c=c1;if (c==0)c=c2; if(c&1==1){y=y0+(y2-y0)*(x1-x0)/(x2-x0);x=x1;} else if(c&2==2){y=y0+(y2-y0)*(xr-x0)/(x2-x0); x=xr; else if(c&4==4){x=x0+(x2-x0)*(yb-y0)/y2-y0); y=yb; else if(c&8==8){x=x0+(x2-x0)*(yt-y0)/(y2-y0); y=yt; if (c==c1) {x0=x;y0=y;makecode(x,y,c1);} else {x2=x;y2=y;makecode(x,y,c2);} showline(x0,y0,x2,y2);∥显示可见线段c=c1; if (c==0) c=c2; if (c&1==1){y=y0+(y2-y0)*(x1-x0)/(x2-x0); x=x1;} else if (c&2==2){y=y0+(y2-y0)*(xr-x0)/(x2-x0); x=xr;} else if (c&4==4){x=x0+(x2-x0)*(yb-y0)/(y2-y0); y=yb;} else if (c&8==8){x=x0+(x2-x0)*(yt-y0)/(y2-y0); y=yt;} if (c==c1) {x0=x; y0=y; makecode(x, y, c1);} else {x2=x; y2=y; makecode(x, y, c2);} } showline(x0, y0, x2, y2); //显示可见线段}