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/* Visualize the standard VGA palette.
* Based on https://github.com/canidlogic/vgapal (MIT License) */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
char* bar(int n) {
char* result = calloc(1024, 32);
int i;
strcat(result, "<div style='float:left; width:40em'>");
for (i = 0; i < n; ++i)
//? result[i] = '.';
strcat(result, "■"); /* black square */
//? for (; i < 64; ++i)
//? result[i] = ' ';
//? result[64] = '\0';
strcat(result, " </div>"); /* make sure the div occupies space */
return result;
}
/* convert 6-bit color to 8-bit color */
int levelUp(int n) {
assert(n < 64);
/* duplicate two most significant bits in two least significant bits */
return (n<<2) | (n>>4);
}
void addColor(int r, int g, int b) {
static int i = 0;
//? printf("%02x %02x %02x\n", r, g, b);
//? printf("%3d: %2d %2d %2d %s %s %s\n", i, r, g, b, bar(r), bar(g), bar(b));
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));
++i;
}
void addGrayColor(int v) {
addColor(v, v, v);
}
void add16Color(int lo, int melo, int mehi, int hi) {
int r, g, b, i, h, l;
for (i = 0; i < 8; i++) {
r = g = b = lo;
if (i & 4) r = mehi;
if (i & 2) g = (i==6)?melo:mehi; /* exception: color 6 is brown rather than dark yellow */
if (i & 1) b = mehi;
addColor(r, g, b);
}
for (i = 0; i < 8; i++) {
r = g = b = melo;
if (i & 4) r = hi;
if (i & 2) g = hi;
if (i & 1) b = hi;
addColor(r, g, b);
}
}
/* Add four colors to the palette corresponding to a "run" within an RGB cycle.
*
* start - high and low starting states for each channel at the start of the run
* ch - the channel to change from high to low or low to high */
void addRun(int start, int ch, int lo, int melo, int me, int mehi, int hi) {
int r, g, b, i, up;
/* Check parameters */
if (start < 0 || start > 7)
abort();
if (ch != 1 && ch != 2 && ch != 4)
abort();
/* Get the starting RGB color and add it */
r = lo;
g = lo;
b = lo;
if ((start & 4) == 4)
r = hi;
if ((start & 2) == 2)
g = hi;
if ((start & 1) == 1)
b = hi;
addColor(r, g, b);
/* If selected channel starts high, we're going down; otherwise we're going up */
up = (start & ch) != ch;
/* Add remaining three colors of the run */
switch (ch) {
case 4: r = up?melo:mehi; break;
case 2: g = up?melo:mehi; break;
case 1: b = up?melo:mehi; break;
}
addColor(r, g, b);
switch (ch) {
case 4: r = me; break;
case 2: g = me; break;
case 1: b = me; break;
}
addColor(r, g, b);
switch (ch) {
case 4: r = up?mehi:melo; break;
case 2: g = up?mehi:melo; break;
case 1: b = up?mehi:melo; break;
}
addColor(r, g, b);
}
/* A cycle consists of six 4-color runs, each of which transitions from
* one hue to another until arriving back at starting position. */
void addCycle(int lo, int melo, int me, int mehi, int hi) {
int hue = 1; /* blue */
addRun(hue, 4, lo, melo, me, mehi, hi);
hue ^= 4;
assert(hue == 5);
addRun(hue, 1, lo, melo, me, mehi, hi);
hue ^= 1;
assert(hue == 4);
addRun(hue, 2, lo, melo, me, mehi, hi);
hue ^= 2;
assert(hue == 6);
addRun(hue, 4, lo, melo, me, mehi, hi);
hue ^= 4;
assert(hue == 2);
addRun(hue, 1, lo, melo, me, mehi, hi);
hue ^= 1;
assert(hue == 3);
addRun(hue, 2, lo, melo, me, mehi, hi);
}
int main(void) {
int i;
/* 16-color palette */
add16Color(0, 21, 42, 63);
/* 16 shades of gray */
addGrayColor( 0);
addGrayColor( 5);
addGrayColor( 8);
addGrayColor(11);
addGrayColor(14);
addGrayColor(17);
addGrayColor(20);
addGrayColor(24);
addGrayColor(28);
addGrayColor(32);
addGrayColor(36);
addGrayColor(40);
addGrayColor(45);
addGrayColor(50);
addGrayColor(56);
addGrayColor(63);
/* Nine RGB cycles organized in three groups of three cycles,
* The groups represent high/medium/low value,
* and the cycles within the groups represent high/medium/low saturation. */
addCycle( 0, 16, 31, 47, 63);
addCycle(31, 39, 47, 55, 63);
addCycle(45, 49, 54, 58, 63);
addCycle( 0, 7, 14, 21, 28);
addCycle(14, 17, 21, 24, 28);
addCycle(20, 22, 24, 26, 28);
addCycle( 0, 4, 8, 12, 16);
addCycle( 8, 10, 12, 14, 16);
addCycle(11, 12, 13, 15, 16);
/* final eight palette entries are full black */
for (i = 0; i < 8; ++i)
addGrayColor(0);
return 0;
}
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