map.c

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

		for(lon=lolon;lon<hilon;lon+=10.) {
			if(!seeable(lat,lon))
				continue;
			i = pnorm(lat);
			j = pnorm(lon);
			if((b=patch[i+9][j+18])&1)
				continue;
			fseek(ifile,b,0);
			while((ip=getc(ifile))>=0&&(jp=getc(ifile))>=0){
				if(ip!=(i&0377)||jp!=(j&0377))
					break;
				n = getshort(ifile);
				conn = 0;
				if(n > 0) {	/* absolute coordinates */
					kx = ky = 0;	/* set */
					for(k=0;k<n;k++){
						kx = SCALERATIO*getshort(ifile);
						ky = SCALERATIO*getshort(ifile);
						if (((k%delta) != 0) && (k != (n-1)))
							continue;
						conv(kx,&g.nlat);
						conv(ky,&g.wlon);
						conn = plotpt(&g,conn);
					}
				} else {	/* differential, scaled by SCALERATI0 */
					n = -n;
					kx = SCALERATIO*getshort(ifile);
					ky = SCALERATIO*getshort(ifile);
					for(k=0; k<n; k++) {
						c = getc(ifile);
						if(c&0200) c|= ~0177;
						kx += c;
						c = getc(ifile);
						if(c&0200) c|= ~0177;
						ky += c;
						if(k%delta!=0&&k!=n-1)
							continue;
						conv(kx,&g.nlat);
						conv(ky,&g.wlon);
						conn = plotpt(&g,conn);
					}
				}
				if(k==1) {
					conv(kx,&g.nlat);
					conv(ky,&g.wlon);
					plotpt(&g,conn);
				}
			}
		}
	fclose(ifile);
}

int
seeable(double lat0, double lon0)
{
	double x, y;
	double lat, lon;
	for(lat=lat0;lat<=lat0+10;lat+=2*grid[2])
		for(lon=lon0;lon<=lon0+10;lon+=2*grid[2])
			if(normproj(lat,lon,&x,&y)*vflag>0)
				return(1);
	return(0);
}

void
satellite(struct file *t)
{
	char sym[50];
	char lbl[50];
	double scale;
	register conn;
	double lat,lon;
	struct place place;
	static FILE *ifile = stdin;
	if(t->name[0]!='-'||t->name[1]!=0) {
		fclose(ifile);
		if((ifile=fopen(t->name,"r"))==NULL)
			filerror("can't find track", t->name);
	}
	comment("track",t->name);
	colorx(t->color);
	pen(t->style);
	for(;;) {
		conn = 0;
		while(!feof(ifile) && fscanf(ifile,"%lf%lf",&lat,&lon)==2){
			latlon(lat,lon,&place);
			if(fscanf(ifile,"%1s",lbl) == 1) {
				if(strchr("+-.0123456789",*lbl)==0)
					break;
				ungetc(*lbl,ifile);
			}
			conn = plotpt(&place,conn);
		}
		if(feof(ifile))
			return;
		fscanf(ifile,"%[^\n]",lbl+1);
		switch(*lbl) {
		case '"':
			if(plotpt(&place,conn))
				text(lbl+1);
			break;
		case ':':
		case '!':
			if(sscanf(lbl+1,"%s %lf",sym,&scale) <= 1)
				scale = 1;
			if(plotpt(&place,conn?conn:-1)) {
				int r = *lbl=='!'?0:rflag?-1:1;
				pen(SOLID);
				if(putsym(&place,sym,scale,r) == 0)
					text(lbl);
				pen(t->style);
			}
			break;
		default:
			if(plotpt(&place,conn))
				text(lbl);
			break;
		}
	}
}

int
pnorm(double x)
{
	int i;
	i = x/10.;
	i %= 36;
	if(i>=18) return(i-36);
	if(i<-18) return(i+36);
	return(i);
}

void
error(char *s)
{
	fprintf(stderr,"map: \r\n%s\n",s);
	exits("error");
}

void
filerror(char *s, char *f)
{
	fprintf(stderr,"\r\n%s %s\n",s,f);
	exits("error");
}

char *
mapindex(char *s)
{
	char *t = malloc(strlen(s)+3);
	strcpy(t,s);
	strcat(t,".x");
	return t;
}

#define NOPT 32767
static ox = NOPT, oy = NOPT;

int
cpoint(int xi, int yi, int conn)
{
	int dx = abs(ox-xi);
	int dy = abs(oy-yi);
	if(!xflag && (xi<left||xi>=right || yi<bottom||yi>=top)) {
		ox = oy = NOPT;
		return 0;
	}
	if(conn == -1)		/* isolated plotting symbol */
		{}
	else if(!conn)
		point(xi,yi);
	else {
		if(dx+dy>longlines) {
			ox = oy = NOPT;	/* don't leap across cuts */
			return 0;
		}
		if(dx || dy)
			vec(xi,yi);
	}
	ox = xi, oy = yi;
	return dx+dy<=2? 2: 1;	/* 2=very near; see dogrid */
}


struct place oldg;

int
plotpt(struct place *g, int conn)
{
	int kx,ky;
	int ret;
	double cutlon;
	if(!inlimits(g)) {
		return(0);
}
	normalize(g);
	if(!inwindow(g)) {
		return(0);
}
	switch((*cut)(g,&oldg,&cutlon)) {
	case 2:
		if(conn) {
			ret = duple(g,cutlon)|duple(g,cutlon);
			oldg = *g;
			return(ret);
		}
	case 0:
		conn = 0;
	default:	/* prevent diags about bad return value */
	case 1:
		oldg = *g;
		ret = doproj(g,&kx,&ky);
		if(ret==0 || !onlimb && ret*vflag<=0)
			return(0);
		ret = cpoint(kx,ky,conn);
		return ret;
	}
}

int
doproj(struct place *g, int *kx, int *ky)
{
	int i;
	double x,y,x1,y1;
/*fprintf(stderr,"dopr1 %f %f \n",g->nlat.l,g->wlon.l);*/
	i = fixproj(g,&x,&y);
	if(i == 0)
		return(0);
	if(rflag)
		x = -x;
/*fprintf(stderr,"dopr2 %f %f\n",x,y);*/
	if(!inpoly(x,y)) {
		return 0;
}
	x1 = x - xcent;
	y1 = y - ycent;
	x = (x1*crot.c - y1*crot.s + xoff)*scaling;
	y = (x1*crot.s + y1*crot.c + yoff)*scaling;
	*kx = x + (x>0?.5:-.5);
	*ky = y + (y>0?.5:-.5);
	return(i);
}

int
duple(struct place *g, double cutlon)
{
	int kx,ky;
	int okx,oky;
	struct place ig;
	revlon(g,cutlon);
	revlon(&oldg,cutlon);
	ig = *g;
	invert(&ig);
	if(!inlimits(&ig))
		return(0);
	if(doproj(g,&kx,&ky)*vflag<=0 ||
	   doproj(&oldg,&okx,&oky)*vflag<=0)
		return(0);
	cpoint(okx,oky,0);
	cpoint(kx,ky,1);
	return(1);
}

void
revlon(struct place *g, double cutlon)
{
	g->wlon.l = reduce(cutlon-reduce(g->wlon.l-cutlon));
	sincos(&g->wlon);
}


/*	recognize problems of cuts
 *	move a point across cut to side of its predecessor
 *	if its very close to the cut
 *	return(0) if cut interrupts the line
 *	return(1) if line is to be drawn normally
 *	return(2) if line is so close to cut as to
 *	be properly drawn on both sheets
*/

int
picut(struct place *g, struct place *og, double *cutlon)
{
	*cutlon = PI;
	return(ckcut(g,og,PI));
}

int
nocut(struct place *g, struct place *og, double *cutlon)
{
	USED(g, og, cutlon);
/*
#pragma	ref g
#pragma	ref og
#pragma	ref cutlon
*/
	return(1);
}

int
ckcut(struct place *g1, struct place *g2, double lon)
{
	double d1, d2;
	double f1, f2;
	int kx,ky;
	d1 = reduce(g1->wlon.l -lon);
	d2 = reduce(g2->wlon.l -lon);
	if((f1=fabs(d1))<FUZZ)
		d1 = diddle(g1,lon,d2);
	if((f2=fabs(d2))<FUZZ) {
		d2 = diddle(g2,lon,d1);
		if(doproj(g2,&kx,&ky)*vflag>0)
			cpoint(kx,ky,0);
	}
	if(f1<FUZZ&&f2<FUZZ)
		return(2);
	if(f1>PI*TWO_THRD||f2>PI*TWO_THRD)
		return(1);
	return(d1*d2>=0);
}

double
diddle(struct place *g, double lon, double d)
{
	double d1;
	d1 = FUZZ/2;
	if(d<0)
		d1 = -d1;
	g->wlon.l = reduce(lon+d1);
	sincos(&g->wlon);
	return(d1);
}

double
reduce(double lon)
{
	if(lon>PI)
		lon -= 2*PI;
	else if(lon<-PI)
		lon += 2*PI;
	return(lon);
}


double tetrapt = 35.26438968;	/* atan(1/sqrt(2)) */

void
dogrid(double lat0, double lat1, double lon0, double lon1)
{
	double slat,slon,tlat,tlon;
	register int conn, oconn;
	slat = tlat = slon = tlon = 0;
	if(lat1>lat0)
		slat = tlat = fmin(grid[2],dlat);
	else
		slon = tlon = fmin(grid[2],dlon);;
	conn = oconn = 0;
	while(lat0<=lat1&&lon0<=lon1) {
		conn = gridpt(lat0,lon0,conn);
		if(projection==Xguyou&&slat>0) {
			if(lat0<-45&&lat0+slat>-45)
				conn = gridpt(-45.,lon0,conn);
			else if(lat0<45&&lat0+slat>45)
				conn = gridpt(45.,lon0,conn);
		} else if(projection==Xtetra&&slat>0) {
			if(lat0<-tetrapt&&lat0+slat>-tetrapt) {
				gridpt(-tetrapt-.001,lon0,conn);
				conn = gridpt(-tetrapt+.001,lon0,0);
			}
			else if(lat0<tetrapt&&lat0+slat>tetrapt) {
				gridpt(tetrapt-.001,lon0,conn);
				conn = gridpt(tetrapt+.001,lon0,0);
			}
		}
		if(conn==0 && oconn!=0) {
			if(slat+slon>.05) {
				lat0 -= slat;	/* steps too big */
				lon0 -= slon;	/* or near bdry */
				slat /= 2;
				slon /= 2;
				conn = oconn = gridpt(lat0,lon0,conn);
			} else
				oconn = 0;
		} else {
			if(conn==2) {
				slat = tlat;
				slon = tlon;
				conn = 1;
			}
			oconn = conn;
	 	}
		lat0 += slat;
		lon0 += slon;
	}
	gridpt(lat1,lon1,conn);
}

static gridinv;		/* nonzero when doing window bounds */

int
gridpt(double lat, double lon, int conn)
{
	struct place g;
/*fprintf(stderr,"%f %f\n",lat,lon);*/
	latlon(lat,lon,&g);
	if(gridinv)
		invert(&g);
	return(plotpt(&g,conn));
}

/* win=0 ordinary grid lines, win=1 window lines */

void
dobounds(double lolat, double hilat, double lolon, double hilon, int win)
{
	gridinv = win;
	if(lolat>-90 || win && (poles&1)!=0)
		dogrid(lolat+FUZZ,lolat+FUZZ,lolon,hilon);
	if(hilat<90 || win && (poles&2)!=0)
		dogrid(hilat-FUZZ,hilat-FUZZ,lolon,hilon);
	if(hilon-lolon<360 || win && cut==picut) {
		dogrid(lolat,hilat,lolon+FUZZ,lolon+FUZZ);
		dogrid(lolat,hilat,hilon-FUZZ,hilon-FUZZ);
	}
	gridinv = 0;
}

static void
dolimb(void)
{
	double lat, lon;
	double res = fmin(dlat, dlon)/4;
	int conn = 0;
	int newconn;
	if(limb == 0)
		return;
	onlimb = gridinv = 1;
	for(;;) {
		newconn = (*limb)(&lat, &lon, res);
		if(newconn == -1)
			break;
		conn = gridpt(lat, lon, conn*newconn);
	}
	onlimb = gridinv = 0;
}


void
radbds(double *w, double *rw)
{
	int i;
	for(i=0;i<4;i++)
		rw[i] = w[i]*RAD;
	rw[0] -= FUZZ;
	rw[1] += FUZZ;
	rw[2] -= FUZZ;
	rw[3] += FUZZ;
}

void
windlim(void)
{
	double center = orientation[0];
	double colat;
	if(center>90)
		center = 180 - center;
	if(center<-90)
		center = -180 - center;
	if(fabs(center)>90)
		error("unreasonable orientation");
	colat = 90 - window[0];
	if(center-colat>limits[0])
		limits[0] = center - colat;
	if(center+colat<limits[1])
		limits[1] = center + colat;
}


short
getshort(FILE *f)
{
	int c, r;
	c = getc(f);
	r = (c | getc(f)<<8);
	if (r&0x8000)
		r |= ~0xFFFF;	/* in case short > 16 bits */
	return r;
}

double
fmin(double x, double y)
{
	return(x<y?x:y);
}

double
fmax(double x, double y)
{
	return(x>y?x:y);
}

void
clamp(double *px, double v)
{
	*px = (v<0?fmax:fmin)(*px,v);
}

void
pathnames(void)
{
	int i;
	char *t, *indexfile, *name;
	FILE *f, *fx;
	for(i=0; i<nfile; i++) {
		name = file[i].name;
		if(*name=='/')
			continue;
		indexfile = mapindex(name);
			/* ansi equiv of unix access() call */
		f = fopen(name, "r");
		fx = fopen(indexfile, "r");
		if(f) fclose(f);
		if(fx) fclose(fx);
		free(indexfile);
		if(f && fx)
			continue;
		t = malloc(strlen(name)+strlen(mapdir)+2);
		strcpy(t,mapdir);
		strcat(t,"/");
		strcat(t,name);
		file[i].name = t;
	}
}

void
clipinit(void)
{
	register i;
	double s,t;
	if(nvert<=0)
		return;
	for(i=0; i<nvert; i++) {	/*convert latlon to xy*/
		if(normproj(v[i].x,v[i].y,&v[i].x,&v[i].y)==0)
			error("invisible clipping vertex");
	}
	if(nvert==2) {			/*rectangle with diag specified*/
		nvert = 4;
		v[2] = v[1];
		v[1].x=v[0].x, v[1].y=v[2].y, v[3].x=v[2].x, v[3].y=v[0].y;
	}	
	v[nvert] = v[0];
	v[nvert+1] = v[1];
	s = 0;
	for(i=1; i<=nvert; i++) {	/*test for convexity*/
		t = (v[i-1].x-v[i].x)*(v[i+1].y-v[i].y) -
		    (v[i-1].y-v[i].y)*(v[i+1].x-v[i].x);
		if(t<-FUZZ && s>=0) s = 1;
		if(t>FUZZ && s<=0) s = -1;
		if(-FUZZ<=t&&t<=FUZZ || t*s>0) {
			s = 0;
			break;
		}
	}
	if(s==0)
		error("improper clipping polygon");
	for(i=0; i<nvert; i++) {	/*edge equation ax+by=c*/
		e[i].a = s*(v[i+1].y - v[i].y);
		e[i].b = s*(v[i].x - v[i+1].x);
		e[i].c = s*(v[i].x*v[i+1].y - v[i].y*v[i+1].x);
	}
}

int
inpoly(double x, double y)
{
	register i;
	for(i=0; i<nvert; i++) {
		register struct edge *ei = &e[i];
		double val = x*ei->a + y*ei->b - ei->c;
		if(val>10*FUZZ)
			return(0);
	}
	return 1;
}

void
realcut()
{
	struct place g;
	double lat;
	
	if(cut != picut)	/* punt on unusual cuts */
		return;
	for(lat=window[0]; lat<=window[1]; lat+=grid[2]) {
		g.wlon.l = PI;
		sincos(&g.wlon);
		g.nlat.l = lat*RAD;
		sincos(&g.nlat);
		if(!inwindow(&g)) {
			break;
}
		invert(&g);
		if(inlimits(&g)) {
			return;
}
	}
	longlines = shortlines = LONGLINES;
	cut = nocut;		/* not necessary; small eff. gain */
}