//--------------------------------------
//--- 010 Editor v2.0.1 Binary Template
//
//    File: PNGTemplate.bt
//  Author: Kevin O. Grover <kogrover@yahoo.com>
// Purpose: A template for parsing PNG (Portable Network Graphics) files.
//    Date: 2005-05-11
// History:
// 2005-05-11  KOG  Initial version
//
// This template was written to the PNG 1.2 Specification.
// Note however, then it does not check nor parse chunk subdata, so it
// should work with all future PNG specifications.
//
// Also, a possible caveat: PNG encourages the type of chunks to be
// mapped to string of "[a-zA-Z]{4}".  However, it's not a requirement.
//
// A PNG file consists of an 8 byte ID followed by a series of chunks.
//--------------------------------------

BigEndian();                  // PNG files are in Network Byte order

const uint64 PNGMAGIC = 0x89504E470D0A1A0AL;

// Chunk Type
typedef union {
  uint32  ctype <format=hex>; // Chunk Type
  char    cname[4];           // character representation
} CTYPE <read=readCTYPE>;

string readCTYPE(local CTYPE &t) {
  return t.cname;
}

// Chunks
typedef struct {
  uint32  length;             // Number of data bytes (not including length,type, or crc)
  CTYPE   type;               // Type of chunk
  ubyte   data[length];       // Data (or not present)
  uint32  crc <format=hex>;   // CRC type and data (not including length or crc)
} CHUNK <read=readCHUNK>;

// Chunks can be in any order: HOWEVER, IHDR must be first, IEND must be last
// Bit 5s in chunk type bytes are used to flag some things:
//    Ancillary bit: bit 5 of 1st byte: 0=Critical, 1=Ancillary
//      Private bit: bit 5 of 2nd byte: 0=Public, 1=Private
//     Reserved bit: bit 5 of 3rd byte: MUST be 0
// Safe to Copy bit: bit 5 of 4th byte: 0=Unsafe to Copy, 1=Safe to Copy
string readCHUNK(local CHUNK &c) {
  local string s;
  s=readCTYPE(c.type)+"  (";
  s += (c.type.cname[0] & 0x20) ? "Ancillary, "      : "Critical, "; 
  s += (c.type.cname[1] & 0x20) ? "Private, "        : "Public, ";
  s += (c.type.cname[2] & 0x20) ? "ERROR_RESERVED, " : "";
  s += (c.type.cname[3] & 0x20) ? "Safe to Copy)"    : "Unsafe to Copy)";
  return s;
}

// ---------------------------------------------------------------------------
// MAIN  --  Here's where we really allocate the data
// ---------------------------------------------------------------------------

uint64 pngid <format=hex>;
if (pngid != PNGMAGIC) {
  Warning("Invalid PNG File: Bad Magic Number"); return -1;
}
while(!FEof()) {
  CHUNK chunk;
}