gif.c

一个简单的C语言写的GIF算法

我也很想帮你，但是我这里只有一个写入GIF的，可以运行的，你看看它的代码  
  读取是写的逆操作，应该对你有帮助  
   
  /*--GIF动画生成.  
    程序中type的值为2则按16色的格式生成动画;type的值为3则按256色  
    mode的值为0按顺序方式压缩数据,mode的值为1则按交叉方式压缩  
    数据,生其的动画文件可直接在浏览器中播放.  
  TC20   small模式下编译通过--*/  
  #include<stdio.h>  
  #include<graphics.h>  
   
  #define   MAXCODES   4096  
  #define   TABLESIZES   4999  
   
  int   left,top,width,right,bottom,type,mode;  
  unsigned   char   blockbuf[256],colorbits;  
  int   clearcode,eofcode,encode;  
  int   encodetable[TABLESIZES];  
  int   initbits,runbits,shiftbits;  
  int   maxcodesize,bytecount;  
  unsigned   long   tempcodes;  
  int   linestart[]={0,4,2,1};  
  int   rowcount[]={8,8,4,2};  
   
  void   getcolortable(int   colortable[16][3])/*   设置16色颜色表   */  
  {int   i,j;  
    int   color[16]={0,1,2,3,4,5,22,7,56,57,58,59,60,61,62,63};  
    for(i=0;i<16;i++)  
    {j=color[i];  
      if(i==6)j=20;  
      outportb(0x3c7,((unsigned   char)j));  
      colortable[i][0]=inportb(0x3c9);  
      colortable[i][1]=inportb(0x3c9);  
      colortable[i][2]=inportb(0x3c9);  
    }  
  }  
   
  void   globalheader(FILE   *   fp)  
  {int   i,colornum,colortable[16][3];  
    unsigned   char   pal[768];  
    struct   globalhead{  
              unsigned   char   signature[6];  
              unsigned   int   width;  
              unsigned   int   height;  
              unsigned   char   flag;  
              unsigned   char   color;  
              unsigned   char   ratio;  
    }gif;  
    memcpy(gif.signature,"GIF89a",6);/*   Gif   数字签名   GIF89a   */  
    gif.width=right-left;  
    gif.height=bottom-top;  
   
    if(type==2)  
      colorbits=4;  
    else   colorbits=8;/*   色深   */  
    gif.flag=(colorbits-1<<4)|(colorbits-1);  
    if(type!=1)gif.flag|=0x80;  
   
    gif.color=0;gif.ratio=0;  
    fwrite(&gif,1,13,fp);/*   GIF   文件头：13BYTE   */  
   
    if(gif.flag&0x80){  
        for(i=0;i<768;i++)pal[i]=0;  
        getcolortable(colortable);  
        for(i=0;i<16;i++)  
            {pal[3*i]=colortable[i][0]<<2;  
              pal[3*i+1]=colortable[i][1]<<2;  
              pal[3*i+2]=colortable[i][2]<<2;  
            }  
        colornum=3*(1<<colorbits);  
        fwrite(&pal,1,colornum,fp);  
    }  
  }  
   
  void   localheader(FILE   *   fp)  
  {struct   localhead{  
        unsigned   char   label;  
        unsigned   int   left;  
        unsigned   int   top;  
        unsigned   int   width;  
        unsigned   int   height;  
        unsigned   char   flag;  
      }image;  
    image.label=0x2c;image.left=0;image.top=0;  
    image.width=right-left;image.height=bottom-top;  
    image.flag=colorbits-1;  
    if(mode)image.flag|=0x40;  
    fwrite(&image,1,10,fp);  
  }  
   
  void   cleartable()  
  {int   count;  
    encode=eofcode+1;runbits=initbits+1;maxcodesize=1<<runbits;  
    for(count=0;count<TABLESIZES;count++)encodetable[count]=0;  
  }  
   
  void   savecode(FILE   *   fp)  
  {blockbuf[0]=bytecount;bytecount++;  
    fwrite(blockbuf,1,bytecount,fp);  
    bytecount=0;  
  }  
   
  void   fillblockbuf(FILE   *   fp,int   code)  
  {tempcodes|=(unsigned   long)code<<shiftbits;shiftbits+=runbits;  
    while(shiftbits>=8)  
    {blockbuf[++bytecount]=tempcodes&0x00ff;  
      if(bytecount==255)savecode(fp);tempcodes>>=8;shiftbits-=8;  
    }  
  }  
   
  void   LZWimage(FILE   *   fp)   /*   写入LZW数据   */  
  {unsigned   char   suffixtable[TABLESIZES],bytebuf[640],now;  
    int   i,prefixtable[TABLESIZES],prefixcode,suffixcode,index,off;  
    unsigned   int   width,height,row,dot,online;  
    width=right-left;height=bottom-top;initbits=colorbits;  
   
    if(initbits>8)exit(1);/*   不支持高于256色   */  
   
    fputc(initbits,fp);  
    clearcode=1<<initbits;  
    eofcode=clearcode+1;  
    bytecount=shiftbits=0;  
    tempcodes=0;  
    cleartable();/*   清空索引表   */  
   
    fillblockbuf(fp,clearcode);  
    for(row=0,online=0,now=0;row<height;row++)/*   处理所有行   */  
    {  
      for(i=0;i<width;i++)  
        bytebuf[i]=getpixel(left+i,top+online);  
        if(mode){online+=rowcount[now];  
          if(online>=height){now++;online=linestart[now];}  
          }  
        else   online++;  
        if(row==0){prefixcode=bytebuf[0];dot=1;}  
        else   dot=0;  
   
        while(dot<width)/*   压缩一行信息   */  
        {suffixcode=bytebuf[dot++];  
          index=prefixcode^(suffixcode<<4);  
          if(index==0)off=1;else   off=TABLESIZES-index;  
          while(1)  
          {if(encodetable[index]==0)  
            {fillblockbuf(fp,prefixcode);  
              if(encode==MAXCODES)  
              {fillblockbuf(fp,clearcode);cleartable();}  
              else  
              {if(encode==maxcodesize)  
                {maxcodesize<<=1;runbits++;  
              }  
              prefixtable[index]=prefixcode;  
              suffixtable[index]=suffixcode;encodetable[index]=encode++;  
            }  
            prefixcode=suffixcode;break;  
          }  
          if(prefixtable[index]==prefixcode&&suffixtable[index]==suffixcode)  
          {prefixcode=encodetable[index];break;}  
          else  
          {index-=off;if(index<0)index+=TABLESIZES;}  
        }  
      }  
    }  
    fillblockbuf(fp,prefixcode);fillblockbuf(fp,eofcode);  
    if(shiftbits>0||bytecount>0)  
    {blockbuf[++bytecount]=tempcodes&0x00ff;savecode(fp);}  
    fputc(0,fp);  
  }  
   
  void   applyblock(FILE   *   fp)  
  {  
    struct  
    {unsigned   char   extension;  
      unsigned   char   label;  
      unsigned   char   size;  
      char   identifier[8];  
      char   code[3];  
      char   data[4];  
      unsigned   char   teminator;  
    }application;  
   
    application.extension=0x21;  
    application.label=0xff;application.size=11;  
    memcpy(application.identifier,"NETSCAPE",8);  
    memcpy(application.code,"2.0",3);application.data[0]=3;  
    application.data[1]=1;application.data[2]=0xe8;application.data[3]=3;  
    application.teminator=0;  
    fwrite(&application,1,19,fp);  
  }  
   
  void   controlblock(FILE   *   fp,int   delaytime)  
  {struct{unsigned   char   extension;  
  unsigned   char   label;  
  unsigned   char   size;  
  unsigned   char   field;  
  unsigned   int   delaytime;  
  unsigned   char   colorindex;  
  unsigned   char   terminator;  
                }control;  
    control.extension=0x21;control.label=0xf9;  
    control.size=4;control.field=0;  
    control.delaytime=delaytime;control.colorindex=0;  
    control.terminator=0;fwrite(&control,1,8,fp);  
  }  
   
   
  void   formgif()/*   使用GIF函数，输出GIF图象   */  
  {int   i,charsize=4;  
    char   *   text="GIF   Animator!";  
    FILE   *   fp;  
    settextstyle(TRIPLEX_FONT,HORIZ_DIR,charsize);  
    left=220;top=200;right=420;bottom=280;type=3;mode=0;  
    if((fp=fopen("animator.gif","wb"))==NULL)  
          {printf("Can   not   create   Gif   file!\n");exit(1);}  
   
    globalheader(fp);   /*   写入全局头   */  
    applyblock(fp);   /*   写入应用程序声明头   */  
   
    for(i=1;i<22;i++)  
      {setcolor(GREEN);outtextxy(right-20*i,top+20,text);  
   
        controlblock(fp,20);   /*   写入控制块   */  
        localheader(fp);   /*   写入局部头   */  
        LZWimage(fp);   /*   写入LZW数据   */  
   
        delay(200);setcolor(BLACK);outtextxy(right-20*i,top+20,text);  
      }  
    fputc(';',fp);fclose(fp);  
  }  
  main()  
  {int   gd,gm,gerror;  
    detectgraph(&gd,&gm);initgraph(&gd,&gm,"");  
    cleardevice();formgif();closegraph();  
  }