RBG png generation

1 files changed, 166 insertions, 0 deletions

diff --git a/daemon.c b/daemon.c
index 434515a..0b44602 100644
--- a/daemon.c
+++ b/daemon.c
@@ -293,12 +293,178 @@ handler (GThreadedSocketService *service,
   return res;
 }
 
+/* Table of CRCs of all 8-bit messages. */
+static unsigned long crc_table[256];
+
+/* Flag: has the table been computed? Initially false. */
+static int crc_table_computed = 0;
+
+/* Make the table for a fast CRC. */
+static void
+make_crc_table(void)
+{
+  unsigned long c;
+  int n, k;
+
+  for (n = 0; n < 256; n++) {
+    c = (unsigned long) n;
+    for (k = 0; k < 8; k++) {
+      if (c & 1)
+	c = 0xedb88320L ^ (c >> 1);
+      else
+	c = c >> 1;
+    }
+    crc_table[n] = c;
+  }
+  crc_table_computed = 1;
+}
+
+static unsigned long
+update_crc(unsigned long crc, unsigned char *buf, int len)
+{
+  unsigned long c = crc;
+  int n;
+
+  if (!crc_table_computed)
+    make_crc_table();
+  for (n = 0; n < len; n++) {
+    c = crc_table[(c ^ buf[n]) & 0xff] ^ (c >> 8);
+  }
+  return c;
+}
+
+static unsigned long
+crc(unsigned char *buf, int len)
+{
+  return update_crc(0xffffffffL, buf, len) ^ 0xffffffffL;
+}
+
+#define BASE 65521 /* largest prime smaller than 65536 */
+static unsigned long
+update_adler32(unsigned long adler, unsigned char *buf, int len)
+{
+  unsigned long s1 = adler & 0xffff;
+  unsigned long s2 = (adler >> 16) & 0xffff;
+  int n;
+
+  for (n = 0; n < len; n++) {
+    s1 = (s1 + buf[n]) % BASE;
+    s2 = (s2 + s1)     % BASE;
+  }
+  return (s2 << 16) + s1;
+}
+
+/* Return the adler32 of the bytes buf[0..len-1] */
+
+static unsigned long adler32(unsigned char *buf, int len)
+{
+  return update_adler32(1L, buf, len);
+}
+
+guchar *
+to_png_rgb (int w, int h, int stride, guint32 *data, gsize *size_out)
+{
+  guchar header[] = {137, 80, 78, 71, 13, 10, 26, 10};
+  guchar ihdr[13+12] = {0, 0, 0, 13, 'I', 'H', 'D', 'R',
+			/* w: */ 0, 0, 0, 0, /* h: */ 0,0,0,0,
+			/* bpp: */ 8, /* color type: */ 2,
+			0, 0, 0};
+  guchar idat_start[8] = { /* len: */0, 0, 0, 0,   'I', 'D', 'A', 'T' };
+  guchar iend[12] = {0, 0, 0, 0, 'I', 'E', 'N', 'D', 0xae, 0x42, 0x60, 0x82};
+  gsize data_size, row_size;
+  char row_header[6];
+  guint8 *png, *p, *p_row, *p_idat;
+  guint32 *row;
+  unsigned long adler;
+  guint32 pixel;
+  int x, y;
+
+  *(guint32 *)&ihdr[8] = GUINT32_TO_BE(w);
+  *(guint32 *)&ihdr[12] = GUINT32_TO_BE(h);
+  *(guint32 *)&ihdr[21] = GUINT32_TO_BE(crc(&ihdr[4], 13 + 4));
+
+  row_size = 1 + w * 3;
+  row_header[0] = 0;
+  row_header[1] = row_size & 0xff;
+  row_header[2] = (row_size >> 8) & 0xff;
+  row_header[3] = ~row_header[1];
+  row_header[4] = ~row_header[2];
+  row_header[5] = 0;
+
+  data_size = 2 + (6 + w * 3) * h + 4;
+
+  *(guint32 *)&idat_start[0] = GUINT32_TO_BE(data_size);
+
+  *size_out = sizeof(header) + sizeof(ihdr) + 12 + data_size + sizeof(iend);
+  png = g_malloc (*size_out);
+
+  p = png;
+  memcpy (p, header, sizeof(header));
+  p += sizeof(header);
+  memcpy (p, ihdr, sizeof(ihdr));
+  p += sizeof(ihdr);
+  memcpy (p, idat_start, sizeof(idat_start));
+  p += sizeof(idat_start);
+
+  /* IDAT data:
+
+     zlib header:  0x78, 0x01 ,
+     h * scanline: row_header[] + width * r,g,b
+     checksum: adler32
+  */
+
+  p_idat = p - 4;
+
+  /* zlib header */
+  *p++ = 0x78;
+  *p++ = 0x01;
+
+  adler = 1;
+
+  /* scanline data */
+  for (y = 0; y < h; y++) {
+    if (y == h - 1)
+      row_header[0] = 1; /* final block */
+    memcpy (p, row_header, sizeof(row_header));
+    p += sizeof(row_header);
+    p_row = p - 1;
+    row = data;
+    data += stride;
+    for (x = 0; x < w; x++) {
+      pixel = *row++;
+      *p++ = (pixel >> 16) & 0xff; /* red */
+      *p++ = (pixel >> 8) & 0xff; /* green */
+      *p++ = (pixel >> 0) & 0xff; /* blue */
+    }
+    adler = update_adler32(adler, p_row, p - p_row);
+  }
+
+  /* adler32 */
+  *(guint32 *)p = GUINT32_TO_BE(adler);
+  p += 4;
+  *(guint32 *)p = GUINT32_TO_BE(crc(p_idat, p - p_idat));
+  p += 4;
+
+  memcpy (p, iend, sizeof(iend));
+  p += sizeof(iend);
+
+  g_assert(p - png == *size_out);
+
+  return png;
+}
+
 int
 main (int argc, char *argv[])
 {
   GSocketService *service;
   GOptionContext *context;
   GError *error = NULL;
+  guint32 pixel[4] = {0xffffff, 0xff0000, 0xff00ff, 0x00ff00};
+  guchar *data;
+  gsize data_size;
+
+  data = to_png_rgb (2, 2, 2, pixel, &data_size);
+  //g_file_set_contents ("mini.png", (char *)data, data_size, NULL);
 
   g_type_init ();
   g_thread_init (NULL);