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#include <u.h>
#include <libc.h>
#include <geometry.h>
int
lineXline(Point2 *r, Point2 p0, Point2 p1, Point2 p2, Point2 p3)
{
Point2 dp[2], xp;
double m[2], c[2];
dp[0] = subpt2(p1, p0); m[0] = dp[0].y/dp[0].x; c[0] = p0.y - m[0]*p0.x;
fprint(2, "#1 := %gx + %g\n", m[0], c[0]);
dp[1] = subpt2(p3, p2); m[1] = dp[1].y/dp[1].x; c[1] = p2.y - m[1]*p2.x;
fprint(2, "#2 := %gx + %g\n", m[1], c[1]);
if(m[0] == m[1]){
if(c[0] == c[1]){ /* coincident */
r[0] = p0;
r[1] = p1;
return 2;
}
/* parallel */
return 0;
}
/* intersecting */
xp.x = (c[1]-c[0])/(m[0]-m[1]);
xp.y = m[0]*xp.x + c[0];
xp.w = 1;
r[0] = xp;
return 1;
}
void
usage(void)
{
fprint(2, "usage: %s x0 y0 x1 y1 x2 y2 x3 y3\n", argv0);
exits("usage");
}
void
main(int argc, char *argv[])
{
Point2 p0, p1, p2, p3, r[2];
int n;
GEOMfmtinstall();
ARGBEGIN{
default: usage();
}ARGEND
if(argc != 8)
usage();
p0.x = strtod(argv[0], nil); p0.y = strtod(argv[1], nil);
p1.x = strtod(argv[2], nil); p1.y = strtod(argv[3], nil);
p2.x = strtod(argv[4], nil); p2.y = strtod(argv[5], nil);
p3.x = strtod(argv[6], nil); p3.y = strtod(argv[7], nil);
n = lineXline(r, p0, p1, p2, p3);
while(n--)
print("p%d: %v\n", n, r[n]);
exits(nil);
}
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