tharrison.c - plan9port - [fork] Plan 9 from user space
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       ---
       tharrison.c (708B)
       ---
            1 #include <u.h>
            2 #include <libc.h>
            3 #include "map.h"
            4 
            5 static double v3,u2,u3,a,b; /*v=view,p=obj,u=unit.y*/
            6 
            7 static int
            8 Xharrison(struct place *place, double *x, double *y)
            9 {
           10         double p1 = -place->nlat.c*place->wlon.s;
           11         double p2 = -place->nlat.c*place->wlon.c;
           12         double p3 = place->nlat.s;
           13         double d = b + u3*p2 - u2*p3;
           14         double t;
           15         if(d < .01)
           16                 return -1;
           17         t = a/d;
           18         if(v3*place->nlat.s < 1.)
           19                 return -1;
           20         *y = t*p2*u2 + (v3-t*(v3-p3))*u3;
           21         *x = t*p1;
           22         if(t < 0)
           23                 return 0;
           24         if(*x * *x + *y * *y > 16)
           25                 return -1;
           26         return 1;
           27 }
           28 
           29 proj
           30 harrison(double r, double alpha)
           31 {
           32         u2 = cos(alpha*RAD);
           33         u3 = sin(alpha*RAD);
           34         v3 = r;
           35         b = r*u2;
           36         a = 1 + b;
           37         if(r<1.001 || a<sqrt(r*r-1))
           38                 return 0;
           39         return Xharrison;
           40 }