winansi: more accurate colour mapping

Use a more accurate technique to map RGB colours to standard
Windows console colours.  Since this costs 648 bytes it's
configurable but is enabled by default.

4 files changed, 111 insertions, 22 deletions

diff --git a/Config.in b/Config.in
index 6d91ad248..356bc6d5a 100644
--- a/Config.in
+++ b/Config.in
@@ -472,6 +472,14 @@ config SKIP_ANSI_EMULATION_DEFAULT
         Setting the environment variable BB_SKIP_ANSI_EMULATION overrides
         this default.
 
+config FEATURE_IMPROVED_COLOUR_MAPPING
+        bool "More accurate colour mapping for ANSI emulation (0.6 kb)"
+        default y
+        depends on PLATFORM_MINGW32
+        help
+        Use a more accurate technique to map RGB colours to the standard
+        Windows console colours.
+
 config FEATURE_EXTRA_FILE_DATA
         bool "Read additional file metadata (2.1 kb)"
         default y
diff --git a/configs/mingw32_defconfig b/configs/mingw32_defconfig
index 51b27f366..f245141f3 100644
--- a/configs/mingw32_defconfig
+++ b/configs/mingw32_defconfig
@@ -1,7 +1,7 @@
 #
 # Automatically generated make config: don't edit
 # Busybox version: 1.34.0.git
-# Wed Feb  3 13:41:09 2021
+# Sun Feb  7 13:53:22 2021
 #
 CONFIG_HAVE_DOT_CONFIG=y
 # CONFIG_PLATFORM_POSIX is not set
@@ -53,6 +53,7 @@ CONFIG_FEATURE_ICON=y
 CONFIG_FEATURE_ICON_ALL=y
 CONFIG_FEATURE_EURO=y
 CONFIG_SKIP_ANSI_EMULATION_DEFAULT=2
+CONFIG_FEATURE_IMPROVED_COLOUR_MAPPING=y
 CONFIG_FEATURE_EXTRA_FILE_DATA=y
 CONFIG_FEATURE_READLINK2=y
 
diff --git a/configs/mingw64_defconfig b/configs/mingw64_defconfig
index a8cb75215..3ac1f7703 100644
--- a/configs/mingw64_defconfig
+++ b/configs/mingw64_defconfig
@@ -1,7 +1,7 @@
 #
 # Automatically generated make config: don't edit
 # Busybox version: 1.34.0.git
-# Wed Feb  3 13:41:09 2021
+# Sun Feb  7 13:53:22 2021
 #
 CONFIG_HAVE_DOT_CONFIG=y
 # CONFIG_PLATFORM_POSIX is not set
@@ -53,6 +53,7 @@ CONFIG_FEATURE_ICON=y
 CONFIG_FEATURE_ICON_ALL=y
 CONFIG_FEATURE_EURO=y
 CONFIG_SKIP_ANSI_EMULATION_DEFAULT=2
+CONFIG_FEATURE_IMPROVED_COLOUR_MAPPING=y
 CONFIG_FEATURE_EXTRA_FILE_DATA=y
 CONFIG_FEATURE_READLINK2=y
 
diff --git a/win32/winansi.c b/win32/winansi.c
index efb6efeb7..6120d5c28 100644
--- a/win32/winansi.c
+++ b/win32/winansi.c
@@ -262,6 +262,27 @@ static void move_cursor(int x, int y)
         SetConsoleCursorPosition(console, pos);
 }
 
+static const unsigned char colour_1bit[16] = {
+        /* Black */   0,
+        /* Red   */   FOREGROUND_RED,
+        /* Green */   FOREGROUND_GREEN,
+        /* Yellow */  FOREGROUND_RED | FOREGROUND_GREEN,
+        /* Blue */    FOREGROUND_BLUE,
+        /* Magenta */ FOREGROUND_RED | FOREGROUND_BLUE,
+        /* Cyan */    FOREGROUND_GREEN | FOREGROUND_BLUE,
+        /* White */   FOREGROUND_RED | FOREGROUND_GREEN | FOREGROUND_BLUE,
+        /* ... and again but brighter */
+        FOREGROUND_INTENSITY,
+        FOREGROUND_RED | FOREGROUND_INTENSITY,
+        FOREGROUND_GREEN | FOREGROUND_INTENSITY,
+        FOREGROUND_RED | FOREGROUND_GREEN | FOREGROUND_INTENSITY,
+        FOREGROUND_BLUE | FOREGROUND_INTENSITY,
+        FOREGROUND_RED | FOREGROUND_BLUE | FOREGROUND_INTENSITY,
+        FOREGROUND_GREEN | FOREGROUND_BLUE | FOREGROUND_INTENSITY,
+        FOREGROUND_RED | FOREGROUND_GREEN | FOREGROUND_BLUE | FOREGROUND_INTENSITY
+};
+
+#if !ENABLE_FEATURE_IMPROVED_COLOUR_MAPPING
 static WORD rgb_to_console(int *rgb)
 {
         int dark = 0, bright;
@@ -291,6 +312,84 @@ static WORD rgb_to_console(int *rgb)
 
         return attr;
 }
+#else
+#include <math.h>
+
+/* Standard console colours in LAB colour space */
+static float colour_lab[16][3] = {
+        {-0.000000, 0.000000, 0.000000},
+        {25.530788, 48.055233, 38.059635},
+        {46.228817, -51.699638, 49.897949},
+        {51.868336, -12.930751, 56.677288},
+        {12.975313, 47.507763, -64.704285},
+        {29.782101, 58.939846, -36.497940},
+        {48.256081, -28.841570, -8.481050},
+        {77.704361, 0.004262, -0.008416},
+        {53.585018, 0.003129, -0.006235},
+        {53.232883, 80.109299, 67.220078},
+        {87.737038, -86.184654, 83.181168},
+        {97.138245, -21.555901, 94.482483},
+        {32.302586, 79.196678, -107.863686},
+        {60.319931, 98.254234, -60.842991},
+        {91.116524, -48.079609, -14.138126},
+        {100.000000, 0.005245, -0.010419},
+};
+
+/* Convert RGB to XYZ and XYZ to LAB.  See:
+ * http://www.easyrgb.com/en/math.php#text1 */
+static void rgb2lab(const int *rgb, float *lab)
+{
+        float var_RGB[3], var_XYZ[3];
+        int i;
+
+        for (i = 0; i < 3; ++i) {
+                var_RGB[i] = rgb[i]/255.0;
+                if (var_RGB[i] > 0.04045)
+                        var_RGB[i] = pow(((var_RGB[i] + 0.055) / 1.055), 2.4);
+                else
+                        var_RGB[i] /= 12.92;
+        }
+
+        /* use equal energy reference values */
+        var_XYZ[0] = var_RGB[0]*0.4124 + var_RGB[1]*0.3576 + var_RGB[2]*0.1805;
+        var_XYZ[1] = var_RGB[0]*0.2126 + var_RGB[1]*0.7152 + var_RGB[2]*0.0722;
+        var_XYZ[2] = var_RGB[0]*0.0193 + var_RGB[1]*0.1192 + var_RGB[2]*0.9505;
+
+        for (i = 0; i < 3; ++i) {
+                if (var_XYZ[i] > 0.008856)
+                        var_XYZ[i] = pow(var_XYZ[i], 1.0 / 3.0);
+                else
+                        var_XYZ[i] = 7.787 * var_XYZ[i] + 16.0 / 116.0;
+        }
+
+        lab[0] = 116.0 * var_XYZ[1] - 16.0;
+        lab[1] = 500.0 * (var_XYZ[0] - var_XYZ[1]);
+        lab[2] = 200.0 * (var_XYZ[1] - var_XYZ[2]);
+}
+
+static WORD rgb_to_console(int *rgb)
+{
+        int i, imin = 0;
+        float deltamin = 1.0e20;
+
+        /* Use 1976 CIE deltaE to find closest console colour.  See:
+         * https://zschuessler.github.io/DeltaE/learn */
+        for (i = 0; i < 16; ++i) {
+                float lab[3], dl, da, db, delta;
+
+                rgb2lab(rgb, lab);
+                dl = colour_lab[i][0] - lab[0];
+                da = colour_lab[i][1] - lab[1];
+                db = colour_lab[i][2] - lab[2];
+                delta = dl * dl + da * da + db *db;
+                if (delta < deltamin) {
+                        imin = i;
+                        deltamin = delta;
+                }
+        }
+        return colour_1bit[imin];
+}
+#endif
 
 /* 24-bit colour */
 static char *process_24bit(char *str, WORD *attr)
@@ -308,26 +407,6 @@ static char *process_24bit(char *str, WORD *attr)
         return str;
 }
 
-static const unsigned char colour_1bit[16] = {
-        /* Black */   0,
-        /* Red   */   FOREGROUND_RED,
-        /* Green */   FOREGROUND_GREEN,
-        /* Yellow */  FOREGROUND_RED | FOREGROUND_GREEN,
-        /* Blue */    FOREGROUND_BLUE,
-        /* Magenta */ FOREGROUND_RED | FOREGROUND_BLUE,
-        /* Cyan */    FOREGROUND_GREEN | FOREGROUND_BLUE,
-        /* White */   FOREGROUND_RED | FOREGROUND_GREEN | FOREGROUND_BLUE,
-        /* ... and again but brighter */
-        FOREGROUND_INTENSITY,
-        FOREGROUND_RED | FOREGROUND_INTENSITY,
-        FOREGROUND_GREEN | FOREGROUND_INTENSITY,
-        FOREGROUND_RED | FOREGROUND_GREEN | FOREGROUND_INTENSITY,
-        FOREGROUND_BLUE | FOREGROUND_INTENSITY,
-        FOREGROUND_RED | FOREGROUND_BLUE | FOREGROUND_INTENSITY,
-        FOREGROUND_GREEN | FOREGROUND_BLUE | FOREGROUND_INTENSITY,
-        FOREGROUND_RED | FOREGROUND_GREEN | FOREGROUND_BLUE | FOREGROUND_INTENSITY
-};
-
 /* 8-bit colour */
 static char *process_8bit(char *str, WORD *attr)
 {