = val - rgb->g;
+    comp_rgb->b = val - rgb->b;
+}

sys/include/color.h

@@ -17,6 +17,7 @@
  *
  * @author      Hauke Petersen <hauke.petersen@fu-berlin.de>
  * @author      Cenk Gündoğan <mail@cgundogan.de>
+ * @author      Simon Brummer <brummer.simon@googlemail.com>
  */
 
 #ifndef __COLOR_H
@@ -104,6 +105,34 @@ void color_str2rgb(const char *str, color_rgb_t *color);
  */
 void color_rgb2str(const color_rgb_t *rgb, char *str);
 
+/**
+ * @brief Invert a given rgb color
+ *
+ * @pre                 ((rgb != NULL) && (inv_rgb != NULL))
+ *
+ * @param[in] rgb       Input rgb color, that should be converted. Must be NOT NULL
+ * @param[out] inv_rgb  Output rgb color, result of the conversion. Must be NOT NULL
+ */
+static inline void color_rgb_invert(const color_rgb_t *rgb, color_rgb_t *inv_rgb)
+{
+    inv_rgb->r = rgb->r ^ 0xFF;
+    inv_rgb->g = rgb->g ^ 0xFF;
+    inv_rgb->b = rgb->b ^ 0xFF;
+}
+
+/**
+ * @brief Calculate the complementary color of a given rgb color.
+ *
+ * @note                Complementary color calculation according to adobe illustator calculations.
+ *                      See https://helpx.adobe.com/illustrator/using/adjusting-colors.html
+ *
+ * @pre                 ((rgb != NULL) && (comp_rgb != NULL))
+ *
+ * @param[in] rgb       Input rgb color. Must be NOT NULL
+ * @param[out] comp_rgb Output rgb color, result of the complementary color calculation. Must be NOT NULL
+ */
+void color_rgb_complementary(const color_rgb_t *rgb, color_rgb_t *comp_rgb);
+
 #ifdef __cplusplus
 }
 #endif

tests/unittests/tests-color/tests-color.c

@@ -73,6 +73,34 @@ static void test_rgb2hex__success(void)
     TEST_ASSERT_EQUAL_INT(0x000AB13C, hex);
 }
 
+static void test_rgb_invert__success(void)
+{
+    const color_rgb_t col = {.r = 100, .g = 128, .b =   0};
+    const color_rgb_t res = {.r = 155, .g = 127, .b = 255};
+    color_rgb_t tmp;
+
+    color_rgb_invert(&col, &tmp);
+
+    TEST_ASSERT_EQUAL_INT(res.r, tmp.r);
+    TEST_ASSERT_EQUAL_INT(res.g, tmp.g);
+    TEST_ASSERT_EQUAL_INT(res.b, tmp.b);
+}
+
+
+static void test_rgb_complementary__success(void)
+{
+    /* See example: https://helpx.adobe.com/illustrator/using/adjusting-colors.html */
+    const color_rgb_t col = {.r = 102, .g = 153, .b =  51};
+    const color_rgb_t res = {.r = 102, .g =  51, .b = 153};
+    color_rgb_t tmp;
+
+    color_rgb_complementary(&col, &tmp);
+
+    TEST_ASSERT_EQUAL_INT(res.r, tmp.r);
+    TEST_ASSERT_EQUAL_INT(res.g, tmp.g);
+    TEST_ASSERT_EQUAL_INT(res.b, tmp.b);
+}
+
 Test *tests_color_tests(void)
 {
     EMB_UNIT_TESTFIXTURES(fixtures) {
@@ -81,6 +109,8 @@ Test *tests_color_tests(void)
         new_TestFixture(test_hex2rgb__success),
         new_TestFixture(test_rgb2hex__success),
         new_TestFixture(test_rgb2str__success),
+        new_TestFixture(test_rgb_invert__success),
+        new_TestFixture(test_rgb_complementary__success),
     };
 
     EMB_UNIT_TESTCALLER(color_tests, NULL, NULL, fixtures);