/*
* Reads the GIF screen and the global color table.
*/
void GIFReadScreen(struct GIFScreen *screen, FILE *stream)
{
unsigned char buffer[7];
GIF_TRACE(("Reading Header\n"));
GIF_FREAD(buffer, 6, stream);
if (memcmp(buffer, "GIF", 3) != 0)
GIFError("Not a GIF file");
if ((memcmp(buffer + 3, "87a", 3) != 0) &&
(memcmp(buffer + 3, "89a", 3) != 0))
GIFWarning("Invalid GIF version number, not \"87a\" or \"89a\"");
GIF_TRACE(("Reading Logical Screen Descriptor\n"));
GIF_FREAD(buffer, 7, stream);
screen->Width = GIF_GETW(buffer + 0);
screen->Height = GIF_GETW(buffer + 2);
screen->GlobalColorFlag = (buffer[4] & 0x80) ? 1 : 0;
screen->ColorResolution = ((buffer[4] & 0x70) >> 3) + 1;
screen->SortFlag = (buffer[4] & 0x08) ? 1 : 0;
screen->GlobalNumColors = 2 << (buffer[4] & 0x07);
screen->Background = buffer[5];
screen->PixelAspectRatio = buffer[6];
if (screen->GlobalColorFlag)
{
GIF_TRACE(("Reading Global Color Table\n"));
GIF_FREAD(screen->GlobalColorTable, 3 * screen->GlobalNumColors,
stream);
}
GIF_TRACE(("Validating Logical Screen Descriptor\n"));
if (screen->Width == 0 || screen->Height == 0)
GIFError("Invalid image dimensions");
if (screen->Background > 0)
{
if ((screen->GlobalColorFlag &&
(screen->Background >= screen->GlobalNumColors)) ||
!screen->GlobalColorFlag)
{
#if 0 /* too noisy */
GIFWarning("Invalid background color index");
#endif
screen->Background = 0;
}
}
}
static int GIFReadDataBlock(unsigned char *buffer, FILE *stream)
{
int count;
GIF_FGETC(count, stream);
DataBlockSize = count;
if (count > 0)
{
GIF_FREAD(buffer, (unsigned int)count, stream);
}
return count;
}
/*
* Reads the next GIF image and local color table.
*/
static void GIFReadNextImage(struct GIFImage *image, FILE *stream)
{
struct GIFScreen *screen;
unsigned char buffer[9];
GIF_TRACE(("Reading Local Image Descriptor\n"));
GIF_FREAD(buffer, 9, stream);
if (image == NULL)
{
GIFSkipDataBlocks(stream);
return;
}
image->LeftPos = GIF_GETW(buffer + 0);
image->TopPos = GIF_GETW(buffer + 2);
image->Width = GIF_GETW(buffer + 4);
image->Height = GIF_GETW(buffer + 6);
image->LocalColorFlag = (buffer[8] & 0x80) ? 1 : 0;
image->InterlaceFlag = (buffer[8] & 0x40) ? 1 : 0;
image->SortFlag = (buffer[8] & 0x20) ? 1 : 0;
image->LocalNumColors = image->LocalColorFlag ? (2 << (buffer[8] & 0x07)) : 0;
if (image->LocalColorFlag)
{
GIF_TRACE(("Reading Local Color Table\n"));
GIF_FREAD(image->LocalColorTable, 3 * image->LocalNumColors, stream);
}
GIF_TRACE(("Validating Logical Screen Descriptor\n"));
screen = image->Screen;
if (image->Width == 0 || image->Height == 0 ||
image->LeftPos + image->Width > screen->Width ||
image->TopPos + image->Height > screen->Height)
GIFError("Invalid image dimensions");
GIFReadImageData(image, stream);
}
//函数调用了一个定位文件和读文件的函数
//调用前将pgif->fp定位到lzw开始,初始化pgif的调色板等显示参数
void GIFShowImage(GIF *pgif)
{
LZW lzw; //保存lzw解压缩参数
u8 temp;
GIFImageDescriptor imagedes; //gif图像描述
GraphicControlExtension gce; //图像扩展
u8 blockflag;
GIF_FREAD((UINT8*)&imagedes, sizeof(GIFImageDescriptor), pgif->fp);//帧图像描述块
pgif->Interlace = imagedes.ColorFlag.InterlaceFlag;
pgif->width = imagedes.Width;
pgif->height = imagedes.Height;
pgif->curx = 0;
pgif->cury = 0;
//lzw解码
GIF_FREAD(&temp, sizeof(u8),pgif->fp); //lzw编码长度
LzwInit(LzwTable, temp, &lzw,pgif->fp); //初始化管理结构体
LzwStart(&lzw,pgif); //解码输出
GIF_FSEEK(pgif->fp, 1, FSEEK_CUR); //跳过块结束标记
}
static void GIFSkipDataBlocks(FILE *stream)
{
int count;
unsigned char buffer[GIF_UCHAR_MAX + 1];
for ( ; ; )
{
GIF_FGETC(count, stream)
if (count > 0)
{
GIF_FREAD(buffer, (unsigned int)count, stream);
}
else
return;
}
}
//打开一个gif图像,需用GIFShowImage输出
//成功返回0
u8 GIFOpen(GIF *pgif,struct FileInfo *fp)
{
GIFLSDescriptor ls; //gif逻辑屏幕描述
u8 blockflag; //块标记 数据块:; ......
GraphicControlExtension gce; //图形扩展
pgif->fp = fp;
GIF_FSEEK(pgif->fp, sizeof(GIFHeader), FSEEK_SET); //跳过文件头
GIF_FREAD((UINT8*)&ls, sizeof(GIFLSDescriptor), pgif->fp);//逻辑屏幕描述 40byte
if (ls.ColorFlag.GlobalColorTableFlag) //如果有全局调色板
{
// pgif->globleClrTable = new GIFRGBITEM[1 << (ls.ColorFlag.Pixel + 1)];
GIF_FREAD((UINT8*)(pgif->globleClrTable), sizeof(GIFRGBITEM)*(1 << (ls.ColorFlag.Pixel + 1)), pgif->fp);
}
else
pgif->globleClrTable = NULL;
pgif->scWidth = ls.Width;
pgif->scHeight = ls.Height;
pgif->bkColorIndex = ls.BackColor;
pgif->DelayTime = 0; //初始化为静态图
pgif->TransparentColorFlag = 0; //默认无透明色
pgif->skimage = pgif->fp->File_CurOffset;
//读取各种控制块
while (1)
{
GIF_FREAD(&blockflag, 1, pgif->fp);
if (blockflag == ',') //帧图像数据(2C)
{
//保存该位置指针
return 0;
}
else if (blockflag == 0x21) //扩展块
{
GIF_FREAD(&blockflag, 1, pgif->fp);
if (blockflag == 0xF9) //图形控制扩展块
{
GIF_FREAD((UINT8*)&gce, sizeof(GraphicControlExtension), pgif->fp);
pgif->DelayTime = gce.DelayTime; //本帧图像延时
pgif->TransparentColorFlag = gce.Flag.TransparentColorFlag;//透明标志
pgif->DisposalMethod = gce.Flag.DisposalMethod; //处理方法
pgif->TransparentColorIndex = gce.TransparentColorIndex; //透明色引索
GIF_FSEEK(pgif->fp, 1, FSEEK_CUR); //块结束标记
}
else if (blockflag == 0xFF)//应用程序扩展
{
GIF_FSEEK(pgif->fp, sizeof(ApplicationExtension), FSEEK_CUR);
//跳过应用数据
while (1)
{
GIF_FREAD(&blockflag, 1, pgif->fp); //应用程序数据大小
if (blockflag == 0)break;
else
GIF_FSEEK(pgif->fp, blockflag, FSEEK_CUR);
}
}
else if (blockflag == 0xFE) //跳过注释扩展块
{
while (1)
{
GIF_FREAD(&blockflag, 1, pgif->fp);
if (blockflag == 0)break;
else
GIF_FSEEK(pgif->fp, blockflag, FSEEK_CUR);
}
}
else if (blockflag == 0x01) //跳过图形文本扩展
{
GIF_FSEEK(pgif->fp, sizeof(PlainTextExtension), FSEEK_CUR);
while (1)
{
GIF_FREAD(&blockflag, 1, pgif->fp);
if (blockflag == 0)break;
else
GIF_FSEEK(pgif->fp, blockflag, FSEEK_CUR);
}
}
else
{
return 2;
}
}
else if (blockflag == ';') //文件结束
{
return 3; //文件结束
}
else
{
return 1;
}
}
}
