ungif.c

这是一个开放源代码的与WINNT/WIN2K/WIN2003兼容的操作系统

          return GIF_ERROR;
    }

    return GIF_OK;
}

/******************************************************************************
 * This routine should be called before any attempt to read an image.
 * Note it is assumed the Image desc. header (',') has been read.
 *****************************************************************************/
static int
DGifGetImageDesc(GifFileType * GifFile) {

    int i, BitsPerPixel;
    GifByteType Buf[3];
    GifFilePrivateType *Private = (GifFilePrivateType *)GifFile->Private;
    SavedImage *sp;

    if (DGifGetWord(GifFile, &GifFile->Image.Left) == GIF_ERROR ||
        DGifGetWord(GifFile, &GifFile->Image.Top) == GIF_ERROR ||
        DGifGetWord(GifFile, &GifFile->Image.Width) == GIF_ERROR ||
        DGifGetWord(GifFile, &GifFile->Image.Height) == GIF_ERROR)
        return GIF_ERROR;
    if (READ(GifFile, Buf, 1) != 1) {
        return GIF_ERROR;
    }
    BitsPerPixel = (Buf[0] & 0x07) + 1;
    GifFile->Image.Interlace = (Buf[0] & 0x40);
    if (Buf[0] & 0x80) {    /* Does this image have local color map? */

        /*** FIXME: Why do we check both of these in order to do this?
         * Why do we have both Image and SavedImages? */
        if (GifFile->Image.ColorMap && GifFile->SavedImages == NULL)
            FreeMapObject(GifFile->Image.ColorMap);

        GifFile->Image.ColorMap = MakeMapObject(1 << BitsPerPixel, NULL);
        if (GifFile->Image.ColorMap == NULL) {
            return GIF_ERROR;
        }

        /* Get the image local color map: */
        for (i = 0; i < GifFile->Image.ColorMap->ColorCount; i++) {
            if (READ(GifFile, Buf, 3) != 3) {
                FreeMapObject(GifFile->Image.ColorMap);
                GifFile->Image.ColorMap = NULL;
                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];
        }
    } else if (GifFile->Image.ColorMap) {
        FreeMapObject(GifFile->Image.ColorMap);
        GifFile->Image.ColorMap = NULL;
    }

    if (GifFile->SavedImages) {
        if ((GifFile->SavedImages = realloc(GifFile->SavedImages,
                                      sizeof(SavedImage) *
                                      (GifFile->ImageCount + 1))) == NULL) {
            return GIF_ERROR;
        }
    } else {
        if ((GifFile->SavedImages = ungif_alloc(sizeof(SavedImage))) == NULL) {
            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);
        if (sp->ImageDesc.ColorMap == NULL) {
            return GIF_ERROR;
        }
    }
    sp->RasterBits = (unsigned 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.
 *****************************************************************************/
static int
DGifGetLine(GifFileType * GifFile,
            GifPixelType * Line,
            int LineLen) {

    GifByteType *Dummy;
    GifFilePrivateType *Private = (GifFilePrivateType *) GifFile->Private;

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

    if ((Private->PixelCount -= LineLen) > 0xffff0000UL) {
        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;
}

/******************************************************************************
 * Get an extension block (see GIF manual) from gif file. This routine only
 * returns the first data block, and DGifGetExtensionNext should be 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.
 *****************************************************************************/
static int
DGifGetExtension(GifFileType * GifFile,
                 int *ExtCode,
                 GifByteType ** Extension) {

    GifByteType Buf;

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

    return DGifGetExtensionNext(GifFile, Extension);
}

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

    GifByteType Buf;
    GifFilePrivateType *Private = (GifFilePrivateType *)GifFile->Private;

    if (READ(GifFile, &Buf, 1) != 1) {
        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) {
            return GIF_ERROR;
        }
    } else
        *Extension = NULL;

    return GIF_OK;
}

/******************************************************************************
 * Get 2 bytes (word) from the given file:
 *****************************************************************************/
static int
DGifGetWord(GifFileType * GifFile,
            GifWord *Word) {

    unsigned char c[2];

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

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

/******************************************************************************
 * 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).
 *****************************************************************************/
static int
DGifGetCodeNext(GifFileType * GifFile,
                GifByteType ** CodeBlock) {

    GifByteType Buf;
    GifFilePrivateType *Private = (GifFilePrivateType *)GifFile->Private;

    if (READ(GifFile, &Buf, 1) != 1) {
        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) {
            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;
    GifPrefixType *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;
    int j, CrntCode, EOFCode, ClearCode, CrntPrefix, LastCode, StackPtr;
    GifByteType *Stack, *Suffix;
    GifPrefixType *Prefix;
    GifFilePrivateType *Private = (GifFilePrivateType *) GifFile->Private;

    StackPtr = Private->StackPtr;
    Prefix = Private->Prefix;
    Suffix = Private->Suffix;
    Stack = Private->Stack;
    EOFCode = Private->EOFCode;
    ClearCode = Private->ClearCode;
    LastCode = Private->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 (DGifDecompressInput(GifFile, &CrntCode) == GIF_ERROR)
            return GIF_ERROR;

        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 || Private->PixelCount != 0) {
                return GIF_ERROR;
            }
            i++;
        } else if (CrntCode == ClearCode) {
            /* We need to start over again: */
            for (j = 0; j <= LZ_MAX_CODE; j++)
                Prefix[j] = NO_SUCH_CODE;
            Private->RunningCode = Private->EOFCode + 1;
            Private->RunningBits = Private->BitsPerPixel + 1;
            Private->MaxCode1 = 1 << Private->RunningBits;
            LastCode = Private->LastCode = 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++] = 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] == 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 == Private->RunningCode - 2) {
                        CrntPrefix = LastCode;
                        Suffix[Private->RunningCode - 2] =
                           Stack[StackPtr++] = DGifGetPrefixChar(Prefix,
                                                                 LastCode,
                                                                 ClearCode);
                    } else {
                        return GIF_ERROR;
                    }