Determine if two triangles overlap: Difference between revisions
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which have only a single corner in contact, if boundary points do not collide
do not overlap</pre>
=={{header|Go}}==
{{trans|Kotlin}}
<lang go>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"))
}</lang>
{{out}}
<pre>
Same as Kotlin entry.
</pre>
=={{header|Java}}==
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