From 6170691eb1eede415640a6ac371131f00a1d70aa Mon Sep 17 00:00:00 2001
From: Fraser Graham <frasergraham@me.com>
Date: Sun, 24 Nov 2013 21:01:09 -0800
Subject: [PATCH] poly - line intersect and tests

---
 collision.go     | 18 +++++++++++++---
 govector_test.go | 54 ++++++++++++++++++++++++++++++++++++++++++++++++
 vectorpoint.go   | 10 +++++++++
 3 files changed, 79 insertions(+), 3 deletions(-)

diff --git a/collision.go b/collision.go
index eb914da..98a8ee1 100644
--- a/collision.go
+++ b/collision.go
@@ -61,9 +61,21 @@ func ProjectPolygon(axis Vector2d, p Polygon2d) (min float32, max float32) {
 	return min, max
 }
 
-func PolygonIntersection(r Polygon2d, p Point2d, v Vector2d) (bool, bool, Point2d) {
-	// TBD
-	return false, false, Point2d{}
+func PolygonIntersection(r Polygon2d, p Point2d, v Vector2d) (bool, Point2d) {
+
+	for point, _ := range r.Points {
+		if point == len(r.Points) {
+			break
+		}
+
+		edgePt, edgeVec := r.Edge(point)
+		intersection, pt := Intersection(p, edgePt, v, edgeVec)
+		if intersection {
+			return intersection, pt
+		}
+	}
+
+	return false, Point2d{}
 }
 
 func PolyPolyIntersection(p1 Polygon2d, v1 Vector2d, p2 Polygon2d, v2 Vector2d) bool {
diff --git a/govector_test.go b/govector_test.go
index 73ef614..a61fa4c 100644
--- a/govector_test.go
+++ b/govector_test.go
@@ -232,3 +232,57 @@ func TestRectIntersect(t *testing.T) {
 		t.Errorf("RectIntersection Error")
 	}
 }
+
+func TestRectRectIntersectionTrue(t *testing.T) {
+	r1 := AABB2d{Point2d{10, 10}, Point2d{20, 20}}
+	r2 := AABB2d{Point2d{15, 15}, Point2d{25, 25}}
+
+	col := RectRectIntersection(r1, r2)
+	if !col {
+		t.Errorf("RectRect Error")
+	}
+
+	r1 = AABB2d{Point2d{10, 10}, Point2d{20, 20}}
+	r2 = AABB2d{Point2d{5, 15}, Point2d{30, 25}}
+
+	col = RectRectIntersection(r1, r2)
+	if !col {
+		t.Errorf("RectRect Error")
+	}
+}
+
+func TestRectRectIntersectionFalse(t *testing.T) {
+	r1 := AABB2d{Point2d{10, 10}, Point2d{14, 14}}
+	r2 := AABB2d{Point2d{15, 15}, Point2d{25, 25}}
+
+	col := RectRectIntersection(r1, r2)
+	if col {
+		t.Errorf("RectRect Error")
+	}
+}
+
+func TestPolyIntersect(t *testing.T) {
+	p1 := Polygon2d{}
+	p1.Points = append(p1.Points, Vector2d{3, 3})
+	p1.Points = append(p1.Points, Vector2d{5, 5})
+	p1.Points = append(p1.Points, Vector2d{5, 3})
+
+	i, p := PolygonIntersection(p1, Point2d{0, 0}, Vector2d{10, 10})
+	if i {
+		fmt.Printf("%v", p)
+		t.Errorf("PolyIntersect Error")
+	}
+}
+
+func TestPolyIntersectFail(t *testing.T) {
+	p1 := Polygon2d{}
+	p1.Points = append(p1.Points, Vector2d{3, 3})
+	p1.Points = append(p1.Points, Vector2d{5, 5})
+	p1.Points = append(p1.Points, Vector2d{5, 3})
+
+	i, p := PolygonIntersection(p1, Point2d{0, 0}, Vector2d{-10, -10})
+	if i {
+		fmt.Printf("%v", p)
+		t.Errorf("PolyIntersect Error")
+	}
+}
diff --git a/vectorpoint.go b/vectorpoint.go
index e559d15..23a3454 100644
--- a/vectorpoint.go
+++ b/vectorpoint.go
@@ -15,6 +15,16 @@ type Polygon2d struct {
 	Origin  Point2d    `json:"origin"`
 }
 
+func (p Polygon2d) Edge(i int) (Point2d, Vector2d) {
+	if i >= len(p.Points)-1 {
+		return Point2d{}, Vector2d{}
+	}
+
+	p1 := p.Origin.Add(p.Points[i])
+	p2 := p.Origin.Add(p.Points[i+1])
+	return p1, p2.Sub(p1)
+}
+
 type Vector2d struct {
 	X float32 `json:"x"`
 	Y float32 `json:"y"`