Data commit

Task/Determine-if-two-triangles-overlap/C/determine-if-two-triangles-overlap.c

@@ -0,0 +1,144 @@
+#include <errno.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+typedef struct {
+    double x, y;
+} Point;
+
+double det2D(const Point * const p1, const Point * const p2, const Point * const p3) {
+    return p1->x * (p2->y - p3->y)
+        + p2->x * (p3->y - p1->y)
+        + p3->x * (p1->y - p2->y);
+}
+
+void checkTriWinding(Point * p1, Point * p2, Point * p3, bool allowReversed) {
+    double detTri = det2D(p1, p2, p3);
+    if (detTri < 0.0) {
+        if (allowReversed) {
+            double t = p3->x;
+            p3->x = p2->x;
+            p2->x = t;
+
+            t = p3->y;
+            p3->y = p2->y;
+            p2->y = t;
+        } else {
+            errno = 1;
+        }
+    }
+}
+
+bool boundaryCollideChk(const Point *p1, const Point *p2, const Point *p3, double eps) {
+    return det2D(p1, p2, p3) < eps;
+}
+
+bool boundaryDoesntCollideChk(const Point *p1, const Point *p2, const Point *p3, double eps) {
+    return det2D(p1, p2, p3) <= eps;
+}
+
+bool triTri2D(Point t1[], Point t2[], double eps, bool allowReversed, bool onBoundary) {
+    bool(*chkEdge)(Point*, Point*, Point*, double);
+    int i;
+
+    // Triangles must be expressed anti-clockwise
+    checkTriWinding(&t1[0], &t1[1], &t1[2], allowReversed);
+    if (errno != 0) {
+        return false;
+    }
+    checkTriWinding(&t2[0], &t2[1], &t2[2], allowReversed);
+    if (errno != 0) {
+        return false;
+    }
+
+    if (onBoundary) {
+        // Points on the boundary are considered as colliding
+        chkEdge = boundaryCollideChk;
+    } else {
+        // Points on the boundary are not considered as colliding
+        chkEdge = boundaryDoesntCollideChk;
+    }
+
+    //For edge E of trangle 1,
+    for (i = 0; i < 3; ++i) {
+        int j = (i + 1) % 3;
+
+        //Check all points of trangle 2 lay on the external side of the edge E. If
+        //they do, the triangles do not collide.
+        if (chkEdge(&t1[i], &t1[j], &t2[0], eps) &&
+            chkEdge(&t1[i], &t1[j], &t2[1], eps) &&
+            chkEdge(&t1[i], &t1[j], &t2[2], eps)) {
+            return false;
+        }
+    }
+
+    //For edge E of trangle 2,
+    for (i = 0; i < 3; i++) {
+        int j = (i + 1) % 3;
+
+        //Check all points of trangle 1 lay on the external side of the edge E. If
+        //they do, the triangles do not collide.
+        if (chkEdge(&t2[i], &t2[j], &t1[0], eps) &&
+            chkEdge(&t2[i], &t2[j], &t1[1], eps) &&
+            chkEdge(&t2[i], &t2[j], &t1[2], eps))
+            return false;
+    }
+
+    //The triangles collide
+    return true;
+}
+
+int main() {
+    {
+        Point t1[] = { {0, 0}, {5, 0}, {0, 5} };
+        Point t2[] = { {0, 0}, {5, 0}, {0, 6} };
+        printf("%d,true\n", triTri2D(t1, t2, 0.0, false, true));
+    }
+
+    {
+        Point t1[] = { {0, 0}, {0, 5}, {5, 0} };
+        Point t2[] = { {0, 0}, {0, 5}, {5, 0} };
+        printf("%d,true\n", triTri2D(t1, t2, 0.0, true, true));
+    }
+
+    {
+        Point t1[] = { {0, 0}, {5, 0}, {0, 5} };
+        Point t2[] = { {-10, 0}, {-5, 0}, {-1, 6} };
+        printf("%d,false\n", triTri2D(t1, t2, 0.0, false, true));
+    }
+
+    {
+        Point t1[] = { {0, 0}, {5, 0}, {2.5, 5} };
+        Point t2[] = { {0, 4}, {2.5, -1}, {5, 4} };
+        printf("%d,true\n", triTri2D(t1, t2, 0.0, false, true));
+    }
+
+    {
+        Point t1[] = { {0, 0}, {1, 1}, {0, 2} };
+        Point t2[] = { {2, 1}, {3, 0}, {3, 2} };
+        printf("%d,false\n", triTri2D(t1, t2, 0.0, false, true));
+    }
+
+    {
+        Point t1[] = { {0, 0}, {1, 1}, {0, 2} };
+        Point t2[] = { {2, 1}, {3, -2}, {3, 4} };
+        printf("%d,false\n", triTri2D(t1, t2, 0.0, false, true));
+    }
+
+    //Barely touching
+    {
+        Point t1[] = { {0, 0}, {1, 0}, {0, 1} };
+        Point t2[] = { {1, 0}, {2, 0}, {1, 1} };
+        printf("%d,true\n", triTri2D(t1, t2, 0.0, false, true));
+    }
+
+    //Barely touching
+    {
+        Point t1[] = { {0, 0}, {1, 0}, {0, 1} };
+        Point t2[] = { {1, 0}, {2, 0}, {1, 1} };
+        printf("%d,false\n", triTri2D(t1, t2, 0.0, false, false));
+    }
+
+    return EXIT_SUCCESS;
+}