ref: 76ada2d705f21dd5ed753fdafe00849afa7f6edd
parent: 9a7852993c538212d5e14aa34c49ba7d990aca76
author: rodri <rgl@antares-labs.eu>
date: Sat Jan 27 09:14:06 EST 2024
simple line-line intersection algorithm.
--- /dev/null
+++ b/lineXline.c
@@ -1,0 +1,64 @@
+#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);
+}