hsl: add our own implementations of rgb-to-hsl and hsl-to-rgb

* New function: rgb_to_hsl()
* New function: hsl_to_rgb()
* Replace XTerm’s hls_to_rgb() with our own, hsl_to_rgb().
* Ensure hue/lum/sat values are within range before calling
  hsl_to_rgb()

Note that sixels’ use the following primary hues:

*  blue:  0°
*  red:   120
*  green: 240°

While “standard” HSL uses:

*  red:   0°
*  green: 120°
*  blue:  240°

Thus, we need to adjust the sixel’s hue value before calling
hsl_to_rgb().

hsl.c

@@ -0,0 +1,89 @@
+#include "hsl.h"
+
+#include <math.h>
+
+#include "util.h"
+
+void
+rgb_to_hsl(uint32_t rgb, int *hue, int *sat, int *lum)
+{
+    double r = (double)((rgb >> 16) & 0xff) / 255.;
+    double g = (double)((rgb >> 8) & 0xff) / 255.;
+    double b = (double)((rgb >> 0) & 0xff) / 255.;
+
+    double x_max = max(max(r, g), b);
+    double x_min = min(min(r, g), b);
+    double V = x_max;
+
+    double C = x_max - x_min;
+    double L = (x_max + x_min) / 2.;
+
+    *lum = 100 * L;
+
+    if (C == 0.0)
+        *hue = 0;
+    else if (V == r)
+        *hue = 60. * (0. + (g - b) / C);
+    else if (V == g)
+        *hue = 60. * (2. + (b - r) / C);
+    else if (V == b)
+        *hue = 60. * (4. + (r - g) / C);
+    if (*hue < 0)
+        *hue += 360;
+
+    double S = C == 0.0
+        ? 0
+        : C / (1. - fabs(2. * L - 1.));
+    *sat = 100 * S;
+}
+
+uint32_t
+hsl_to_rgb(int hue, int sat, int lum)
+{
+    double L = lum / 100.0;
+    double S = sat / 100.0;
+    double C = (1. - fabs(2. * L - 1.)) * S;
+
+    double X = C * (1. - fabs(fmod((double)hue / 60., 2.) - 1.));
+    double m = L - C / 2.;
+
+    double r, g, b;
+    if (hue >= 0 && hue <= 60) {
+        r = C;
+        g = X;
+        b = 0.;
+    } else if (hue >= 60 && hue <= 120) {
+        r = X;
+        g = C;
+        b = 0.;
+    } else if (hue >= 120 && hue <= 180) {
+        r = 0.;
+        g = C;
+        b = X;
+    } else if (hue >= 180 && hue <= 240) {
+        r = 0.;
+        g = X;
+        b = C;
+    } else if (hue >= 240 && hue <= 300) {
+        r = X;
+        g = 0.;
+        b = C;
+    } else if (hue >= 300 && hue <= 360) {
+        r = C;
+        g = 0.;
+        b = X;
+    } else {
+        r = 0.;
+        g = 0.;
+        b = 0.;
+    }
+
+    r += m;
+    g += m;
+    b += m;
+
+    return (
+        (int)round(r * 255.) << 16 |
+        (int)round(g * 255.) << 8 |
+        (int)round(b * 255.) << 0);
+}

hsl.h

@@ -0,0 +1,6 @@
+#pragma once
+
+#include <stdint.h>
+
+void rgb_to_hsl(uint32_t rgb, int *hue, int *sat, int *lum);
+uint32_t hsl_to_rgb(int hue, int sat, int lum);

meson.build

@@ -111,6 +111,7 @@ executable(
   'extract.c', 'extract.h',
   'fdm.c', 'fdm.h',
   'grid.c', 'grid.h',
+  'hsl.c', 'hsl.h',
   'input.c', 'input.h',
   'log.c', 'log.h',
   'macros.h',
@@ -125,7 +126,6 @@ executable(
   'server.c', 'server.h',
   'shm.c', 'shm.h',
   'sixel.c', 'sixel.h',
-  'sixel-hls.c', 'sixel-hls.h',
   'slave.c', 'slave.h',
   'spawn.c', 'spawn.h',
   'terminal.c', 'terminal.h',

sixel-hls.c

@@ -1,117 +0,0 @@
-// sixel.c (part of mintty)
-// this function is derived from a part of graphics.c
-// in Xterm pl#310 originally written by Ross Combs.
-//
-// Copyright 2013,2014 by Ross Combs
-//
-//                         All Rights Reserved
-//
-// Permission is hereby granted, free of charge, to any person obtaining a
-// copy of this software and associated documentation files (the
-// "Software"), to deal in the Software without restriction, including
-// without limitation the rights to use, copy, modify, merge, publish,
-// distribute, sublicense, and/or sell copies of the Software, and to
-// permit persons to whom the Software is furnished to do so, subject to
-// the following conditions:
-//
-// The above copyright notice and this permission notice shall be included
-// in all copies or substantial portions of the Software.
-//
-// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
-// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
-// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
-// IN NO EVENT SHALL THE ABOVE LISTED COPYRIGHT HOLDER(S) BE LIABLE FOR ANY
-// CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
-// TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
-// SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
-//
-// Except as contained in this notice, the name(s) of the above copyright
-// holders shall not be used in advertising or otherwise to promote the
-// sale, use or other dealings in this Software without prior written
-// authorization.
-
-#include "sixel-hls.h"
-
-#define SIXEL_RGB(r, g, b) (((r) << 16) + ((g) << 8) +  (b))
-
-int
-hls_to_rgb(int hue, int lum, int sat)
-{
-    double hs = (hue + 240) % 360;
-    double hv = hs / 360.0;
-    double lv = lum / 100.0;
-    double sv = sat / 100.0;
-    double c, x, m, c2;
-    double r1, g1, b1;
-    int r, g, b;
-    int hpi;
-
-    if (sat == 0) {
-        r = g = b = lum * 255 / 100;
-        return SIXEL_RGB(r, g, b);
-    }
-
-    if ((c2 = ((2.0 * lv) - 1.0)) < 0.0) {
-        c2 = -c2;
-    }
-    c = (1.0 - c2) * sv;
-    hpi = (int) (hv * 6.0);
-    x = (hpi & 1) ? c : 0.0;
-    m = lv - 0.5 * c;
-
-    switch (hpi) {
-    case 0:
-        r1 = c;
-        g1 = x;
-        b1 = 0.0;
-        break;
-    case 1:
-        r1 = x;
-        g1 = c;
-        b1 = 0.0;
-        break;
-    case 2:
-        r1 = 0.0;
-        g1 = c;
-        b1 = x;
-        break;
-    case 3:
-        r1 = 0.0;
-        g1 = x;
-        b1 = c;
-        break;
-    case 4:
-        r1 = x;
-        g1 = 0.0;
-        b1 = c;
-        break;
-    case 5:
-        r1 = c;
-        g1 = 0.0;
-        b1 = x;
-        break;
-    default:
-        return SIXEL_RGB(255, 255, 255);
-    }
-
-    r = (int) ((r1 + m) * 100.0 + 0.5);
-    g = (int) ((g1 + m) * 100.0 + 0.5);
-    b = (int) ((b1 + m) * 100.0 + 0.5);
-
-    if (r < 0) {
-        r = 0;
-    } else if (r > 100) {
-        r = 100;
-    }
-    if (g < 0) {
-        g = 0;
-    } else if (g > 100) {
-        g = 100;
-    }
-    if (b < 0) {
-        b = 0;
-    } else if (b > 100) {
-        b = 100;
-    }
-    return SIXEL_RGB(r * 255 / 100, g * 255 / 100, b * 255 / 100);
-}

sixel-hls.h

@@ -1,9 +0,0 @@
-#pragma once
-
-/*
- * Primary color hues:
- *  blue:  0 degrees
- *  red:   120 degrees
- *  green: 240 degrees
- */
-int hls_to_rgb(int hue, int lum, int sat);

sixel.c

@@ -7,7 +7,7 @@
 #define LOG_ENABLE_DBG 0
 #include "log.h"
 #include "render.h"
-#include "sixel-hls.h"
+#include "hsl.h"
 #include "util.h"
 #include "xmalloc.h"
 
@@ -1052,23 +1052,42 @@ decgci(struct terminal *term, uint8_t c)
 
         if (nparams > 4) {
             unsigned format = term->sixel.params[1];
-            unsigned c1 = term->sixel.params[2];
+            int c1 = term->sixel.params[2];
-            unsigned c2 = term->sixel.params[3];
+            int c2 = term->sixel.params[3];
-            unsigned c3 = term->sixel.params[4];
+            int c3 = term->sixel.params[4];
 
             switch (format) {
             case 1: { /* HLS */
-                uint32_t rgb = hls_to_rgb(c1, c2, c3);
+                int hue = min(c1, 360);
+                int lum = min(c2, 100);
+                int sat = min(c3, 100);
+
+                /*
+                 * Sixel’s HLS use the following primary color hues:
+                 *  blue:  0°
+                 *  red:   120°
+                 *  green: 240°
+                 *
+                 * While “standard” HSL uses:
+                 *  red:   0°
+                 *  green: 120°
+                 *  blue:  240°
+                 */
+                hue = (hue + 240) % 360;
+
+                uint32_t rgb = hsl_to_rgb(hue, sat, lum);
+
                 LOG_DBG("setting palette #%d = HLS %hhu/%hhu/%hhu (0x%06x)",
-                        term->sixel.color_idx, c1, c2, c3, rgb);
+                        term->sixel.color_idx, hue, lum, sat, rgb);
+
                 term->sixel.palette[term->sixel.color_idx] = rgb;
                 break;
             }
 
             case 2: {  /* RGB */
-                uint8_t r = 255 * c1 / 100;
+                uint8_t r = 255 * min(c1, 100) / 100;
-                uint8_t g = 255 * c2 / 100;
+                uint8_t g = 255 * min(c2, 100) / 100;
-                uint8_t b = 255 * c3 / 100;
+                uint8_t b = 255 * min(c3, 100) / 100;
 
                 LOG_DBG("setting palette #%d = RGB %hhu/%hhu/%hhu",
                         term->sixel.color_idx, r, g, b);