Determine if two triangles overlap: Difference between revisions

Content added Content deleted

Inline

@@ Line 6,008: / Line 6,008: @@
 which have only a single corner in contact, if boundary points do not collide
 do not overlap</pre>
+=={{header|Vlang}}==
+{{trans|Go}}
+<lang vlang>struct Point {
+    x f64
+	y f64
+}
+fn (p Point) str() string {
+    return "(${p.x:.1f}, ${p.y:.1f})"
+}
+struct Triangle {
+mut:
+    p1 Point
+	p2 Point
+	p3 Point
+}
+fn (t Triangle) str() string {
+    return "Triangle $t.p1, $t.p2, $t.p3"
+}
+fn (t Triangle) det_2d() f64 {
+    return t.p1.x * (t.p2.y - t.p3.y) +
+           t.p2.x * (t.p3.y - t.p1.y) +
+           t.p3.x * (t.p1.y - t.p2.y)
+}
+fn (mut t Triangle) check_tri_winding(allow_reversed bool) {
+    det_tri := t.det_2d()
+    if det_tri < 0.0 {
+        if allow_reversed {
+            a := t.p3
+            t.p3 = t.p2
+            t.p2 = a
+        } else {
+            panic("Triangle has wrong winding direction.")
+        }
+    }
+}
+fn boundary_collide_chk(t Triangle, eps f64, does bool) bool {
+	if does {
+    	return t.det_2d() < eps
+	}
+	return t.det_2d() <= eps
+}
+fn tri_tri_2d(mut t1 Triangle, mut t2 Triangle, eps f64, allow_reversed bool, on_boundary bool) bool {
+    // Triangles must be expressed anti-clockwise.
+    t1.check_tri_winding(allow_reversed)
+    t2.check_tri_winding(allow_reversed)
+    lp1 := [t1.p1, t1.p2, t1.p3]
+    lp2 := [t2.p1, t2.p2, t2.p3]
+    // for each edge E of t1
+    for i in 0..3 {
+        j := (i + 1) % 3
+        // Check all Points of t2 lay on the external side of edge E.
+        // If they do, the Triangles do not overlap.
+        tri1 := Triangle{lp1[i], lp1[j], lp2[0]}
+        tri2 := Triangle{lp1[i], lp1[j], lp2[1]}
+        tri3 := Triangle{lp1[i], lp1[j], lp2[2]}
+        if boundary_collide_chk(tri1, eps,on_boundary) && boundary_collide_chk(tri2, eps,on_boundary) && boundary_collide_chk(tri3, eps,on_boundary) {
+            return false
+        }
+    }
+    // for each edge E of t2
+    for i in 0..3 {
+        j := (i + 1) % 3
+        // Check all Points of t1 lay on the external side of edge E.
+        // If they do, the Triangles do not overlap.
+        tri1 := Triangle{lp2[i], lp2[j], lp1[0]}
+        tri2 := Triangle{lp2[i], lp2[j], lp1[1]}
+        tri3 := Triangle{lp2[i], lp2[j], lp1[2]}
+        if boundary_collide_chk(tri1, eps,on_boundary) && boundary_collide_chk(tri2, eps,on_boundary) && boundary_collide_chk(tri3, eps,on_boundary) {
+            return false
+        }
+    }
+    // The Triangles overlap.
+    return true
+}
+fn iff(cond bool, s1 string, s2 string) string {
+    if cond {
+        return s1
+    }
+    return s2
+}
+fn main() {
+    mut t1 := Triangle{Point{0.0, 0.0}, Point{5.0, 0.0}, Point{0.0, 5.0}}
+    mut t2 := Triangle{Point{0.0, 0.0}, Point{5.0, 0.0}, Point{0.0, 6.0}}
+    println("\n$t1 and\n$t2")
+    mut overlapping := tri_tri_2d(mut t1, mut t2, 0.0, false, true)
+    println(iff(overlapping, "overlap", "do not overlap"))
+    // Need to allow reversed for this pair to avoid panic.
+    t1 = Triangle{Point{0.0, 0.0}, Point{0.0, 5.0}, Point{5.0, 0.0}}
+    t2 = t1
+    println("\n$t1 and\n$t2")
+    overlapping = tri_tri_2d(mut t1, mut t2, 0.0, true, true)
+    println(iff(overlapping, "overlap (reversed)", "do not overlap"))
+    t1 = Triangle{Point{0.0, 0.0}, Point{5.0, 0.0}, Point{0.0, 5.0}}
+    t2 = Triangle{Point{-10.0, 0.0}, Point{-5.0, 0.0}, Point{-1.0, 6.0}}
+    println("\n$t1 and\n$t2")
+    overlapping = tri_tri_2d(mut t1, mut t2, 0.0, false, true)
+    println(iff(overlapping, "overlap", "do not overlap"))
+    t1.p3 = Point{2.5, 5.0}
+    t2 = Triangle{Point{0.0, 4.0}, Point{2.5, -1.0}, Point{5.0, 4.0}}
+    println("\n$t1 and\n$t2")
+    overlapping = tri_tri_2d(mut t1, mut t2, 0.0, false, true)
+    println(iff(overlapping, "overlap", "do not overlap"))
+    t1 = Triangle{Point{0.0, 0.0}, Point{1.0, 1.0}, Point{0.0, 2.0}}
+    t2 = Triangle{Point{2.0, 1.0}, Point{3.0, 0.0}, Point{3.0, 2.0}}
+    println("\n$t1 and\n$t2")
+    overlapping = tri_tri_2d(mut t1, mut t2, 0.0, false, true)
+    println(iff(overlapping, "overlap", "do not overlap"))
+    t2 = Triangle{Point{2.0, 1.0}, Point{3.0, -2.0}, Point{3.0, 4.0}}
+    println("\n$t1 and\n$t2")
+    overlapping = tri_tri_2d(mut t1, mut t2, 0.0, false, true)
+    println(iff(overlapping, "overlap", "do not overlap"))
+    t1 = Triangle{Point{0.0, 0.0}, Point{1.0, 0.0}, Point{0.0, 1.0}}
+    t2 = Triangle{Point{1.0, 0.0}, Point{2.0, 0.0}, Point{1.0, 1.1}}
+    println("\n$t1 and\n$t2")
+    println("which have only a single corner in contact, if boundary Points collide")
+    overlapping = tri_tri_2d(mut t1, mut t2, 0.0, false, true)
+    println(iff(overlapping, "overlap", "do not overlap"))
+    println("\n$t1 and\n$t2")
+    println("which have only a single corner in contact, if boundary Points do not collide")
+    overlapping = tri_tri_2d(mut t1, mut t2, 0.0, false, false)
+    println(iff(overlapping, "overlap", "do not overlap"))
+}</lang>
+{{out}}
+<pre>Same as Kotlin Entry</pre>
 =={{header|Wren}}==