Added bounds checking for triangles.

src/geom.c

@@ -0,0 +1,26 @@
+#include "include/geom.h"
+
+Tri* alltris[512];
+size_t allsize = 0;
+
+Tri* tri_init(Pt a, Pt b, Pt c) {
+    Tri* tri = malloc(sizeof(Tri));
+    *(alltris + allsize) = tri;
+    allsize++;
+    *tri = (Tri){a, b, c};
+    return tri;
+}
+
+bool tri_within(Pt pt, Tri* tri) {
+    double denom =
+        ((tri->b.y - tri->c.y) * (tri->a.x - tri->c.x) +
+         (tri->c.x - tri->b.x) * (tri->a.y - tri->c.y));
+    double a = ((tri->b.y - tri->c.y) * (pt.x - tri->c.x) +
+                (tri->c.x - tri->b.x) * (pt.y - tri->c.y)) /
+               denom;
+    double b = ((tri->c.y - tri->a.y) * (pt.x - tri->c.x) +
+                (tri->a.x - tri->c.x) * (pt.y - tri->c.y)) /
+               denom;
+    double c = 1 - a - b;
+    return 0 <= a && a <= 1 && 0 <= b && b <= 1 && 0 <= c && c <= 1;
+}