tools/vga_palette.c

   1 /* Visualize the standard VGA palette.
   2  * Based on https://github.com/canidlogic/vgapal (MIT License) */
   3
   4 #include <stdio.h>
   5 #include <stdlib.h>
   6 #include <string.h>
   7 #include <assert.h>
   8
   9 char* bar(int n) {
  10   char* result = calloc(1024, 32);
  11   int i;
  12   strcat(result, "<div style='float:left; width:40em'>");
  13   for (i = 0; i < n; ++i)
  14 //?     result[i] = '.';
  15     strcat(result, "&#9632;");  /* black square */
  16 //?   for (; i < 64; ++i)
  17 //?     result[i] = ' ';
  18 //?   result[64] = '\0';
  19   strcat(result, "&nbsp;</div>");  /* make sure the div occupies space */
  20   return result;
  21 }
  22
  23 /* convert 6-bit color to 8-bit color */
  24 int levelUp(int n) {
  25   assert(n < 64);
  26   /* duplicate two most significant bits in two least significant bits */
  27   return (n<<2) | (n>>4);
  28 }
  29
  30 void addColor(int r, int g, int b) {
  31   static int i = 0;
  32 //?   printf("%02x %02x %02x\n", r, g, b);
  33 //?   printf("%3d: %2d %2d %2d %s %s %s\n", i, r, g, b, bar(r), bar(g), bar(b));
  34   printf("<div style='clear:both; white-space:pre; color:#%02x%02x%02x'><div style='float:left; margin-right:1em'>%03d: %02d %02d %02d</div> %s %s %s</div>\n", levelUp(r), levelUp(g), levelUp(b), i, r, g, b, bar(r), bar(g), bar(b));
  35   ++i;
  36 }
  37
  38 void addGrayColor(int v) {
  39   addColor(v, v, v);
  40 }
  41
  42 void add16Color(int lo, int melo, int mehi, int hi) {
  43   int r, g, b, i, h, l;
  44
  45   for (i = 0; i < 8; i++) {
  46     r = g = b = lo;
  47     if (i & 4) r = mehi;
  48     if (i & 2) g = (i==6)?melo:mehi;  /* exception: color 6 is brown rather than dark yellow */
  49     if (i & 1) b = mehi;
  50     addColor(r, g, b);
  51   }
  52
  53   for (i = 0; i < 8; i++) {
  54     r = g = b = melo;
  55     if (i & 4) r = hi;
  56     if (i & 2) g = hi;
  57     if (i & 1) b = hi;
  58     addColor(r, g, b);
  59   }
  60 }
  61
  62 /* Add four colors to the palette corresponding to a "run" within an RGB cycle.
  63  *
  64  * start - high and low starting states for each channel at the start of the run
  65  * ch - the channel to change from high to low or low to high */
  66 void addRun(int start, int ch, int lo, int melo, int me, int mehi, int hi) {
  67   int r, g, b, i, up;
  68
  69   /* Check parameters */
  70   if (start < 0 || start > 7)
  71     abort();
  72   if (ch != 1 && ch != 2 && ch != 4)
  73     abort();
  74
  75   /* Get the starting RGB color and add it */
  76   r = lo;
  77   g = lo;
  78   b = lo;
  79   if ((start & 4) == 4)
  80     r = hi;
  81   if ((start & 2) == 2)
  82     g = hi;
  83   if ((start & 1) == 1)
  84     b = hi;
  85   addColor(r, g, b);
  86
  87   /* If selected channel starts high, we're going down; otherwise we're going up */
  88   up = (start & ch) != ch;
  89
  90   /* Add remaining three colors of the run */
  91   switch (ch) {
  92   case 4:  r = up?melo:mehi; break;
  93   case 2:  g = up?melo:mehi; break;
  94   case 1:  b = up?melo:mehi; break;
  95   }
  96   addColor(r, g, b);
  97
  98   switch (ch) {
  99   case 4:  r = me; break;
 100   case 2:  g = me; break;
 101   case 1:  b = me; break;
 102   }
 103   addColor(r, g, b);
 104
 105   switch (ch) {
 106   case 4:  r = up?mehi:melo; break;
 107   case 2:  g = up?mehi:melo; break;
 108   case 1:  b = up?mehi:melo; break;
 109   }
 110   addColor(r, g, b);
 111 }
 112
 113 /* A cycle consists of six 4-color runs, each of which transitions from
 114  * one hue to another until arriving back at starting position. */
 115 void addCycle(int lo, int melo, int me, int mehi, int hi) {
 116   int hue = 1;  /* blue */
 117   addRun(hue, 4, lo, melo, me, mehi, hi);
 118   hue ^= 4;
 119   assert(hue == 5);
 120   addRun(hue, 1, lo, melo, me, mehi, hi);
 121   hue ^= 1;
 122   assert(hue == 4);
 123   addRun(hue, 2, lo, melo, me, mehi, hi);
 124   hue ^= 2;
 125   assert(hue == 6);
 126   addRun(hue, 4, lo, melo, me, mehi, hi);
 127   hue ^= 4;
 128   assert(hue == 2);
 129   addRun(hue, 1, lo, melo, me, mehi, hi);
 130   hue ^= 1;
 131   assert(hue == 3);
 132   addRun(hue, 2, lo, melo, me, mehi, hi);
 133 }
 134
 135 int main(void) {
 136   int i;
 137
 138   /* 16-color palette */
 139   add16Color(0, 21, 42, 63);
 140
 141   /* 16 shades of gray */
 142   addGrayColor( 0);
 143   addGrayColor( 5);
 144   addGrayColor( 8);
 145   addGrayColor(11);
 146   addGrayColor(14);
 147   addGrayColor(17);
 148   addGrayColor(20);
 149   addGrayColor(24);
 150   addGrayColor(28);
 151   addGrayColor(32);
 152   addGrayColor(36);
 153   addGrayColor(40);
 154   addGrayColor(45);
 155   addGrayColor(50);
 156   addGrayColor(56);
 157   addGrayColor(63);
 158
 159   /* Nine RGB cycles organized in three groups of three cycles,
 160    * The groups represent high/medium/low value,
 161    * and the cycles within the groups represent high/medium/low saturation. */
 162   addCycle( 0, 16, 31, 47, 63);
 163   addCycle(31, 39, 47, 55, 63);
 164   addCycle(45, 49, 54, 58, 63);
 165
 166   addCycle( 0,  7, 14, 21, 28);
 167   addCycle(14, 17, 21, 24, 28);
 168   addCycle(20, 22, 24, 26, 28);
 169
 170   addCycle( 0,  4,  8, 12, 16);
 171   addCycle( 8, 10, 12, 14, 16);
 172   addCycle(11, 12, 13, 15, 16);
 173
 174   /* final eight palette entries are full black */
 175   for (i = 0; i < 8; ++i)
 176     addGrayColor(0);
 177
 178   return 0;
 179 }