First commit - moving from LuaForge to SourceForge

1 files changed, 1497 insertions, 0 deletions

diff --git a/src/im_format_gif.cpp b/src/im_format_gif.cpp
new file mode 100644
index 0000000..ce371ba
--- /dev/null
+++ b/src/im_format_gif.cpp
@@ -0,0 +1,1497 @@
+/** \file
+ * \brief GIF - Graphics Interchange Format
+ *
+ * See Copyright Notice in im_lib.h
+ * $Id: im_format_gif.cpp,v 1.1 2008/10/17 06:10:16 scuri Exp $
+ */
+
+#include "im_format.h"
+#include "im_format_all.h"
+#include "im_util.h"
+#include "im_counter.h"
+
+#include "im_binfile.h"
+
+#include <stdlib.h>
+#include <string.h>
+#include <setjmp.h>
+
+static const int InterlacedOffset[4] = { 0, 4, 2, 1 },  /* The way Interlaced image should */
+	               InterlacedJumps[4]  = { 8, 8, 4, 2 };  /* be read - offsets and jumps... */
+
+#define GIF_STAMP	  "GIF"	 /* First chars in file - GIF stamp. */
+#define GIF_VERSION	"89a"	 /* First chars in file - GIF stamp. */
+ 
+#define GIF_LZ_BITS		12
+
+#define GIF_LZ_MAX_CODE	    4095		/* Biggest code possible in 12 bits. */
+#define GIF_FLUSH_OUTPUT		4096    /* Impossible code, to signal flush. */
+#define GIF_FIRST_CODE		  4097    /* Impossible code, to signal first. */
+#define GIF_NO_SUCH_CODE		4098    /* Impossible code, to signal empty. */
+
+#define GIF_HT_KEY_MASK		0x1FFF		/* 13bits keys */
+#define GIF_HT_KEY_NUM_BITS		13		/* 13bits keys */
+#define GIF_HT_MAX_KEY		  8191	  /* 13bits - 1, maximal code possible */
+#define GIF_HT_SIZE			    8192	  /* 12bits = 4096 or twice as big! */
+
+/*  GIF89 extension function codes                                             */
+#define COMMENT_EXT_FUNC_CODE	    0xFE	/* comment */
+#define GRAPHICS_EXT_FUNC_CODE    0xF9	/* graphics control */
+#define PLAINTEXT_EXT_FUNC_CODE   0x01	/* plaintext */
+#define APPLICATION_EXT_FUNC_CODE 0xFF	/* application block */
+
+/* The 32 bits of the integer are divided into two parts for the key & code:   */
+/* 1. The code is 12 bits as our compression algorithm is limited to 12bits */
+/* 2. The key is 12 bits Prefix code + 8 bit new char or 20 bits.	    */
+#define GIF_HT_GET_KEY(l)	(l >> 12)
+#define GIF_HT_GET_CODE(l)	(l & 0x0FFF)
+#define GIF_HT_PUT_KEY(l)	(l << 12)
+#define GIF_HT_PUT_CODE(l)	(l & 0x0FFF)
+
+struct iGIFData
+{
+  unsigned char global_colors[256 * 3]; /* global color table if any */
+  int global_num_colors, /* global color table number of colors */
+      offset,            /* image offset */
+      step,              /* interlaced step */
+      interlaced,        /* image is interlaced or not */
+      screen_width,
+      screen_height,
+      start_offset[512], /* offset of first block */
+	    ClearCode,				 /* The CLEAR LZ code. */
+    	BitsPerPixel,	     /* Bits per pixel (Codes uses at list this + 1). */
+	    EOFCode,				   /* The EOF LZ code. */
+	    RunningCode,		   /* The next code algorithm can generate. */
+	    RunningBits,       /* The number of bits required to represent RunningCode. */
+	    MaxCode1,          /* 1 bigger than max. possible code, in RunningBits bits. */
+	    LastCode,		       /* The code before the current code. */
+	    CrntCode,				   /* Current algorithm code. */
+	    StackPtr,		       /* For character stack (see below). */
+	    CrntShiftState;		 /* Number of bits in CrntShiftDWord. */
+  unsigned char Buf[256];	                  /* Compressed input is buffered here. */
+  unsigned int CrntShiftDWord;             /* For bytes decomposition into codes. */
+  unsigned char Stack[GIF_LZ_MAX_CODE];	    /* Decoded pixels are stacked here. */
+  unsigned char Suffix[GIF_LZ_MAX_CODE+1];	/* So we can trace the codes. */
+  unsigned int Prefix[GIF_LZ_MAX_CODE+1];
+  unsigned int HTable[GIF_HT_SIZE];            /* hash table for the compression only, when using LZW */
+};
+
+/******************************************************************************
+* Routine to generate an HKey for the hashtable out of the given unique key.  *
+* The given Key is assumed to be 20 bits as follows: lower 8 bits are the     *
+* new postfix character, while the upper 12 bits are the prefix code.	      *
+* Because the average hit ratio is only 2 (2 hash references per entry),      *
+* evaluating more complex keys (such as twin prime keys) does not worth it!   *
+******************************************************************************/
+static int iGIFHashKeyItem(unsigned int Item)
+{
+  return ((Item >> 12) ^ Item) & GIF_HT_KEY_MASK;
+}
+
+/******************************************************************************
+* Routine to insert a new Item into the HashTable. The data is assumed to be  *
+* new one.								      *
+******************************************************************************/
+static void iGIFInsertHashTable(unsigned int *HTable, unsigned int Key, int Code)
+{
+  int HKey = iGIFHashKeyItem(Key);
+
+  while (GIF_HT_GET_KEY(HTable[HKey]) != 0xFFFFFL) 
+  {
+    HKey = (HKey + 1) & GIF_HT_KEY_MASK;
+  }
+
+  HTable[HKey] = GIF_HT_PUT_KEY(Key) | GIF_HT_PUT_CODE(Code);
+}
+
+/******************************************************************************
+* Routine to test if given Key exists in HashTable and if so returns its code *
+* Returns the Code if key was found, -1 if not.				      *
+******************************************************************************/
+static int iGIFExistsHashTable(unsigned int *HTable, unsigned int Key)
+{
+  int HKey = iGIFHashKeyItem(Key);
+  unsigned int HTKey;
+
+  while ((HTKey = GIF_HT_GET_KEY(HTable[HKey])) != 0xFFFFFL) 
+  {
+    if (Key == HTKey) 
+      return GIF_HT_GET_CODE(HTable[HKey]);
+
+    HKey = (HKey + 1) & GIF_HT_KEY_MASK;
+  }
+
+  return -1;
+}
+
+/******************************************************************************
+*   This routines buffers the given characters until 255 characters are ready *
+* to be output. If Code is equal to -1 the buffer is flushed (EOF).	      *
+*   The buffer is Dumped with first byte as its size, as GIF format requires. *
+******************************************************************************/
+static int iGIFBufferedOutput(imBinFile* handle, unsigned char *Buf, int c)
+{
+  if (c == GIF_FLUSH_OUTPUT) 
+  {
+    /* Flush everything out. */
+    if (Buf[0] != 0)
+      imBinFileWrite(handle, Buf, Buf[0] + 1, 1);
+
+    /* Mark end of compressed data, by an empty block (see GIF doc): */
+    Buf[0] = 0;
+    imBinFileWrite(handle, Buf, 1, 1);
+  }
+  else 
+  {
+    if (Buf[0] == 255) 
+    {
+      /* Dump out this buffer - it is full: */
+      imBinFileWrite(handle, Buf, Buf[0] + 1, 1);
+      Buf[0] = 0;
+    }
+
+    Buf[++Buf[0]] = (unsigned char)c;
+  }
+
+  if (imBinFileError(handle))
+    return IM_ERR_ACCESS;
+
+  return IM_ERR_NONE;
+}
+
+static int iGIFWriteNetscapeApplication(imBinFile* handle, short iterations)
+{
+  /* record type byte */
+  imBinFileWrite(handle, (void*)"!", 1, 1);
+
+  /* block label */
+  imBinFileWrite(handle, (void*)"\xFF", 1, 1);
+
+  /* block size */
+  imBinFileWrite(handle, (void*)"\x0B", 1, 1);
+
+  /* application identifier + athentication code */
+  imBinFileWrite(handle, (void*)"NETSCAPE2.0", 11, 1);
+
+  /* sub block size */
+  imBinFileWrite(handle, (void*)"\x3", 1, 1);
+
+  /* ??? */
+  imBinFileWrite(handle, (void*)"\x1", 1, 1);
+
+  /* iterations */
+  imBinFileWrite(handle, &iterations, 1, 2);
+
+  /* block terminator */
+  imBinFileWrite(handle, (void*)"\0", 1, 1);
+
+  if (imBinFileError(handle))
+    return IM_ERR_ACCESS;
+
+  return IM_ERR_NONE;
+}
+
+/******************************************************************************
+*   The LZ compression output routine:					      *
+*   This routine is responsable for the compression of the bit stream into    *
+* 8 bits (bytes) packets.						      *
+******************************************************************************/
+static int iGIFCompressOutput(iGIFData* igif, imBinFile* handle, int Code)
+{
+  int error = IM_ERR_NONE;
+
+  if (Code == GIF_FLUSH_OUTPUT) 
+  {
+    while (igif->CrntShiftState > 0) 
+    {
+      /* Get Rid of what is left in DWord, and flush it. */
+      error = iGIFBufferedOutput(handle, igif->Buf, igif->CrntShiftDWord & 0xff);
+      igif->CrntShiftDWord >>= 8;
+      igif->CrntShiftState -= 8;
+    }
+    igif->CrntShiftState = 0;			   /* For next time. */
+    error = iGIFBufferedOutput(handle, igif->Buf, GIF_FLUSH_OUTPUT);
+  }
+  else 
+  {
+    igif->CrntShiftDWord |= ((int) Code) << igif->CrntShiftState;
+    igif->CrntShiftState += igif->RunningBits;
+    while (igif->CrntShiftState >= 8) 
+    {
+      /* Dump out full bytes: */
+      error = iGIFBufferedOutput(handle, igif->Buf, igif->CrntShiftDWord & 0xff);
+      igif->CrntShiftDWord >>= 8;
+      igif->CrntShiftState -= 8;
+    }
+  }
+
+  /* If code cannt fit into RunningBits bits, must raise its size. Note */
+  /* however that codes above 4095 are used for special signaling.      */
+  if (igif->RunningCode >= igif->MaxCode1 && Code <= GIF_LZ_MAX_CODE) 
+  {
+    igif->MaxCode1 = 1 << ++igif->RunningBits;
+  }
+
+  return error;
+}
+
+/******************************************************************************
+*   The LZ compression routine:						      *
+*   This version compress the given buffer Line of length LineLen.	      *
+*   This routine can be called few times (one per scan line, for example), in *
+* order the complete the whole image.					      *
+******************************************************************************/
+static int iGIFCompressLine(iGIFData* igif, imBinFile* handle, unsigned char *Line, int LineLen)
+{
+  int i = 0, CrntCode, NewCode;
+  unsigned int NewKey;
+  unsigned char Pixel;
+
+  if (igif->CrntCode == GIF_FIRST_CODE)		  /* Its first time! */
+    CrntCode = Line[i++];
+  else
+    CrntCode = igif->CrntCode;     /* Get last code in compression. */
+
+  while (i < LineLen) 
+  {			    /* Decode LineLen items. */
+    Pixel = Line[i++];		      /* Get next pixel from stream. */
+    /* Form a new unique key to search hash table for the code combines  */
+    /* CrntCode as Prefix string with Pixel as postfix char.	     */
+    NewKey = (((unsigned int) CrntCode) << 8) + Pixel;
+
+    if ((NewCode = iGIFExistsHashTable(igif->HTable, NewKey)) >= 0) 
+    {
+      /* This Key is already there, or the string is old one, so	     */
+      /* simple take new code as our CrntCode:			     */
+      CrntCode = NewCode;
+    }
+    else 
+    {
+      /* Put it in hash table, output the prefix code, and make our    */
+      /* CrntCode equal to Pixel.					     */
+      if (iGIFCompressOutput(igif, handle, CrntCode) != IM_ERR_NONE) 
+        return IM_ERR_ACCESS;
+
+      CrntCode = Pixel;
+
+      /* If however the HashTable if full, we send a clear first and   */
+      /* Clear the hash table.					     */
+      if (igif->RunningCode >= GIF_LZ_MAX_CODE) 
+      {
+        /* Time to do some clearance: */
+        if (iGIFCompressOutput(igif, handle, igif->ClearCode) != IM_ERR_NONE) 
+          return IM_ERR_ACCESS;
+
+        igif->RunningCode = igif->EOFCode + 1;
+        igif->RunningBits = igif->BitsPerPixel + 1;
+        igif->MaxCode1 = 1 << igif->RunningBits;
+        memset(igif->HTable, 0xFF, GIF_HT_SIZE * sizeof(int));
+      }
+      else 
+      {
+        /* Put this unique key with its relative Code in hash table: */
+        iGIFInsertHashTable(igif->HTable, NewKey, igif->RunningCode++);
+      }
+    }
+  }
+
+  /* Preserve the current state of the compression algorithm: */
+  igif->CrntCode = CrntCode;
+
+  return IM_ERR_NONE;
+}
+
+/******************************************************************************
+*   This routines read one gif data block at a time and buffers it internally *
+* so that the decompression routine could access it.			      *
+*   The routine returns the next byte from its internal buffer (or read next  *
+* block in if buffer empty).		      *
+******************************************************************************/
+static int iGIFBufferedInput(imBinFile* handle, unsigned char *Buf, unsigned char *NextByte)
+{
+  if (Buf[0] == 0) 
+  {
+    /* Needs to read the next buffer - this one is empty: */
+    imBinFileRead(handle, Buf, 1, 1);
+    imBinFileRead(handle, &Buf[1], Buf[0], 1);
+
+    if (imBinFileError(handle))
+      return IM_ERR_ACCESS;
+
+    *NextByte = Buf[1];
+    Buf[1] = 2;	   /* We use now the second place as last char read! */
+    Buf[0]--;
+  }
+  else 
+  {
+    *NextByte = Buf[Buf[1]++];
+    Buf[0]--;
+  }
+
+  return IM_ERR_NONE;
+}
+
+/******************************************************************************
+*   The LZ decompression input routine:					      *
+*   This routine is responsable for the decompression of the bit stream from  *
+* 8 bits (bytes) packets, into the real codes.				      *
+******************************************************************************/
+static int iGIFDecompressInput(iGIFData* igif, imBinFile* handle, int *Code)
+{
+  unsigned char NextByte;
+  static unsigned int CodeMasks[] = 
+  {
+    0x0000, 0x0001, 0x0003, 0x0007,
+    0x000f, 0x001f, 0x003f, 0x007f,
+    0x00ff, 0x01ff, 0x03ff, 0x07ff,
+    0x0fff
+  };
+
+  while (igif->CrntShiftState < igif->RunningBits) 
+  {
+    /* Needs to get more bytes from input stream for next code: */
+    if (iGIFBufferedInput(handle, igif->Buf, &NextByte) != IM_ERR_NONE) 
+      return IM_ERR_ACCESS;
+
+    igif->CrntShiftDWord |= ((unsigned int) NextByte) << igif->CrntShiftState;
+    igif->CrntShiftState += 8;
+  }
+
+  *Code = igif->CrntShiftDWord & CodeMasks[igif->RunningBits];
+
+  igif->CrntShiftDWord >>= igif->RunningBits;
+  igif->CrntShiftState -= igif->RunningBits;
+
+  /* If code cannt fit into RunningBits bits, must raise its size. Note */
+  /* however that codes above 4095 are used for special signaling.      */
+  if (++(igif->RunningCode) > igif->MaxCode1 && igif->RunningBits < GIF_LZ_BITS) 
+  {
+    igif->MaxCode1 <<= 1;
+    igif->RunningBits++;
+  }
+
+  return IM_ERR_NONE;
+}
+
+/******************************************************************************
+* Routine to trace the Prefixes linked list until we get a prefix which is    *
+* not code, but a pixel value (less than ClearCode). Returns that pixel value.*
+* If image is defective, we might loop here forever, so we limit the loops to *
+* the maximum possible if image O.k. - LZ_MAX_CODE times.		      *
+******************************************************************************/
+static int iGIFGetPrefixChar(unsigned int *Prefix, int Code, int ClearCode)
+{
+  int i = 0;
+
+  while (Code > ClearCode && i++ <= GIF_LZ_MAX_CODE) 
+    Code = Prefix[Code];
+
+  return Code;
+}
+
+static int iGIFDecompressLine(iGIFData* igif, imBinFile* handle, unsigned char *Line,	int LineLen)
+{
+  int i = 0, j, CrntCode, EOFCode, ClearCode, CrntPrefix, LastCode, StackPtr;
+  unsigned char *Stack, *Suffix;
+  unsigned int *Prefix;
+
+  StackPtr = igif->StackPtr;
+  Prefix = igif->Prefix;
+  Suffix = igif->Suffix;
+  Stack = igif->Stack;
+  EOFCode = igif->EOFCode;
+  ClearCode = igif->ClearCode;
+  LastCode = igif->LastCode;
+
+  if (StackPtr != 0) 
+  {
+    /* Let pop the stack off before continueing to read the gif file: */
+    while (StackPtr != 0 && i < LineLen) 
+      Line[i++] = Stack[--StackPtr];
+  }
+
+  while (i < LineLen) 
+  {			    
+    /* Decode LineLen items. */
+    if (iGIFDecompressInput(igif, handle, &CrntCode))
+      return IM_ERR_ACCESS;
+
+    if (CrntCode == EOFCode) 
+    {
+      /* Note however that usually we will not be here as we will stop */
+      /* decoding as soon as we got all the pixel, or EOF code will    */
+      /* not be read at all, and DGifGetLine/Pixel clean everything.   */
+      if (i != LineLen - 1) 
+        return IM_ERR_ACCESS;
+  
+    i++;
+    }
+    else if (CrntCode == ClearCode) 
+    {
+      /* We need to start over again: */
+      for (j = 0; j <= GIF_LZ_MAX_CODE; j++) 
+        Prefix[j] = GIF_NO_SUCH_CODE;
+
+      igif->RunningCode = igif->EOFCode + 1;
+      igif->RunningBits = igif->BitsPerPixel + 1;
+      igif->MaxCode1 = 1 << igif->RunningBits;
+      LastCode = igif->LastCode = GIF_NO_SUCH_CODE;
+    }
+    else 
+    {
+      /* Its regular code - if in pixel range simply add it to output  */
+      /* stream, otherwise trace to codes linked list until the prefix */
+      /* is in pixel range:					     */
+      if (CrntCode < ClearCode) 
+      {
+        /* This is simple - its pixel scalar, so add it to output:   */
+        Line[i++] = (unsigned char)CrntCode;
+      }
+      else 
+      {
+        /* Its a code to needed to be traced: trace the linked list  */
+        /* until the prefix is a pixel, while pushing the suffix     */
+        /* pixels on our stack. If we done, pop the stack in reverse */
+        /* (thats what stack is good for!) order to output.	     */
+        if (Prefix[CrntCode] == GIF_NO_SUCH_CODE) 
+        {
+          /* Only allowed if CrntCode is exactly the running code: */
+          /* In that case CrntCode = XXXCode, CrntCode or the	     */
+          /* prefix code is last code and the suffix char is	     */
+          /* exactly the prefix of last code!			     */
+          if (CrntCode == igif->RunningCode - 2) 
+          {
+            CrntPrefix = LastCode;
+            Suffix[igif->RunningCode - 2] =
+            Stack[StackPtr++] = (unsigned char)iGIFGetPrefixChar(Prefix, LastCode, ClearCode);
+          }
+          else 
+            return IM_ERR_ACCESS;
+        }
+        else
+          CrntPrefix = CrntCode;
+
+        /* Now (if image is O.K.) we should not get an NO_SUCH_CODE  */
+        /* During the trace. As we might loop forever, in case of    */
+        /* defective image, we count the number of loops we trace    */
+        /* and stop if we got LZ_MAX_CODE. obviously we can not      */
+        /* loop more than that.					     */
+        j = 0;
+        while (j++ <= GIF_LZ_MAX_CODE && CrntPrefix > ClearCode && CrntPrefix <= GIF_LZ_MAX_CODE) 
+        {
+          Stack[StackPtr++] = Suffix[CrntPrefix];
+          CrntPrefix = Prefix[CrntPrefix];
+        }
+
+        if (j >= GIF_LZ_MAX_CODE || CrntPrefix > GIF_LZ_MAX_CODE) 
+            return IM_ERR_ACCESS;
+
+        /* Push the last character on stack: */
+        Stack[StackPtr++] = (unsigned char)CrntPrefix;
+
+        /* Now lets pop all the stack into output: */
+        while (StackPtr != 0 && i < LineLen)
+          Line[i++] = Stack[--StackPtr];
+      }
+
+      if (LastCode != GIF_NO_SUCH_CODE) 
+      {
+        Prefix[igif->RunningCode - 2] = LastCode;
+
+        if (CrntCode == igif->RunningCode - 2) 
+        {
+          /* Only allowed if CrntCode is exactly the running code: */
+          /* In that case CrntCode = XXXCode, CrntCode or the	     */
+          /* prefix code is last code and the suffix char is	     */
+          /* exactly the prefix of last code!			     */
+          Suffix[igif->RunningCode - 2] = (unsigned char)iGIFGetPrefixChar(Prefix, LastCode, ClearCode);
+        }
+        else 
+        {
+          Suffix[igif->RunningCode - 2] = (unsigned char)iGIFGetPrefixChar(Prefix, CrntCode, ClearCode);
+        }
+      }
+    
+      LastCode = CrntCode;
+    }
+  }
+
+  igif->LastCode = LastCode;
+  igif->StackPtr = StackPtr;
+
+  return IM_ERR_NONE;
+}
+
+/*******************************************
+*   Skip sub-blocks until terminator found *
+********************************************/
+static int iGIFSkipSubBlocks(imBinFile* handle)
+{
+  unsigned char byte_value;
+  do
+  {
+    /* reads the number of bytes of the block or the terminator */
+    imBinFileRead(handle, &byte_value, 1, 1);
+
+    if (imBinFileError(handle))
+      return IM_ERR_ACCESS;
+
+    /* jump number of bytes, ignores the contents */
+    if (byte_value) imBinFileSeekOffset(handle, byte_value);
+  }while (byte_value != 0);
+
+  return IM_ERR_NONE;
+}
+
+static int iGIFSkipImage(imBinFile* handle, int *image_count, int *terminate)
+{
+  int found_image = 0;
+  unsigned char byte_value;
+
+  *terminate = 0;
+  do
+  {
+    /* reads the record type byte */
+    byte_value = 0;
+    imBinFileRead(handle, &byte_value, 1, 1);
+
+    switch (byte_value) 
+    {
+	  case ',': /* image description */
+      /* jump 8 bytes */
+      imBinFileSeekOffset(handle, 8);
+
+      /* reads the image information byte */
+      imBinFileRead(handle, &byte_value, 1, 1);
+
+      if (byte_value & 0x80)
+      {
+        int bpp = (byte_value & 0x07) + 1;
+        int num_colors = 1 << bpp;
+
+        /* skip the color table */
+        imBinFileSeekOffset(handle, 3*num_colors);
+      }
+
+      /* jump 1 byte (LZW Min Code) */
+      imBinFileSeekOffset(handle, 1);
+
+      if (imBinFileError(handle))
+        return IM_ERR_ACCESS;
+
+      /* skip sub blocks */
+      if (iGIFSkipSubBlocks(handle) != IM_ERR_NONE)
+        return IM_ERR_ACCESS;
+
+      /* one more image */
+      found_image = 1;
+      (*image_count)++;
+	    break;
+	  case '!': /* extension */
+      /* jump 1 byte (label) */
+      imBinFileSeekOffset(handle, 1);
+
+      /* skip sub blocks */
+      if (iGIFSkipSubBlocks(handle) != IM_ERR_NONE)
+        return IM_ERR_ACCESS;
+	    break;
+	  case ';': /* terminate */
+	  default:  /* probably EOF */
+      *terminate = 1;
+      break;
+	  }
+
+  } while (!(*terminate) && (!found_image));
+
+  if (!found_image && *image_count == 0)
+    return IM_ERR_FORMAT;
+
+  if (imBinFileError(handle))
+    return IM_ERR_ACCESS;
+
+  return IM_ERR_NONE;
+}
+
+static void iGIFReadGraphicsControl(imBinFile* handle, imAttribTable* attrib_table)
+{
+  unsigned char byte_value;
+  unsigned short word_value;
+
+  /* jump 1 bytes (size) */
+  imBinFileSeekOffset(handle, 1);
+
+  /* reads the packed descrition */
+  imBinFileRead(handle, &byte_value, 1, 1);
+  if (imBinFileError(handle))
+    return;
+
+  /* user input */
+  if (byte_value & 0x02)
+    attrib_table->Set("UserInput", IM_BYTE, 1, "\x1");
+
+  /* disposal */
+  if (byte_value & 0x1C)
+  {
+    char* disposal;
+    int disp = (byte_value & 0x1C) >> 2;
+
+    switch (disp)
+    {
+    default:
+      disposal = "UNDEF";
+      break;
+    case 0x01:
+      disposal = "LEAVE";
+      break;
+    case 0x02:
+      disposal = "RBACK";
+      break;
+    case 0x04:
+      disposal = "RPREV";
+      break;
+    }
+
+    attrib_table->Set("Disposal", IM_BYTE, 6, disposal);
+  }
+
+  /* delay time */
+  imBinFileRead(handle, &word_value, 1, 2);
+  if (word_value)
+    attrib_table->Set("Delay", IM_USHORT, 1, &word_value);
+
+  /* transparency color */
+  if (byte_value & 0x01)
+  {
+    imBinFileRead(handle, &byte_value, 1, 1);
+    attrib_table->Set("TransparencyIndex", IM_BYTE, 1, &byte_value);
+  }
+  else
+    imBinFileSeekOffset(handle, 1);
+
+  /* jump 1 bytes (terminator) */
+  imBinFileSeekOffset(handle, 1);
+}
+
+static int iGIFReadApplication(imBinFile* handle, imAttribTable* attrib_table)
+{
+  char identifier[9];
+
+  /* jump 1 byte (size) */
+  imBinFileSeekOffset(handle, 1);
+
+  /* reads the application identifier */
+  imBinFileRead(handle, identifier, 8, 1);
+  if (identifier[7] != 0)
+    identifier[8] = 0;
+
+  if (imBinFileError(handle))
+    return IM_ERR_ACCESS;
+
+  if (imStrEqual(identifier, "NETSCAPE"))
+  {
+    unsigned char authentication[4];
+    /* reads the application authentication code */
+    imBinFileRead(handle, authentication, 3, 1);
+    authentication[3] = 0;
+
+    if (imBinFileError(handle))
+      return IM_ERR_ACCESS;
+
+    if (strcmp((char*)authentication, "2.0") == 0)
+    {
+      unsigned short word_value;
+
+      /* jump 2 bytes (size + 1) */
+      imBinFileSeekOffset(handle, 2);
+
+      /* reads the number of iterations */
+      imBinFileRead(handle, &word_value, 1, 2);
+
+      attrib_table->Set("Iterations", IM_USHORT, 1, &word_value);
+
+      /* jump 1 byte (terminator) */
+      imBinFileSeekOffset(handle, 1);
+
+      if (imBinFileError(handle))
+        return IM_ERR_ACCESS;
+    }
+    else
+    {
+      /* Skip remaining blocks */
+      if (iGIFSkipSubBlocks(handle) != IM_ERR_NONE)
+        return IM_ERR_ACCESS;
+    }
+  }
+  else
+  {
+    /* jump 3 bytes (authentication code) */
+    imBinFileSeekOffset(handle, 3);
+
+    /* Skip remaining blocks */
+    if (iGIFSkipSubBlocks(handle) != IM_ERR_NONE)
+      return IM_ERR_ACCESS;
+  }
+
+  return IM_ERR_NONE;
+}
+
+static int iGIFReadComment(imBinFile* handle, imAttribTable* attrib_table)
+{
+  unsigned char byte_value, buffer[255*100] = "", *buffer_ptr;
+  int size = 0;
+
+  buffer_ptr = &buffer[0];
+
+  do
+  {
+    /* reads the number of bytes of the block or the terminator */
+    imBinFileRead(handle, &byte_value, 1, 1);
+
+    if (imBinFileError(handle))
+      return IM_ERR_ACCESS;
+
+    /* reads data */
+    if (byte_value)
+    {
+      imBinFileRead(handle, buffer_ptr, byte_value, 1);
+
+      if (buffer_ptr[byte_value-1] == 0)
+      {
+        size += byte_value-1;
+        buffer_ptr += byte_value-1;
+      }
+      else
+      {
+        size += byte_value;
+        buffer_ptr += byte_value;
+      }
+    }
+
+  }while (byte_value != 0);
+
+  if (buffer[0] != 0)
+    attrib_table->Set("Description", IM_BYTE, size, buffer);
+
+  return IM_ERR_NONE;
+}
+
+static int iGIFReadExtension(imBinFile* handle, imAttribTable* attrib_table)
+{
+  unsigned char byte_value;
+
+  /* read block label */
+  imBinFileRead(handle, &byte_value, 1, 1);
+
+  if (byte_value == 0xF9)
+  {
+    /* Graphics Control Extension */
+    iGIFReadGraphicsControl(handle, attrib_table);
+  }
+  else if (byte_value == 0xFE)
+  {
+    /* Comment Extension */
+    if (iGIFReadComment(handle, attrib_table) != IM_ERR_NONE)
+      return IM_ERR_ACCESS;
+  }
+  else if (byte_value == 0xFF)
+  {
+    /* Application Extension */
+    if (iGIFReadApplication(handle, attrib_table) != IM_ERR_NONE)
+      return IM_ERR_ACCESS;
+  }
+  else
+  {
+    /* skip sub blocks */
+    if (iGIFSkipSubBlocks(handle) != IM_ERR_NONE)
+      return IM_ERR_ACCESS;
+  }
+
+  if (imBinFileError(handle))
+    return IM_ERR_ACCESS;
+
+  return IM_ERR_NONE;
+}
+
+static int iGIFWriteComment(imBinFile* handle, unsigned char *buffer, int size)
+{
+  unsigned char byte_value;
+
+  /* record type byte */
+  imBinFileWrite(handle, (void*)"!", 1, 1);
+
+  /* block label */
+  imBinFileWrite(handle, (void*)"\xFE", 1, 1);
+
+  while (size > 0)
+  {
+    if (size > 255)
+      byte_value = 255;
+    else
+      byte_value = (unsigned char)size;
+
+    /* sub block size */
+    imBinFileWrite(handle, &byte_value, 1, 1);
+
+    /* sub block data */
+    imBinFileWrite(handle, buffer, byte_value, 1);
+
+    buffer += byte_value;
+    size -= byte_value;
+
+    if (imBinFileError(handle))
+      return IM_ERR_ACCESS;
+  }
+
+  /* block terminator */
+  imBinFileWrite(handle, (void*)"\0", 1, 1);
+
+  return IM_ERR_NONE;
+}
+
+static int iGIFWriteGraphicsControl(imBinFile* handle, imAttribTable* attrib_table)
+{
+  const void *attrib_user_input, *attrib_disposal, *attrib_delay, *attrib_transparency;
+  unsigned char byte_value;
+
+  attrib_user_input = attrib_table->Get("UserInput");
+  attrib_disposal = attrib_table->Get("Disposal");
+  attrib_delay = attrib_table->Get("Delay");
+  attrib_transparency = attrib_table->Get("TransparencyIndex");
+
+  /* Writes the Graphics Control Extension */
+  if (attrib_user_input || attrib_disposal || attrib_delay || attrib_transparency)
+  {
+    unsigned short word_value;
+
+    /* record type byte */
+    imBinFileWrite(handle, (void*)"!", 1, 1);
+
+    /* block label */
+    imBinFileWrite(handle, (void*)"\xF9", 1, 1);
+
+    /* block size */
+    imBinFileWrite(handle, (void*)"\x04", 1, 1);
+
+    byte_value = 0;
+
+    /* user input flag */
+    if (attrib_user_input && *(unsigned char*)attrib_user_input == 1)
+      byte_value |= 0x02;
+
+    /* transparency flag */
+    if (attrib_transparency)
+      byte_value |= 0x01;
+
+    /* disposal flag */
+    if (attrib_disposal)
+    {
+      int disp = 0;
+      if (imStrEqual((char*)attrib_disposal, "LEAVE"))
+        disp = 0x01;
+      else if (imStrEqual((char*)attrib_disposal, "RBACK"))
+        disp = 0x02;
+      else if (imStrEqual((char*)attrib_disposal, "RPREV"))
+        disp = 0x04;
+
+      disp = disp << 2;
+      byte_value |= disp;
+    }
+
+    /* packed */
+    imBinFileWrite(handle, &byte_value, 1, 1);
+
+    /* delay time */
+    if (attrib_delay)
+      word_value = *(unsigned short*)attrib_delay;
+    else
+      word_value = 0;
+
+    imBinFileWrite(handle, &word_value, 1, 2);
+
+    /* transparency color */
+    if (attrib_transparency)
+    {
+      byte_value = *(unsigned char*)attrib_transparency;
+      imBinFileWrite(handle, &byte_value, 1, 1);
+    }
+    else
+      imBinFileWrite(handle, (void*)"\0", 1, 1);
+
+    /* terminator */
+    imBinFileWrite(handle, (void*)"\0", 1, 1);
+
+    if (imBinFileError(handle))
+      return IM_ERR_ACCESS;
+  }
+
+  return IM_ERR_NONE;
+}
+
+static const char* iGIFCompTable[1] = 
+{
+  "LZW"
+};
+
+class imFormatGIF: public imFormat
+{
+  imBinFile* handle;
+  iGIFData gif_data;
+
+  int GIFReadImageInfo();
+  int GIFWriteImageInfo();
+
+public:
+  imFormatGIF()
+    :imFormat("GIF", 
+              "Graphics Interchange Format", 
+              "*.gif;", 
+              iGIFCompTable, 
+              1, 
+              1)
+    {}
+  ~imFormatGIF() {}
+
+  int Open(const char* file_name);
+  int New(const char* file_name);
+  void Close();
+  void* Handle(int index);
+  int ReadImageInfo(int index);
+  int ReadImageData(void* data);
+  int WriteImageInfo();
+  int WriteImageData(void* data);
+  int CanWrite(const char* compression, int color_mode, int data_type) const;
+};
+
+void imFormatRegisterGIF(void)
+{
+  imFormatRegister(new imFormatGIF());
+}
+
+int imFormatGIF::Open(const char* file_name)
+{
+  this->handle = imBinFileOpen(file_name);
+  if (this->handle == NULL)
+    return IM_ERR_OPEN;
+
+  imBinFileByteOrder(handle, IM_LITTLEENDIAN); 
+
+  unsigned char sig[4];
+  if (!imBinFileRead(this->handle, sig, 3, 1))
+  {
+    imBinFileClose(handle);
+    return IM_ERR_ACCESS;
+  }
+
+  sig[3] = 0;
+  if (!imStrEqual((char*)sig, GIF_STAMP))
+  {
+    imBinFileClose(handle);
+    return IM_ERR_FORMAT;
+  }
+
+  /* ignore version */
+  imBinFileSeekOffset(handle, 3);
+
+  strcpy(this->compression, "LZW");
+
+  /* reads screen width and screen height */
+  imushort word_value;
+  imBinFileRead(handle, &word_value, 1, 2);
+  gif_data.screen_width = word_value;
+
+  imBinFileRead(handle, &word_value, 1, 2);
+  gif_data.screen_height = word_value;
+
+  /* reads color table information byte */
+  imbyte byte_value;
+  imBinFileRead(handle, &byte_value, 1, 1);
+
+  /* jump 2 bytes (bgcolor + aspect ratio) */
+  imBinFileSeekOffset(handle, 2);
+
+  /* global color table, if exists */
+  if (byte_value & 0x80)
+  {
+    int bpp = (byte_value & 0x07) + 1;
+    gif_data.global_num_colors = 1 << bpp;
+
+    /* reads the color palette */
+    imBinFileRead(handle, gif_data.global_colors, gif_data.global_num_colors * 3, 1);
+  }
+
+  if (imBinFileError(handle))
+  {
+    imBinFileClose(handle);
+    return IM_ERR_ACCESS;
+  }
+
+  /* count number of images */
+  int error, terminate;
+  this->image_count = 0;
+  do
+  {
+    // store each offset before counting images
+    gif_data.start_offset[this->image_count] = imBinFileTell(handle);
+    error = iGIFSkipImage(handle, &this->image_count, &terminate);
+  } while (!terminate && error == IM_ERR_NONE);
+
+  if (this->image_count == 0 || error != IM_ERR_NONE)
+  {
+    imBinFileClose(handle);
+    return error;
+  }
+
+  return IM_ERR_NONE;
+}
+
+int imFormatGIF::New(const char* file_name)
+{
+  this->handle = imBinFileNew(file_name);
+  if (this->handle == NULL)
+    return IM_ERR_OPEN;
+
+  imBinFileByteOrder(handle, IM_LITTLEENDIAN); 
+
+  /* writes the GIF STAMP and version - header */
+  imBinFileWrite(handle, (void*)GIF_STAMP, 3, 1);   /* identifier */
+  imBinFileWrite(handle, (void*)GIF_VERSION, 3, 1); /* format version */
+
+  // File header will be written at the first image
+
+  /* tests if everything was ok */
+  if (imBinFileError(handle))
+  {
+    imBinFileClose(this->handle);
+    return IM_ERR_ACCESS;
+  }
+
+  strcpy(this->compression, "LZW");
+  
+  return IM_ERR_NONE;
+}
+
+void imFormatGIF::Close()
+{
+  if (this->is_new && !imBinFileError(this->handle))
+    imBinFileWrite(this->handle, (void*)";", 1, 1);
+
+  imBinFileClose(this->handle);
+}
+
+void* imFormatGIF::Handle(int index)
+{
+  if (index == 0)
+    return (void*)this->handle;
+  else
+    return NULL;
+}
+
+int imFormatGIF::GIFReadImageInfo()
+{
+  imbyte byte_value;
+  imushort word_value;
+  int int_value;
+
+  imAttribTable* attrib_table = AttribTable();
+
+  /* reads the image left position */
+  imBinFileRead(handle, &word_value, 1, 2);
+  if (word_value)
+    attrib_table->Set("XScreen", IM_USHORT, 1, &word_value);
+
+  /* reads the image top position */
+  imBinFileRead(handle, &word_value, 1, 2);
+  if (word_value)
+    attrib_table->Set("YScreen", IM_USHORT, 1, &word_value);
+
+  /* reads the image width */
+  imBinFileRead(handle, &word_value, 1, 2);
+  this->width = word_value;
+
+  /* reads the image height */
+  imBinFileRead(handle, &word_value, 1, 2);
+  this->height = word_value;
+
+  /* reads the image information byte */
+  imBinFileRead(handle, &byte_value, 1, 1);
+
+  gif_data.interlaced = (byte_value & 0x40)? 1: 0;
+  if (gif_data.interlaced)
+  {
+    int_value = 1;
+    attrib_table->Set("Interlaced", IM_INT, 1, &int_value);
+  }
+
+  this->file_color_mode = IM_MAP;
+  this->file_data_type = IM_BYTE;
+
+  /* local color table */
+  int num_colors;
+  unsigned char *colors;
+  unsigned char local_colors[256 * 3];
+
+  if (byte_value & 0x80)
+  {
+    int bpp = (byte_value & 0x07) + 1;
+    num_colors = 1 << bpp;
+    colors = local_colors;
+
+    /* reads the color table */
+    imBinFileRead(handle, local_colors, num_colors * 3, 1);
+  }
+  else if (gif_data.global_num_colors)
+  {
+    colors = gif_data.global_colors;
+    num_colors = gif_data.global_num_colors;
+  }
+  else
+    return IM_ERR_FORMAT;
+
+  long palette[256];
+  for (int c = 0; c < num_colors; c++)
+  {
+    palette[c] = imColorEncode(colors[c*3],
+                               colors[c*3+1],
+                               colors[c*3+2]);
+  }
+
+  imFileSetPalette(this, palette, num_colors);
+
+  if (imBinFileError(handle))
+    return IM_ERR_ACCESS;
+
+  this->file_color_mode |= IM_TOPDOWN;
+
+  return IM_ERR_NONE;
+}
+
+int imFormatGIF::GIFWriteImageInfo()
+{
+  this->file_data_type = IM_BYTE;
+  this->file_color_mode = imColorModeSpace(this->user_color_mode);
+  this->file_color_mode |= IM_TOPDOWN;
+
+  imAttribTable* attrib_table = AttribTable();
+  const void* attrib = attrib_table->Get("Interlaced");
+  if (attrib)
+    gif_data.interlaced = *(int*)attrib;
+
+  imBinFileWrite(handle, (void*)",", 1, 1);  /* Image separator character. */
+
+  imushort word_value;
+
+  attrib = attrib_table->Get("XScreen");
+  if (attrib)
+    word_value = *(unsigned short*)attrib;
+  else
+    word_value = 0;
+  imBinFileWrite(handle, &word_value, 1, 2); /* image left */
+
+  attrib = attrib_table->Get("YScreen");
+  if (attrib)
+    word_value = *(unsigned short*)attrib;
+  else
+    word_value = 0;
+  imBinFileWrite(handle, &word_value, 1, 2); /* image top */
+
+  word_value = (unsigned short)this->width;
+  imBinFileWrite(handle, &word_value, 1, 2); /* image width */
+  word_value = (unsigned short)this->height;
+  imBinFileWrite(handle, &word_value, 1, 2); /* image height */
+
+  /* local color table */
+  imbyte byte_value = 0x80;
+  if (gif_data.interlaced)
+    byte_value |= 0x40;
+
+  int num_colors = 256;
+  if (imColorModeSpace(this->user_color_mode) == IM_MAP)
+  {
+    int bpp = 0, c = this->palette_count-1;
+    while (c) {c = c >> 1;bpp++;} 
+    byte_value |= (bpp-1); 
+    num_colors = 1 << bpp;
+  }
+  else
+    byte_value |= 0x07; /* 8 bits = 256 grays */
+
+  imBinFileWrite(handle, &byte_value, 1, 1); /* image information */
+
+  /* write color table */
+  unsigned char local_colors[256*3];
+  for (int c = 0; c < num_colors; c++) // write all data, even not used colors
+  {
+    unsigned char r, g, b;
+    imColorDecode(&r, &g, &b, this->palette[c]);
+    local_colors[c*3] = r;
+    local_colors[c*3+1] = g;
+    local_colors[c*3+2] = b;
+  }
+  imBinFileWrite(handle, local_colors, num_colors*3, 1);
+
+  if (imBinFileError(handle))
+    return IM_ERR_ACCESS;
+
+  return IM_ERR_NONE;
+}
+
+int imFormatGIF::ReadImageInfo(int index)
+{
+  imAttribTable* attrib_table = AttribTable();
+  attrib_table->RemoveAll();
+
+  if (gif_data.screen_width) 
+  {
+    imushort word_value = (imushort)gif_data.screen_width;
+    attrib_table->Set("ScreenWidth", IM_USHORT, 1, &word_value);
+  }
+
+  if (gif_data.screen_height) 
+  {
+    imushort word_value = (imushort)gif_data.screen_height;
+    attrib_table->Set("ScreenHeight", IM_USHORT, 1, &word_value);
+  }
+
+  /* jump to start offset of the image */
+  imBinFileSeekTo(handle, gif_data.start_offset[index]);
+
+  int found_image = 0;
+  imbyte byte_value;
+
+  int terminate = 0;
+  do
+  {
+    /* reads the record type byte */
+    byte_value = 0;
+    imBinFileRead(handle, &byte_value, 1, 1);
+
+    switch (byte_value) 
+    {
+	  case '!': /* 0x21 extension (appears before the image) */
+      if (iGIFReadExtension(handle, attrib_table) != IM_ERR_NONE)
+        return IM_ERR_ACCESS;
+	    break;
+	  case ',': /* 0x2C image description and color table */
+      if (GIFReadImageInfo() != IM_ERR_NONE)
+        return IM_ERR_ACCESS;
+
+      /* we will read only this image for now, so break the loop */
+      found_image = 1;
+	    break;
+	  case ';': /* if terminate before find image return error */
+	  default:
+      terminate = 1;
+      break;
+	  }
+  } while (!terminate && !found_image);
+
+  if (!found_image)
+    return IM_ERR_ACCESS;
+
+  if (imBinFileError(handle))
+    return IM_ERR_ACCESS;
+
+  /* reads the LZW Min code byte */
+  imBinFileRead(handle, &byte_value, 1, 1);
+
+  /* now initialize the compression control data */
+
+  gif_data.BitsPerPixel = byte_value;
+  gif_data.ClearCode = (1 << byte_value);
+  gif_data.EOFCode = gif_data.ClearCode + 1;
+  gif_data.RunningCode = gif_data.EOFCode + 1;
+  gif_data.RunningBits = byte_value + 1;	 /* Number of bits per code. */
+  gif_data.MaxCode1 = 1 << gif_data.RunningBits;     /* Max. code + 1. */
+  gif_data.StackPtr = 0;		    /* No pixels on the pixel stack. */
+  gif_data.LastCode = GIF_NO_SUCH_CODE;
+  gif_data.CrntShiftState = 0;	/* No information in CrntShiftDWord. */
+  gif_data.CrntShiftDWord = 0;
+  gif_data.Buf[0] = 0;			      /* Input Buffer empty. */
+
+  for (int i = 0; i <= GIF_LZ_MAX_CODE; i++) 
+    gif_data.Prefix[i] = GIF_NO_SUCH_CODE;
+
+  gif_data.step = 0;
+
+  return IM_ERR_NONE;
+}
+
+int imFormatGIF::WriteImageInfo()
+{
+  this->file_color_mode = imColorModeSpace(this->user_color_mode);
+  this->file_color_mode |= IM_TOPDOWN;
+  this->file_data_type = this->user_data_type;
+
+  imAttribTable* attrib_table = AttribTable();
+  const void* attrib_data;
+  int attrib_size;
+
+  if (this->image_count == 0)
+  {
+    imushort word_value;
+
+    // write file header
+
+    /* logical screen descriptor */
+    attrib_data = attrib_table->Get("ScreenWidth");
+    if (attrib_data) word_value = *(imushort*)attrib_data;
+    else             word_value = (imushort)this->width;
+    imBinFileWrite(handle, &word_value, 1, 2);
+
+    attrib_data = attrib_table->Get("ScreenHeight");
+    if (attrib_data) word_value = *(imushort*)attrib_data;
+    else             word_value = (imushort)this->height;
+    imBinFileWrite(handle, &word_value, 1, 2);
+
+    imbyte byte_value = 0;  /* no global color table, 0 colors */
+    imBinFileWrite(handle, &byte_value, 1, 1); /* screen information */
+    imBinFileWrite(handle, (void*)"\0\0", 2, 1);  /* (bgcolor + aspect ratio) */
+  }
+
+  attrib_data = attrib_table->Get("Description", NULL, &attrib_size);
+  if (attrib_data)
+  {
+    if (iGIFWriteComment(handle, (imbyte*)attrib_data, attrib_size) != IM_ERR_NONE)
+      return IM_ERR_ACCESS;
+  }
+
+  attrib_data = attrib_table->Get("Iterations");
+  if (attrib_data)
+  {
+    if (iGIFWriteNetscapeApplication(handle, *(short*)attrib_data) != IM_ERR_NONE)
+      return IM_ERR_ACCESS;
+  }
+
+  if (iGIFWriteGraphicsControl(handle, attrib_table) != IM_ERR_NONE)
+    return IM_ERR_ACCESS;
+
+  if (GIFWriteImageInfo() != IM_ERR_NONE)
+    return IM_ERR_ACCESS;
+
+  /* initializes the hash table */
+  memset(gif_data.HTable, 0xFF, GIF_HT_SIZE * sizeof(int));
+
+  /* initializes compression data */
+
+  imbyte byte_value = 8;
+  imBinFileWrite(handle, &byte_value, 1, 1); /* Write the Code size to file. */
+
+  gif_data.Buf[0] = 0;			  /* Nothing was output yet. */
+  gif_data.BitsPerPixel = 8;
+  gif_data.ClearCode = (1 << 8);
+  gif_data.EOFCode = gif_data.ClearCode + 1;
+  gif_data.RunningBits = 8 + 1;	 /* Number of bits per code. */
+  gif_data.MaxCode1 = 1 << gif_data.RunningBits;	   /* Max. code + 1. */
+  gif_data.CrntCode = GIF_FIRST_CODE;	   /* Signal that this is first one! */
+  gif_data.CrntShiftState = 0;      /* No information in CrntShiftDWord. */
+  gif_data.CrntShiftDWord = 0;
+
+  gif_data.RunningCode = gif_data.EOFCode + 1;
+
+  if (imBinFileError(handle))
+    return IM_ERR_ACCESS;
+
+  gif_data.step = 0;          /* interlaced step */
+
+  return iGIFCompressOutput(&gif_data, handle, gif_data.ClearCode);
+}
+
+int imFormatGIF::ReadImageData(void* data)
+{
+  imCounterTotal(this->counter, this->height, "Reading GIF...");
+
+  int row = 0, error;
+  for (int i = 0; i < this->height; i++)
+  {
+    error = iGIFDecompressLine(&gif_data, handle, (imbyte*)this->line_buffer, this->width);
+    if (error != IM_ERR_NONE)
+      return IM_ERR_ACCESS;
+
+    imFileLineBufferRead(this, data, row, 0);
+
+    if (!imCounterInc(this->counter))
+      return IM_ERR_COUNTER;
+
+	  if (gif_data.interlaced)
+	  {
+      row += InterlacedJumps[gif_data.step];
+
+      if (row > this->height-1)
+      {
+        gif_data.step++;
+        row = InterlacedOffset[gif_data.step];
+      }
+	  }
+	  else
+      row++;
+  }
+
+  /* Skip remaining empty blocks of the image data */
+  if (iGIFSkipSubBlocks(handle) != IM_ERR_NONE)
+    return IM_ERR_ACCESS;
+
+  return IM_ERR_NONE;
+}
+
+int imFormatGIF::WriteImageData(void* data)
+{
+  imCounterTotal(this->counter, this->height, "Writing GIF...");
+
+  int row = 0, error;
+  for (int i = 0; i < this->height; i++)
+  {
+    imFileLineBufferWrite(this, data, row, 0);
+
+    error = iGIFCompressLine(&gif_data, handle, (imbyte*)this->line_buffer, this->width);
+
+    if (error != IM_ERR_NONE)
+      return IM_ERR_ACCESS;
+
+    if (!imCounterInc(this->counter))
+      return IM_ERR_COUNTER;
+
+	  if (gif_data.interlaced)
+	  {
+      row += InterlacedJumps[gif_data.step];
+
+      if (row > this->height-1)
+      {
+        gif_data.step++;
+        row = InterlacedOffset[gif_data.step];
+      }
+	  }
+	  else
+      row++;
+  }
+
+  /* writes the end picture code */
+  iGIFCompressOutput(&gif_data, handle, gif_data.CrntCode);
+  iGIFCompressOutput(&gif_data, handle, gif_data.EOFCode);
+  iGIFCompressOutput(&gif_data, handle, GIF_FLUSH_OUTPUT);
+
+  if (imBinFileError(handle))
+    return IM_ERR_ACCESS;
+
+  this->image_count++;
+  return IM_ERR_NONE;
+}
+
+int imFormatGIF::CanWrite(const char* compression, int color_mode, int data_type) const
+{
+  int color_space = imColorModeSpace(color_mode);
+
+  if (color_space != IM_MAP && color_space != IM_GRAY && color_space != IM_BINARY)
+    return IM_ERR_DATA;                       
+                                              
+  if (data_type != IM_BYTE)
+    return IM_ERR_DATA;
+
+  if (!compression || compression[0] == 0)
+    return IM_ERR_NONE;
+
+  if (!imStrEqual(compression, "LZW"))
+    return IM_ERR_COMPRESS;
+
+  return IM_ERR_NONE;
+}
+