git.zerfleddert.de Git - rigol/blob - png.c

   1 #include <string.h>
   2 #include <stdint.h>
   3 #include <arpa/inet.h>
   4 #include <zlib.h>
   5
   6 #include "png.h"
   7
   8 /* Table of CRCs of all 8-bit messages. */
   9 static unsigned long crc_table[256];
  10
  11 /* Flag: has the table been computed? Initially false. */
  12 static int crc_table_computed = 0;
  13
  14 /* Make the table for a fast CRC. */
  15 static void make_crc_table(void)
  16 {
  17         unsigned long c;
  18         int n, k;
  19
  20         for (n = 0; n < 256; n++) {
  21                 c = (unsigned long) n;
  22                 for (k = 0; k < 8; k++) {
  23                         if (c & 1)
  24                                 c = 0xedb88320L ^ (c >> 1);
  25                         else
  26                                 c = c >> 1;
  27                 }
  28                 crc_table[n] = c;
  29         }
  30         crc_table_computed = 1;
  31 }
  32
  33 /* Update a running CRC with the bytes buf[0..len-1]--the CRC
  34    should be initialized to all 1's, and the transmitted value
  35    is the 1's complement of the final running CRC (see the
  36    crc() routine below). */
  37
  38 static unsigned long update_crc(unsigned long crc, unsigned char *buf,
  39                 int len)
  40 {
  41         unsigned long c = crc;
  42         int n;
  43
  44         if (!crc_table_computed)
  45                 make_crc_table();
  46         for (n = 0; n < len; n++) {
  47                 c = crc_table[(c ^ buf[n]) & 0xff] ^ (c >> 8);
  48         }
  49         return c;
  50 }
  51
  52 /* Return the CRC of the bytes buf[0..len-1]. */
  53 static unsigned long crc(unsigned char *buf, int len)
  54 {
  55         return update_crc(0xffffffffL, buf, len) ^ 0xffffffffL;
  56 }
  57
  58 unsigned char *lcd2png(unsigned char *lcd, int *len)
  59 {
  60         unsigned char screen_conv[320*234*3];
  61         unsigned char lut[256][3];
  62         unsigned char *image;
  63         unsigned char *outpos;
  64         static const unsigned char png[] = {137, 80, 78, 71, 13, 10, 26, 10};
  65         static unsigned char ihdr[] = {'I', 'H', 'D', 'R',
  66                 0x00, 0x00, 0x01, 0x40, /* 320 - Width */
  67                 0x00, 0x00, 0x00, 0xea, /* 234 - Height */
  68                 0x08, /* Bit depth */
  69                 0x02, /* RGB Truecolor, Colour type */
  70                 0x00, /* Deflate, Compression method */
  71                 0x00, /* None, Filter method */
  72                 0x00  /* No interlace, Interlace method */
  73                 };
  74         static unsigned char idat[] = {'I', 'D', 'A', 'T'};
  75         static unsigned char iend[] = {'I', 'E', 'N', 'D'};
  76         uint32_t l;
  77         int i;
  78         int toalloc = 0;
  79
  80         for(i = 0; i < 256; i++) {
  81                 lut[i][0] = ((i >> 6) * 0x55);
  82                 lut[i][1] = ((((i >> 3) & 7) * 0x49) >> 1);
  83                 lut[i][2] = (((i & 7) * 0x49) >> 1);
  84         }
  85
  86         for(i = 0; i < sizeof(screen_conv); i += 3) {
  87                 screen_conv[i] = lut[lcd[i/3]][0];
  88                 screen_conv[i+1] = lut[lcd[i/3]][1];
  89                 screen_conv[i+2] = lut[lcd[i/3]][2];
  90         }
  91
  92         image = malloc(320*234*2); /* TODO: FIXME! */
  93         outpos = image;
  94         memcpy(outpos, png, sizeof(png));
  95         outpos += sizeof(png);
  96
  97         l = htonl(sizeof(ihdr) - 4); /* "IHDR" is not counted */
  98         memcpy(outpos, &l, sizeof(l));
  99         outpos += sizeof(l);
 100         memcpy(outpos, ihdr, sizeof(ihdr));
 101         outpos += sizeof(ihdr);
 102         l = crc(ihdr, sizeof(ihdr));
 103         memcpy(outpos, &l, sizeof(l));
 104         outpos += sizeof(l);
 105
 106         l = htonl(sizeof(iend) - 4); /* "IEND" is not counted */
 107         memcpy(outpos, &l, sizeof(l));
 108         outpos += sizeof(l);
 109         memcpy(outpos, iend, sizeof(iend));
 110         outpos += sizeof(iend);
 111         l = crc(iend, sizeof(iend));
 112         memcpy(outpos, &l, sizeof(l));
 113         outpos += sizeof(l);
 114
 115         *len = (int)(outpos - image);
 116         return image;
 117 }