feat(color): add color module

README.md

@@ -9,6 +9,7 @@ functions can be found in the header files (with a short description) as well
 as in the source files (with a detailed description and explanation of
 parameters and return values).
 
+- `color`: Color conversion and manipulation functions
 - `common`: Common utilities that are very common but did not fit in any other
   module, e.g. safe memory allocation or a few math functions
 - `cstr`: Functions that expand C's `<string.h>` library for `char *` strings

lib/color.c

@@ -0,0 +1,155 @@
+#include "color.h"
+#include <errno.h>
+#include <math.h>
+
+/**
+ * turn a floating point rgb struct (r, g, b, a in [0.0f .. 1.0f]) into an
+ * integer rgb struct (r, g, b, a in [0 .. 255]).
+ *
+ * @param   rgbf: the rgbf_t struct to convert
+ *
+ * @return  the corresponding rgb_t struct
+ */
+rgb_t
+rgbf_to_rgb (rgbf_t rgbf)
+{
+    return (rgb_t) {
+        .r = (u8) lroundf (rgbf.r * 255.0f),
+        .g = (u8) lroundf (rgbf.g * 255.0f),
+        .b = (u8) lroundf (rgbf.b * 255.0f),
+        .a = (u8) lroundf (rgbf.a * 255.0f),
+    };
+}
+
+/**
+ * turn an integer rgb struct (r, g, b, a in [0 .. 255]) into a floating point
+ * rgb struct (r, g, b, a in [0.0f .. 1.0f]).
+ *
+ * @param   rgb: the rgb_t struct to convert
+ *
+ * @return  the corresponding rgbf_t struct
+ */
+rgbf_t
+rgb_to_rgbf (rgb_t rgb)
+{
+    return (rgbf_t) {
+        .r = ((f32) rgb.r) / 255.0f,
+        .g = ((f32) rgb.g) / 255.0f,
+        .b = ((f32) rgb.b) / 255.0f,
+        .a = ((f32) rgb.a) / 255.0f,
+    };
+}
+
+/**
+ * get the corresponding rgb color (integer) to a given hsl color. on error,
+ * errno is set and a zero-initialized struct is returned.
+ *
+ * @param   hsl: the hsl color
+ *
+ * @return  the corresponding rgb color
+ *
+ * @errno   EINVAL: invalid hsl value passed
+ */
+inline rgb_t
+hsl_to_rgb (hsl_t hsl)
+{
+    return rgbf_to_rgb (hsl_to_rgbf (hsl));
+}
+
+/**
+ * get the corresponding rgb color (floating point) to a given hsl color. on
+ * error, errno is set and a zero-initialized struct is returned.
+ *
+ * @param   hsl: the hsl color
+ *
+ * @return  the corresponding rgb color
+ *
+ * @errno   EINVAL: invalid hsl value passed
+ *
+ * @see     https://en.wikipedia.org/wiki/HSL_and_HSV#Color_conversion_formulae
+ */
+rgbf_t
+hsl_to_rgbf (hsl_t hsl)
+{
+    f32 c, h2, m, x;
+    rgbf_t rgbf;
+
+    if (hsl.h > 360 || hsl.s < 0.0f || hsl.s > 1.0f ||
+        hsl.l < 0.0f || hsl.s > 1.0f)
+        return errno = EINVAL, (rgbf_t) {0};
+
+    c = (1.0f - fabsf (2.0f * hsl.l - 1.0f)) * hsl.s;
+    h2 = ((f32) hsl.h) / 60.0f;
+    x = c * (1.0f - fabsf (fmodf (h2, 2.0f) - 1.0f));
+    m = hsl.l - (c / 2.0f);
+    x += m;
+    c += m;
+
+    if      (h2 <  1.0f) { rgbf.r = c; rgbf.g = x; rgbf.b = m; }
+    else if (h2 <  2.0f) { rgbf.r = x; rgbf.g = c; rgbf.b = m; }
+    else if (h2 <  3.0f) { rgbf.r = m; rgbf.g = c; rgbf.b = x; }
+    else if (h2 <  4.0f) { rgbf.r = m; rgbf.g = x; rgbf.b = c; }
+    else if (h2 <  5.0f) { rgbf.r = x; rgbf.g = m; rgbf.b = c; }
+    else if (h2 <= 6.0f) { rgbf.r = c; rgbf.g = m; rgbf.b = x; }
+    
+    rgbf.a = hsl.a;
+
+    return rgbf;
+}
+
+/**
+ * get the corresponding hsl color to a given rgb color (integer).
+ *
+ * @param   rgb: the rgb color
+ *
+ * @return  the corresponding hsl color
+ */
+inline hsl_t
+rgb_to_hsl (rgb_t rgb)
+{
+    return rgbf_to_hsl (rgb_to_rgbf (rgb));
+}
+
+/**
+ * get the corresponding hsl color to a given rgb color (floating point). on
+ * error, errno is set and a zero-initialized struct is returned.
+ *
+ * @param   rgbf: the rgb color
+ *
+ * @return  the corresponding hsl color
+ *
+ * @errno   EINVAL: invalid rgb value passed
+ *
+ * @see     https://en.wikipedia.org/wiki/HSL_and_HSV#Color_conversion_formulae
+ */
+hsl_t
+rgbf_to_hsl (rgbf_t rgbf)
+{
+    f32 c, xmin, xmax;
+    hsl_t hsl;
+
+    if (rgbf.r < 0.0f || rgbf.r > 1.0f || rgbf.g < 0.0f || rgbf.g > 1.0f ||
+        rgbf.b < 0.0f || rgbf.b > 1.0f)
+        return errno = EINVAL, (hsl_t) {0};
+
+    xmax = fmaxf (rgbf.r, fmaxf (rgbf.g, rgbf.b));
+    xmin = fminf (rgbf.r, fminf (rgbf.g, rgbf.b));
+    c = xmax - xmin;
+    
+    if (c == 0.0f)
+        hsl.h = 0;
+    else if (xmax == rgbf.r)
+        hsl.h = (u8) lroundf (60.0f * fmodf (((rgbf.g - rgbf.b) / c), 6));
+    else if (xmax == rgbf.g)
+        hsl.h = (u8) lroundf (60.0f * (((rgbf.b - rgbf.r) / c) + 2.0f));
+    else if (xmax == rgbf.b)
+        hsl.h = (u8) lroundf (60.0f * (((rgbf.r - rgbf.g) / c) + 4.0f));
+
+    hsl.a = rgbf.a;
+    hsl.l = (xmax + xmin) / 2.0f;
+    hsl.s = (hsl.l == 0.0f || hsl.l == 1.0f)
+            ? 0.0f
+            : ((xmax - hsl.l) / fminf (hsl.l, 1.0f - hsl.l));
+
+    return hsl;
+}

lib/inc/color.h

@@ -0,0 +1,29 @@
+#ifndef COLOR_H_
+#define COLOR_H_
+
+#include "common.h"
+
+/* integer rgb struct, fields accept [0 .. 255] */
+typedef struct {
+    u8 r, g, b, a;
+} rgb_t;
+
+/* floating point rgb struct, fields accept [0.0f .. 1.0f] */
+typedef struct {
+    f32 r, g, b, a;
+} rgbf_t;
+
+/* hsl struct, h accepts [0 .. 360]; s, l, a accept [0.0f .. 1.0f] */
+typedef struct {
+    u16 h;
+    f32 s, l, a;
+} hsl_t;
+
+rgb_t rgbf_to_rgb (rgbf_t rgbf); /* turn a floating point rgb struct into an integer rbg struct */
+rgbf_t rgb_to_rgbf (rgb_t rgb); /* turn an integer rgb struct into a floating point rbg struct */
+rgb_t hsl_to_rgb (hsl_t hsl); /* get the corresponding rgb color (integer) to a given hsl color */
+rgbf_t hsl_to_rgbf (hsl_t hsl); /* get the corresponding rgb color (floating point) to a given hsl color */
+hsl_t rgb_to_hsl (rgb_t rgb); /* get the corresponding hsl color to a given rgb color (integer) */
+hsl_t rgbf_to_hsl (rgbf_t rgbf); /* get the corresponding hsl color to a given rgb color (floating point) */
+
+#endif // COLOR_H_

makefile

@@ -1,5 +1,6 @@
 CC := gcc
 CFLAGS := -Wall -Wextra -Werror=implicit -pedantic -Og -g -Ilib/inc
+CLIBS := -lm
 
 SRCFILES := $(wildcard lib/*.c)
 SRCFILES += $(wildcard test/*.c)
@@ -21,7 +22,7 @@ test: $(TARGET)
 
 
 $(TARGET): mkdir $(OBJFILES)
-	$(CC) $(CFLAGS) $(OBJFILES) -o $(TARGET)
+	$(CC) $(CFLAGS) $(CLIBS) $(OBJFILES) -o $(TARGET)
 
 obj/%.o: %.c
 	@$(CC) $(CFLAGS) $(DEPFLAGS) $<