2015-08-04 10:33:09 (UTC-03:00)

Marcel Rodrigues <marcelgmr@gmail.com>

Add default palette.

diff --git a/README b/README
index 506c792..3563d0f 100644
--- a/README
+++ b/README
@@ -51,6 +51,12 @@ palette. The number of color entries must be 2 ^ depth, where 1 <= depth <= 8.
     };
     int depth = 2;          /* palette has 1 << 2 (i.e. 4) entries */
 
+If `palette` is NULL,  entries are taken from a default table  of 256 colors. If
+`depth` < 8,  the default table will  be truncated to the  appropriate size. The
+default table is composed  of the 16 standard VGA colors,  plus the 216 web-safe
+colors (all combinations of  RGB with only 6 valid values  per channel), plus 24
+grey colors equally spaced between black and white, excluding both.
+
 If the `loop` parameter is zero, the resulting GIF will loop forever. If it is a
 positive number, the  animation will be played that nuumber  of times. If `loop`
 is negative,  no looping  information is stored  in the GIF  file (for  most GIF

diff --git a/gifenc.c b/gifenc.c
index 8f5daf2..e948a3d 100644
--- a/gifenc.c
+++ b/gifenc.c
@@ -12,6 +12,25 @@
 /* helper to write a little-endian 16-bit number portably */
 #define write_num(fd, n) write((fd), (uint8_t []) {(n) & 0xFF, (n) >> 8}, 2)
 
+static uint8_t vga[0x30] = {
+    0x00, 0x00, 0x00,
+    0xAA, 0x00, 0x00,
+    0x00, 0xAA, 0x00,
+    0xAA, 0x55, 0x00,
+    0x00, 0x00, 0xAA,
+    0xAA, 0x00, 0xAA,
+    0x00, 0xAA, 0xAA,
+    0xAA, 0xAA, 0xAA,
+    0x55, 0x55, 0x55,
+    0xFF, 0x55, 0x55,
+    0x55, 0xFF, 0x55,
+    0xFF, 0xFF, 0x55,
+    0x55, 0x55, 0xFF,
+    0xFF, 0x55, 0xFF,
+    0x55, 0xFF, 0xFF,
+    0xFF, 0xFF, 0xFF,
+};
+
 struct Node {
     uint16_t key;
     struct Node *children[];
@@ -45,6 +64,7 @@ new_gif(
     uint8_t *palette, int depth, int loop
 )
 {
+    int i, r, g, b, v;
     GIF *gif = calloc(1, sizeof(*gif) + 2*width*height);
     if (!gif)
         goto no_gif;
@@ -59,7 +79,28 @@ new_gif(
     write_num(gif->fd, width);
     write_num(gif->fd, height);
     write(gif->fd, (uint8_t []) {0xF0 | (depth-1), 0x00, 0x00}, 3);
-    write(gif->fd, palette, 3 << depth);
+    if (palette) {
+        write(gif->fd, palette, 3 << depth);
+    } else if (depth <= 4) {
+        write(gif->fd, vga, 3 << depth);
+    } else {
+        write(gif->fd, vga, sizeof(vga));
+        i = sizeof(vga);
+        for (r = 0; r < 6; r++) {
+            for (g = 0; g < 6; g++) {
+                for (b = 0; b < 6; b++) {
+                    write(gif->fd, (uint8_t []) {r*51, g*51, b*51}, 3);
+                    if (++i == 1 << depth)
+                        goto done_gct;
+                }
+            }
+        }
+        for (i = 1; i <= 24; i++) {
+            v = i * 0xFF / 25;
+            write(gif->fd, (uint8_t []) {v, v, v}, 3);
+        }
+    }
+done_gct:
     if (loop >= 0 && loop <= 0xFFFF)
         put_loop(gif, (uint16_t) loop);
     return gif;