added hsv gradient

src/colours.cc

@@ -36,6 +36,18 @@
 #define CONST_8_TO_5_BITS 0.12156862745098
 #define CONST_8_TO_6_BITS 0.247058823529412
 
+#define CONST_SCALE 512L
+#define CONST_SCALE_HALF (CONST_SCALE / 2)
+#define CONST_SCALE2 (CONST_SCALE * 2L)
+#define CONST_SCALE4 (CONST_SCALE * 4L)
+#define CONST_SCALE6 (CONST_SCALE * 6L)
+#define CONST_SCALE60 (CONST_SCALE * 60L)
+#define CONST_SCALE120 (CONST_SCALE * 120L)
+#define CONST_SCALE180 (CONST_SCALE * 180L)
+#define CONST_SCALE240 (CONST_SCALE * 240L)
+#define CONST_SCALE300 (CONST_SCALE * 300L)
+#define CONST_SCALE360 (CONST_SCALE * 360L)
+
 static short colour_depth = 0;
 static long redmask, greenmask, bluemask;
 
@@ -144,6 +156,160 @@ unsigned long *do_gradient(int width, unsigned long first_colour,
   return colours;
 }
 
+long to_decimal_scale(long value, long max_value) {
+  if (value == 0) {
+    return 0;
+  } else if (value > 0) {
+    return (value * CONST_SCALE + max_value - 1) / max_value;
+  }
+  return -((abs(value) * CONST_SCALE  + max_value - 1) / max_value);
+}
+
+long from_decimal_scale(long value, long max_value) {
+  if (value == 0) {
+    return 0;
+  } else if (value > 0) {
+    return (value * max_value + CONST_SCALE_HALF) / CONST_SCALE;
+  }
+  return -((abs(value) * max_value + CONST_SCALE_HALF) / CONST_SCALE);
+}
+
+void scaled_rgb_to_scaled_hsv(long * const rgb, long *hsv) {
+  long val = rgb[0] > rgb[1] ? MAX(rgb[0], rgb[2]) : MAX(rgb[1], rgb[2]);
+  long cmin = rgb[0] < rgb[1] ? MIN(rgb[0], rgb[2]) : MIN(rgb[1], rgb[2]);
+  long delta = val - cmin;
+
+  long hue;
+
+  if (delta == 0) {
+    hue = 0;
+  } else {
+    long d;
+    long offset;
+
+    if (rgb[0] == val) {
+      d = rgb[1] - rgb[2];
+      offset = 0;
+    } else if (rgb[1] == val) {
+      d = rgb[2] - rgb[0];
+      offset = CONST_SCALE2;
+    } else {
+      d = rgb[0] - rgb[1];
+      offset = CONST_SCALE4;
+    }
+    long h = (CONST_SCALE * d + delta / 2) / delta + offset;
+    hue = 60L * ((CONST_SCALE6 + h) % CONST_SCALE6);
+  }
+
+  long sat;
+  if (val == 0) {
+    sat = 0;
+  } else {
+    sat = (CONST_SCALE * delta + val / 2) / val;
+  }
+
+  hsv[0] = hue;
+  hsv[1] = sat;
+  hsv[2] = val;
+}
+
+void scaled_hsv_to_scaled_rgb(long *const hsv, long *rgb) {
+  long c = (hsv[2] * hsv[1] + CONST_SCALE_HALF) / CONST_SCALE;
+
+  long hue = hsv[0] % CONST_SCALE360;
+  long x = (c *
+      (CONST_SCALE - abs(((hue + 30L) / 60L) % CONST_SCALE2 - CONST_SCALE))
+      + CONST_SCALE_HALF) / CONST_SCALE;
+  long m = hsv[2] - c;
+
+  rgb[0] = m;
+  rgb[1] = m;
+  rgb[2] = m;
+
+  if (hue < CONST_SCALE60) {
+    rgb[0] += c;
+    rgb[1] += x;
+  } else if (hue < CONST_SCALE120) {
+    rgb[0] += x;
+    rgb[1] += c;
+  } else if (hue < CONST_SCALE180) {
+    rgb[1] += c;
+    rgb[2] += x;
+  } else if (hue < CONST_SCALE240) {
+    rgb[1] += x;
+    rgb[2] += c;
+  } else if (hue < CONST_SCALE300) {
+    rgb[2] += c;
+    rgb[0] += x;
+  } else {
+    rgb[2] += x;
+    rgb[0] += c;
+  }
+}
+
+/* this function returns the next colour between two colours in hsv space for a gradient */
+unsigned long *do_hsv_gradient(
+    int width,
+    unsigned long first_colour,
+    unsigned long last_colour) {
+
+  long rgb1[3], rgb2[3], rgb3[3];
+  long hsv1[3], hsv2[3];
+  long hueDiff, satDiff, valDiff;
+
+  int redshift = (2 * colour_depth / 3 + colour_depth % 3);
+  int greenshift = (colour_depth / 3);
+  auto *colours =
+      static_cast<unsigned long *>(malloc(width * sizeof(unsigned long)));
+  int i;
+
+  if (colour_depth == 0) { set_up_gradient(); }
+
+  rgb1[0] = to_decimal_scale((first_colour & redmask) >> redshift, redmask >> redshift);
+  rgb1[1] = to_decimal_scale((first_colour & greenmask) >> greenshift, greenmask >> greenshift);
+  rgb1[2] = to_decimal_scale(first_colour & bluemask, bluemask);
+  rgb2[0] = to_decimal_scale((last_colour & redmask) >> redshift, redmask >> redshift);
+  rgb2[1] = to_decimal_scale((last_colour & greenmask) >> greenshift, greenmask >> greenshift);
+  rgb2[2] = to_decimal_scale(last_colour & bluemask, bluemask);
+
+  scaled_rgb_to_scaled_hsv(rgb1, hsv1);
+  scaled_rgb_to_scaled_hsv(rgb2, hsv2);
+
+  hueDiff = hsv2[0] - hsv1[0];
+  satDiff = hsv2[1] - hsv1[1];
+  valDiff = hsv2[2] - hsv1[2];
+
+  colours[0] = first_colour;
+  colours[width - 1] = last_colour;
+
+  for (i = 1; i < (width - 1); i++) {
+    long k;
+
+    long divisor = width - i;
+    k = (hueDiff + divisor / 2) / divisor;
+    hueDiff -= k;
+    hsv1[0] += k;
+
+    k = (satDiff + divisor / 2) / divisor;
+    satDiff -= k;
+    hsv1[1] += k;
+
+    k = (valDiff + divisor / 2) / divisor;
+    valDiff -= k;
+    hsv1[2] += k;
+
+    scaled_hsv_to_scaled_rgb(hsv1, rgb3);
+
+    long red3 = from_decimal_scale(rgb3[0], bluemask);
+    long green3 = from_decimal_scale(rgb3[1], bluemask);
+    long blue3 = from_decimal_scale(rgb3[2], bluemask);
+
+    colours[i] = (red3 << redshift) | (green3 << greenshift) | blue3;
+
+  }
+  return colours;
+}
+
 #ifdef BUILD_X11
 long get_x11_color(const char *name) {
   XColor color;

src/colours.h

@@ -33,6 +33,7 @@
 
 unsigned int adjust_colours(unsigned int);
 unsigned long *do_gradient(int, unsigned long, unsigned long);
+unsigned long *do_hsv_gradient(int, unsigned long, unsigned long);
 
 long get_x11_color(const std::string &colour);
 // XXX: when everyone uses C++ strings, remove this C version