core: add functions to convert RGB to terminal color (and vice versa)

src/gui/gui-color.c

@@ -31,6 +31,7 @@
 #include <signal.h>
 #include <time.h>
 #include <ctype.h>
+#include <limits.h>
 
 #include "../core/weechat.h"
 #include "../core/wee-config.h"
@@ -51,6 +52,54 @@ struct t_hashtable *gui_color_hash_palette_color = NULL;
 struct t_hashtable *gui_color_hash_palette_alias = NULL;
 struct t_weelist *gui_color_list_with_alias = NULL;
 
+/* terminal colors */
+int gui_color_term256[256] =
+{
+    0x000000, 0x800000, 0x008000, 0x808000, 0x000080, 0x800080,  /*   0-5   */
+    0x008080, 0xc0c0c0, 0x808080, 0xff0000, 0x00ff00, 0xffff00,  /*   6-11  */
+    0x0000ff, 0xff00ff, 0x00ffff, 0xffffff, 0x000000, 0x00005f,  /*  12-17  */
+    0x000087, 0x0000af, 0x0000d7, 0x0000ff, 0x005f00, 0x005f5f,  /*  18-23  */
+    0x005f87, 0x005faf, 0x005fd7, 0x005fff, 0x008700, 0x00875f,  /*  24-29  */
+    0x008787, 0x0087af, 0x0087d7, 0x0087ff, 0x00af00, 0x00af5f,  /*  30-35  */
+    0x00af87, 0x00afaf, 0x00afd7, 0x00afff, 0x00d700, 0x00d75f,  /*  36-41  */
+    0x00d787, 0x00d7af, 0x00d7d7, 0x00d7ff, 0x00ff00, 0x00ff5f,  /*  42-47  */
+    0x00ff87, 0x00ffaf, 0x00ffd7, 0x00ffff, 0x5f0000, 0x5f005f,  /*  48-53  */
+    0x5f0087, 0x5f00af, 0x5f00d7, 0x5f00ff, 0x5f5f00, 0x5f5f5f,  /*  54-59  */
+    0x5f5f87, 0x5f5faf, 0x5f5fd7, 0x5f5fff, 0x5f8700, 0x5f875f,  /*  60-65  */
+    0x5f8787, 0x5f87af, 0x5f87d7, 0x5f87ff, 0x5faf00, 0x5faf5f,  /*  66-71  */
+    0x5faf87, 0x5fafaf, 0x5fafd7, 0x5fafff, 0x5fd700, 0x5fd75f,  /*  72-77  */
+    0x5fd787, 0x5fd7af, 0x5fd7d7, 0x5fd7ff, 0x5fff00, 0x5fff5f,  /*  78-83  */
+    0x5fff87, 0x5fffaf, 0x5fffd7, 0x5fffff, 0x870000, 0x87005f,  /*  84-89  */
+    0x870087, 0x8700af, 0x8700d7, 0x8700ff, 0x875f00, 0x875f5f,  /*  90-95  */
+    0x875f87, 0x875faf, 0x875fd7, 0x875fff, 0x878700, 0x87875f,  /*  96-101 */
+    0x878787, 0x8787af, 0x8787d7, 0x8787ff, 0x87af00, 0x87af5f,  /* 102-107 */
+    0x87af87, 0x87afaf, 0x87afd7, 0x87afff, 0x87d700, 0x87d75f,  /* 108-113 */
+    0x87d787, 0x87d7af, 0x87d7d7, 0x87d7ff, 0x87ff00, 0x87ff5f,  /* 114-119 */
+    0x87ff87, 0x87ffaf, 0x87ffd7, 0x87ffff, 0xaf0000, 0xaf005f,  /* 120-125 */
+    0xaf0087, 0xaf00af, 0xaf00d7, 0xaf00ff, 0xaf5f00, 0xaf5f5f,  /* 126-131 */
+    0xaf5f87, 0xaf5faf, 0xaf5fd7, 0xaf5fff, 0xaf8700, 0xaf875f,  /* 132-137 */
+    0xaf8787, 0xaf87af, 0xaf87d7, 0xaf87ff, 0xafaf00, 0xafaf5f,  /* 138-143 */
+    0xafaf87, 0xafafaf, 0xafafd7, 0xafafff, 0xafd700, 0xafd75f,  /* 144-149 */
+    0xafd787, 0xafd7af, 0xafd7d7, 0xafd7ff, 0xafff00, 0xafff5f,  /* 150-155 */
+    0xafff87, 0xafffaf, 0xafffd7, 0xafffff, 0xd70000, 0xd7005f,  /* 156-161 */
+    0xd70087, 0xd700af, 0xd700d7, 0xd700ff, 0xd75f00, 0xd75f5f,  /* 162-167 */
+    0xd75f87, 0xd75faf, 0xd75fd7, 0xd75fff, 0xd78700, 0xd7875f,  /* 168-173 */
+    0xd78787, 0xd787af, 0xd787d7, 0xd787ff, 0xd7af00, 0xd7af5f,  /* 174-179 */
+    0xd7af87, 0xd7afaf, 0xd7afd7, 0xd7afff, 0xd7d700, 0xd7d75f,  /* 180-185 */
+    0xd7d787, 0xd7d7af, 0xd7d7d7, 0xd7d7ff, 0xd7ff00, 0xd7ff5f,  /* 186-191 */
+    0xd7ff87, 0xd7ffaf, 0xd7ffd7, 0xd7ffff, 0xff0000, 0xff005f,  /* 192-197 */
+    0xff0087, 0xff00af, 0xff00d7, 0xff00ff, 0xff5f00, 0xff5f5f,  /* 198-203 */
+    0xff5f87, 0xff5faf, 0xff5fd7, 0xff5fff, 0xff8700, 0xff875f,  /* 204-209 */
+    0xff8787, 0xff87af, 0xff87d7, 0xff87ff, 0xffaf00, 0xffaf5f,  /* 210-215 */
+    0xffaf87, 0xffafaf, 0xffafd7, 0xffafff, 0xffd700, 0xffd75f,  /* 216-221 */
+    0xffd787, 0xffd7af, 0xffd7d7, 0xffd7ff, 0xffff00, 0xffff5f,  /* 222-227 */
+    0xffff87, 0xffffaf, 0xffffd7, 0xffffff, 0x080808, 0x121212,  /* 228-233 */
+    0x1c1c1c, 0x262626, 0x303030, 0x3a3a3a, 0x444444, 0x4e4e4e,  /* 234-239 */
+    0x585858, 0x626262, 0x6c6c6c, 0x767676, 0x808080, 0x8a8a8a,  /* 240-245 */
+    0x949494, 0x9e9e9e, 0xa8a8a8, 0xb2b2b2, 0xbcbcbc, 0xc6c6c6,  /* 246-251 */
+    0xd0d0d0, 0xdadada, 0xe4e4e4, 0xeeeeee,                      /* 252-255 */
+};
+
 
 /*
  * Searches for a color with configuration option name.
@@ -400,6 +449,68 @@ gui_color_get_custom (const char *color_name)
     return color[index_color];
 }
 
+/*
+ * Converts a terminal color to its RGB value.
+ *
+ * Returns a RGB color as integer.
+ */
+
+int
+gui_color_convert_term_to_rgb (int color)
+{
+    if ((color < 0) || (color > 255))
+        return 0;
+
+    return gui_color_term256[color];
+}
+
+/*
+ * Converts a RGB color to the closest terminal color.
+ *
+ * Argument "limit" is the number of colors to check in the table of terminal
+ * colors (starting from 0). So for example 256 will return any of the 256
+ * colors, 16 will return a color between 0 and 15.
+ *
+ * Returns the closest terminal color (0-255).
+ */
+
+int
+gui_color_convert_rgb_to_term (int rgb, int limit)
+{
+    int i, r1, g1, b1, r2, g2, b2, diff, best_diff, best_color;
+
+    r1 = rgb >> 16;
+    g1 = (rgb >> 8) & 0xFF;
+    b1 = rgb & 0xFF;
+
+    best_diff = INT_MAX;
+    best_color = 0;
+
+    for (i = 0; i < limit; i++)
+    {
+        r2 = gui_color_term256[i] >> 16;
+        g2 = (gui_color_term256[i] >> 8) & 0xFF;
+        b2 = gui_color_term256[i] & 0xFF;
+
+        diff = ((r2 - r1) * (r2 - r1)) +
+            ((g2 - g1) * (g2 - g1)) +
+            ((b2 - b1) * (b2 - b1));
+
+        /* exact match! */
+        if (diff == 0)
+            return i;
+
+        if (diff < best_diff)
+        {
+            best_color = i;
+            best_diff = diff;
+        }
+    }
+
+    /* return the closest color */
+    return best_color;
+}
+
 /*
  * Removes WeeChat color codes from a message.
  *

src/gui/gui-color.h

@@ -170,6 +170,8 @@ extern int gui_color_attr_get_flag (char c);
 extern void gui_color_attr_build_string (int color, char *str_attr);
 extern const char *gui_color_get_custom (const char *color_name);
 extern char *gui_color_decode (const char *string, const char *replacement);
+extern int gui_color_convert_term_to_rgb (int color);
+extern int gui_color_convert_rgb_to_term (int rgb, int limit);
 extern char *gui_color_emphasize (const char *string, const char *search,
                                   int case_sensitive, regex_t *regex);
 extern void gui_color_free (struct t_gui_color *color);