dgif_lib.c

支持各种栅格图像和矢量图像读取的库

	GifFile->Image.ColorMap = MakeMapObject(1 << BitsPerPixel, NULL);
    
	/* Get the image local color map: */
	for (i = 0; i < GifFile->Image.ColorMap->ColorCount; i++) {
	    if (READ(GifFile,Buf, 3) != 3) {
		_GifError = D_GIF_ERR_READ_FAILED;
		return GIF_ERROR;
	    }
	    GifFile->Image.ColorMap->Colors[i].Red = Buf[0];
	    GifFile->Image.ColorMap->Colors[i].Green = Buf[1];
	    GifFile->Image.ColorMap->Colors[i].Blue = Buf[2];
	}
    }

    if (GifFile->SavedImages) {
        if ((GifFile->SavedImages = (SavedImage *)realloc(GifFile->SavedImages,
                                                          sizeof(SavedImage) * (GifFile->ImageCount + 1))) == NULL) {
            _GifError = D_GIF_ERR_NOT_ENOUGH_MEM;
            return GIF_ERROR;
        }
    } else {
        if ((GifFile->SavedImages =
             (SavedImage *)malloc(sizeof(SavedImage))) == NULL) {
            _GifError = D_GIF_ERR_NOT_ENOUGH_MEM;
            return GIF_ERROR;
        }
    }

    sp = &GifFile->SavedImages[GifFile->ImageCount];
    memcpy(&sp->ImageDesc, &GifFile->Image, sizeof(GifImageDesc));
    if (GifFile->Image.ColorMap != NULL) {
        sp->ImageDesc.ColorMap = MakeMapObject( 
            GifFile->Image.ColorMap->ColorCount, 
            GifFile->Image.ColorMap->Colors );
    }
    sp->RasterBits = (char *)NULL;
    sp->ExtensionBlockCount = 0;
    sp->ExtensionBlocks = (ExtensionBlock *)NULL;

    GifFile->ImageCount++;

    Private->PixelCount = (long) GifFile->Image.Width *
        (long) GifFile->Image.Height;

    DGifSetupDecompress(GifFile);  /* Reset decompress algorithm parameters. */

    return GIF_OK;
}

/******************************************************************************
*  Get one full scanned line (Line) of length LineLen from GIF file.	      *
******************************************************************************/
int DGifGetLine(GifFileType *GifFile, GifPixelType *Line, int LineLen)
{
    GifByteType *Dummy;
    GifFilePrivateType *Private = (GifFilePrivateType *) GifFile->Private;

    if (!IS_READABLE(Private)) {
	/* This file was NOT open for reading: */
	_GifError = D_GIF_ERR_NOT_READABLE;
	return GIF_ERROR;
    }

    if (!LineLen) LineLen = GifFile->Image.Width;

#if defined(__MSDOS__) || defined(__GNUC__)
    if ((Private->PixelCount -= LineLen) > 0xffff0000UL) {
#else
    if ((Private->PixelCount -= LineLen) > 0xffff0000) {
#endif /* __MSDOS__ */
	_GifError = D_GIF_ERR_DATA_TOO_BIG;
	return GIF_ERROR;
    }

    if (DGifDecompressLine(GifFile, Line, LineLen) == GIF_OK) {
	if (Private->PixelCount == 0) {
	    /* We probably would not be called any more, so lets clean 	     */
	    /* everything before we return: need to flush out all rest of    */
	    /* image until empty block (size 0) detected. We use GetCodeNext.*/
	    do if (DGifGetCodeNext(GifFile, &Dummy) == GIF_ERROR)
		return GIF_ERROR;
	    while (Dummy != NULL);
	}
	return GIF_OK;
    }
    else
	return GIF_ERROR;
}

/******************************************************************************
* Put one pixel (Pixel) into GIF file.					      *
******************************************************************************/
int DGifGetPixel(GifFileType *GifFile, GifPixelType Pixel)
{
    GifByteType *Dummy;
    GifFilePrivateType *Private = (GifFilePrivateType *) GifFile->Private;

    if (!IS_READABLE(Private)) {
	/* This file was NOT open for reading: */
	_GifError = D_GIF_ERR_NOT_READABLE;
	return GIF_ERROR;
    }

#if defined(__MSDOS__) || defined(__GNUC__)
    if (--Private->PixelCount > 0xffff0000UL)
#else
    if (--Private->PixelCount > 0xffff0000)
#endif /* __MSDOS__ */
    {
	_GifError = D_GIF_ERR_DATA_TOO_BIG;
	return GIF_ERROR;
    }

    if (DGifDecompressLine(GifFile, &Pixel, 1) == GIF_OK) {
	if (Private->PixelCount == 0) {
	    /* We probably would not be called any more, so lets clean 	     */
	    /* everything before we return: need to flush out all rest of    */
	    /* image until empty block (size 0) detected. We use GetCodeNext.*/
	    do if (DGifGetCodeNext(GifFile, &Dummy) == GIF_ERROR)
		return GIF_ERROR;
	    while (Dummy != NULL);
	}
	return GIF_OK;
    }
    else
	return GIF_ERROR;
}

/******************************************************************************
*   Get an extension block (see GIF manual) from gif file. This routine only  *
* returns the first data block, and DGifGetExtensionNext shouldbe called      *
* after this one until NULL extension is returned.			      *
*   The Extension should NOT be freed by the user (not dynamically allocated).*
*   Note it is assumed the Extension desc. header ('!') has been read.	      *
******************************************************************************/
int DGifGetExtension(GifFileType *GifFile, int *ExtCode,
						    GifByteType **Extension)
{
    GifByteType Buf;
    GifFilePrivateType *Private = (GifFilePrivateType *) GifFile->Private;

    if (!IS_READABLE(Private)) {
	/* This file was NOT open for reading: */
	_GifError = D_GIF_ERR_NOT_READABLE;
	return GIF_ERROR;
    }

    if (READ(GifFile,&Buf, 1) != 1) {
	_GifError = D_GIF_ERR_READ_FAILED;
	return GIF_ERROR;
    }
    *ExtCode = Buf;

    return DGifGetExtensionNext(GifFile, Extension);
}

/******************************************************************************
*   Get a following extension block (see GIF manual) from gif file. This      *
* routine sould be called until NULL Extension is returned.		      *
*   The Extension should NOT be freed by the user (not dynamically allocated).*
******************************************************************************/
int DGifGetExtensionNext(GifFileType *GifFile, GifByteType **Extension)
{
    GifByteType Buf;
    GifFilePrivateType *Private = (GifFilePrivateType *) GifFile->Private;

    if (READ(GifFile,&Buf, 1) != 1) {
	_GifError = D_GIF_ERR_READ_FAILED;
	return GIF_ERROR;
    }
    if (Buf > 0) {
	*Extension = Private->Buf;           /* Use private unused buffer. */
	(*Extension)[0] = Buf;  /* Pascal strings notation (pos. 0 is len.). */
	if (READ(GifFile,&((*Extension)[1]), Buf) != Buf) {
	    _GifError = D_GIF_ERR_READ_FAILED;
	    return GIF_ERROR;
	}
    }
    else
	*Extension = NULL;

    return GIF_OK;
}

/******************************************************************************
*   This routine should be called last, to close the GIF file.		      *
******************************************************************************/
int DGifCloseFile(GifFileType *GifFile)
{
    GifFilePrivateType *Private;
    FILE *File;

    if (GifFile == NULL) return GIF_ERROR;

    Private = (GifFilePrivateType *) GifFile->Private;

    if (!IS_READABLE(Private)) {
	/* This file was NOT open for reading: */
	_GifError = D_GIF_ERR_NOT_READABLE;
	return GIF_ERROR;
    }

    File = Private->File;

    if (GifFile->Image.ColorMap)
	FreeMapObject(GifFile->Image.ColorMap);
    if (GifFile->SColorMap)
	FreeMapObject(GifFile->SColorMap);
    if (Private)
	free((char *) Private);
    if (GifFile->SavedImages)
	FreeSavedImages(GifFile);
    free(GifFile);

    if ( File && (fclose(File) != 0)) {
	  _GifError = D_GIF_ERR_CLOSE_FAILED;
	  return GIF_ERROR;
    }
    return GIF_OK;
}

/******************************************************************************
*   Get 2 bytes (word) from the given file:				      *
******************************************************************************/
static int DGifGetWord(GifFileType *GifFile, int *Word)
{
    unsigned char c[2];

    if (READ(GifFile,c, 2) != 2) {
	_GifError = D_GIF_ERR_READ_FAILED;
	return GIF_ERROR;
    }

    *Word = (((unsigned int) c[1]) << 8) + c[0];
    return GIF_OK;
}

/******************************************************************************
*   Get the image code in compressed form.  his routine can be called if the  *
* information needed to be piped out as is. Obviously this is much faster     *
* than decoding and encoding again. This routine should be followed by calls  *
* to DGifGetCodeNext, until NULL block is returned.			      *
*   The block should NOT be freed by the user (not dynamically allocated).    *
******************************************************************************/
int DGifGetCode(GifFileType *GifFile, int *CodeSize, GifByteType **CodeBlock)
{
    GifFilePrivateType *Private = (GifFilePrivateType *) GifFile->Private;

    if (!IS_READABLE(Private)) {
	/* This file was NOT open for reading: */
	_GifError = D_GIF_ERR_NOT_READABLE;
	return GIF_ERROR;
    }

    *CodeSize = Private->BitsPerPixel;

    return DGifGetCodeNext(GifFile, CodeBlock);
}

/******************************************************************************
*   Continue to get the image code in compressed form. This routine should be *
* called until NULL block is returned.					      *
*   The block should NOT be freed by the user (not dynamically allocated).    *
******************************************************************************/
int DGifGetCodeNext(GifFileType *GifFile, GifByteType **CodeBlock)
{
    GifByteType Buf;
    GifFilePrivateType *Private = (GifFilePrivateType *) GifFile->Private;

    if (READ(GifFile,&Buf, 1) != 1) {
	_GifError = D_GIF_ERR_READ_FAILED;
	return GIF_ERROR;
    }

    if (Buf > 0) {
	*CodeBlock = Private->Buf;	       /* Use private unused buffer. */
	(*CodeBlock)[0] = Buf;  /* Pascal strings notation (pos. 0 is len.). */
	if (READ(GifFile,&((*CodeBlock)[1]), Buf) != Buf) {
	    _GifError = D_GIF_ERR_READ_FAILED;
	    return GIF_ERROR;
	}
    }
    else {
	*CodeBlock = NULL;
	Private->Buf[0] = 0;		   /* Make sure the buffer is empty! */
	Private->PixelCount = 0;   /* And local info. indicate image read. */
    }

    return GIF_OK;
}

/******************************************************************************
*   Setup the LZ decompression for this image:				      *
******************************************************************************/
static int DGifSetupDecompress(GifFileType *GifFile)
{
    int i, BitsPerPixel;
    GifByteType CodeSize;
    unsigned int *Prefix;
    GifFilePrivateType *Private = (GifFilePrivateType *) GifFile->Private;

    READ(GifFile,&CodeSize, 1);    /* Read Code size from file. */
    BitsPerPixel = CodeSize;

    Private->Buf[0] = 0;			      /* Input Buffer empty. */
    Private->BitsPerPixel = BitsPerPixel;
    Private->ClearCode = (1 << BitsPerPixel);
    Private->EOFCode = Private->ClearCode + 1;
    Private->RunningCode = Private->EOFCode + 1;
    Private->RunningBits = BitsPerPixel + 1;	 /* Number of bits per code. */
    Private->MaxCode1 = 1 << Private->RunningBits;     /* Max. code + 1. */
    Private->StackPtr = 0;		    /* No pixels on the pixel stack. */
    Private->LastCode = NO_SUCH_CODE;
    Private->CrntShiftState = 0;	/* No information in CrntShiftDWord. */
    Private->CrntShiftDWord = 0;

    Prefix = Private->Prefix;
    for (i = 0; i <= LZ_MAX_CODE; i++) Prefix[i] = NO_SUCH_CODE;

    return GIF_OK;
}

/******************************************************************************
*   The LZ decompression routine:					      *
*   This version decompress the given gif file into 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 DGifDecompressLine(GifFileType *GifFile, GifPixelType *Line,
								int LineLen)
{
    int i = 0, j, CrntCode, EOFCode, ClearCode, CrntPrefix, LastCode, StackPtr;
    GifByteType *Stack, *Suffix;