From 28994509cc11ac6a5443054dfae1fedfb69039bc Mon Sep 17 00:00:00 2001
From: rsc <devnull@localhost>
Date: Wed, 21 Apr 2004 22:19:33 +0000
Subject: Why not?

---
 src/cmd/map/libmap/hex.c | 122 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 122 insertions(+)
 create mode 100644 src/cmd/map/libmap/hex.c

(limited to 'src/cmd/map/libmap/hex.c')

diff --git a/src/cmd/map/libmap/hex.c b/src/cmd/map/libmap/hex.c
new file mode 100644
index 00000000..851f138f
--- /dev/null
+++ b/src/cmd/map/libmap/hex.c
@@ -0,0 +1,122 @@
+#include <u.h>
+#include <libc.h>
+#include "map.h"
+
+#define BIG 1.e15
+#define HFUZZ .0001
+
+static double hcut[3] ;
+static double kr[3] = { .5, -1., .5 };
+static double ki[3] = { -1., 0., 1. }; 	/*to multiply by sqrt(3)/2*/
+static double cr[3];
+static double ci[3];
+static struct place hem;
+static struct coord twist;
+static double  rootroot3, hkc;
+static double w2;
+static double rootk;
+
+static void
+reflect(int i, double wr, double wi, double *x, double *y)
+{
+	double pr,pi,l;
+	pr = cr[i]-wr;
+	pi = ci[i]-wi;
+	l = 2*(kr[i]*pr + ki[i]*pi);
+	*x = wr + l*kr[i];
+	*y = wi + l*ki[i];
+}
+
+static int
+Xhex(struct place *place, double *x, double *y)
+{
+	int ns;
+	int i;
+	double zr,zi;
+	double sr,si,tr,ti,ur,ui,vr,vi,yr,yi;
+	struct place p;
+	copyplace(place,&p);
+	ns = place->nlat.l >= 0;
+	if(!ns) {
+		p.nlat.l = -p.nlat.l;
+		p.nlat.s = -p.nlat.s;
+	}
+	if(p.nlat.l<HFUZZ) {
+		for(i=0;i<3;i++)
+			if(fabs(reduce(p.wlon.l-hcut[i]))<HFUZZ) {
+				if(i==2) {
+					*x = 2*cr[0] - cr[1];
+					*y = 0;
+				} else {
+					*x = cr[1];
+					*y = 2*ci[2*i];
+				}
+				return(1);
+			}
+		p.nlat.l = HFUZZ;
+		sincos(&p.nlat);
+	}
+	norm(&p,&hem,&twist);
+	Xstereographic(&p,&zr,&zi);
+	zr /= 2;
+	zi /= 2;
+	cdiv(1-zr,-zi,1+zr,zi,&sr,&si);
+	csq(sr,si,&tr,&ti);
+	ccubrt(1+3*tr,3*ti,&ur,&ui);
+	csqrt(ur-1,ui,&vr,&vi);
+	cdiv(rootroot3+vr,vi,rootroot3-vr,-vi,&yr,&yi);
+	yr /= rootk;
+	yi /= rootk;
+	elco2(fabs(yr),yi,hkc,1.,1.,x,y);
+	if(yr < 0)
+		*x = w2 - *x;
+	if(!ns) reflect(hcut[0]>place->wlon.l?0:
+			hcut[1]>=place->wlon.l?1:
+			2,*x,*y,x,y);
+	return(1);
+}
+
+proj
+hex(void)
+{
+	int i;
+	double t;
+	double root3;
+	double c,d;
+	struct place p;
+	hcut[2] = PI;
+	hcut[1] = hcut[2]/3;
+	hcut[0] = -hcut[1];
+	root3 = sqrt(3.);
+	rootroot3 = sqrt(root3);
+	t = 15 -8*root3;
+	hkc = t*(1-sqrt(1-1/(t*t)));
+	elco2(BIG,0.,hkc,1.,1.,&w2,&t);
+	w2 *= 2;
+	rootk = sqrt(hkc);
+	latlon(90.,90.,&hem);
+	latlon(90.,0.,&p);
+	Xhex(&p,&c,&t);
+	latlon(0.,0.,&p);
+	Xhex(&p,&d,&t);
+	for(i=0;i<3;i++) {
+		ki[i] *= root3/2;
+		cr[i] = c + (c-d)*kr[i];
+		ci[i] = (c-d)*ki[i];
+	}
+	deg2rad(0.,&twist);
+	return(Xhex);
+}
+
+int
+hexcut(struct place *g, struct place *og, double *cutlon)
+{
+	int t,i;
+	if(g->nlat.l>=-HFUZZ&&og->nlat.l>=-HFUZZ)
+		return(1);
+	for(i=0;i<3;i++) {
+		t = ckcut(g,og,*cutlon=hcut[i]);
+		if(t!=1) return(t);
+	}
+	return(1);
+}
-- 
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