Data commit

Task/Determine-if-two-triangles-overlap/Go/determine-if-two-triangles-overlap.go

@@ -0,0 +1,148 @@
+package main
+
+import "fmt"
+
+type point struct {
+    x, y float64
+}
+
+func (p point) String() string {
+    return fmt.Sprintf("(%.1f, %.1f)", p.x, p.y)
+}
+
+type triangle struct {
+    p1, p2, p3 point
+}
+
+func (t *triangle) String() string {
+    return fmt.Sprintf("Triangle %s, %s, %s", t.p1, t.p2, t.p3)
+}
+
+func (t *triangle) det2D() float64 {
+    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)
+}
+
+func (t *triangle) checkTriWinding(allowReversed bool) {
+    detTri := t.det2D()
+    if detTri < 0.0 {
+        if allowReversed {
+            a := t.p3
+            t.p3 = t.p2
+            t.p2 = a
+        } else {
+            panic("Triangle has wrong winding direction.")
+        }
+    }
+}
+
+func boundaryCollideChk(t *triangle, eps float64) bool {
+    return t.det2D() < eps
+}
+
+func boundaryDoesntCollideChk(t *triangle, eps float64) bool {
+    return t.det2D() <= eps
+}
+
+func triTri2D(t1, t2 *triangle, eps float64, allowReversed, onBoundary bool) bool {
+    // Triangles must be expressed anti-clockwise.
+    t1.checkTriWinding(allowReversed)
+    t2.checkTriWinding(allowReversed)
+
+    // 'onBoundary' determines whether points on boundary are considered as colliding or not.
+    var chkEdge func (*triangle, float64) bool
+    if onBoundary {
+        chkEdge = boundaryCollideChk
+    } else {
+        chkEdge = boundaryDoesntCollideChk
+    }
+    lp1 := [3]point{t1.p1, t1.p2, t1.p3}
+    lp2 := [3]point{t2.p1, t2.p2, t2.p3}
+
+    // for each edge E of t1
+    for i := 0; i < 3; i++ {
+        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 chkEdge(tri1, eps) && chkEdge(tri2, eps) && chkEdge(tri3, eps) {
+            return false
+        }
+    }
+
+    // for each edge E of t2
+    for i := 0; i < 3; i++ {
+        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 chkEdge(tri1, eps) && chkEdge(tri2, eps) && chkEdge(tri3, eps) {
+            return false
+        }
+    }
+
+    // The triangles overlap.
+    return true
+}
+
+func iff(cond bool, s1, s2 string) string {
+    if cond {
+        return s1
+    }
+    return s2
+}
+
+func main() {
+    t1 := &triangle{point{0.0, 0.0}, point{5.0, 0.0}, point{0.0, 5.0}}
+    t2 := &triangle{point{0.0, 0.0}, point{5.0, 0.0}, point{0.0, 6.0}}
+    fmt.Printf("%s and\n%s\n", t1, t2)
+    overlapping := triTri2D(t1, t2, 0.0, false, true)
+    fmt.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
+    fmt.Printf("\n%s and\n%s\n", t1, t2)
+    overlapping = triTri2D(t1, t2, 0.0, true, true)
+    fmt.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}}
+    fmt.Printf("\n%s and\n%s\n", t1, t2)
+    overlapping = triTri2D(t1, t2, 0.0, false, true)
+    fmt.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}}
+    fmt.Printf("\n%s and\n%s\n", t1, t2)
+    overlapping = triTri2D(t1, t2, 0.0, false, true)
+    fmt.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}}
+    fmt.Printf("\n%s and\n%s\n", t1, t2)
+    overlapping = triTri2D(t1, t2, 0.0, false, true)
+    fmt.Println(iff(overlapping, "overlap", "do not overlap"))
+
+    t2 = &triangle{point{2.0, 1.0}, point{3.0, -2.0}, point{3.0, 4.0}}
+    fmt.Printf("\n%s and\n%s\n", t1, t2)
+    overlapping = triTri2D(t1, t2, 0.0, false, true)
+    fmt.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}}
+    fmt.Printf("\n%s and\n%s\n", t1, t2)
+    println("which have only a single corner in contact, if boundary points collide")
+    overlapping = triTri2D(t1, t2, 0.0, false, true)
+    fmt.Println(iff(overlapping, "overlap", "do not overlap"))
+
+    fmt.Printf("\n%s and\n%s\n", t1, t2)
+    fmt.Println("which have only a single corner in contact, if boundary points do not collide")
+    overlapping = triTri2D(t1, t2, 0.0, false, false)
+    fmt.Println(iff(overlapping, "overlap", "do not overlap"))
+}