From 8a5e55e41014f69de78c586ba1095b6899aa8efd Mon Sep 17 00:00:00 2001
From: Stephen McQuay <stephen@mcquay.me>
Date: Wed, 15 Jan 2014 23:11:40 -0800
Subject: [PATCH] converted intersection to return point pointers

---
 collision.go     | 21 +++++++++++----------
 govector_test.go | 23 ++++++++++++++---------
 2 files changed, 25 insertions(+), 19 deletions(-)

diff --git a/collision.go b/collision.go
index 3edbbcd..64afe33 100644
--- a/collision.go
+++ b/collision.go
@@ -4,14 +4,15 @@ import (
 	"math"
 )
 
-func Intersection(p1, p2 Point2d, v1, v2 Vector2d) (bool, Point2d) {
+func Intersection(p1, p2 Point2d, v1, v2 Vector2d) (bool, *Point2d) {
 	t := p2.Sub(p1).Cross(v2) / v1.Cross(v2)
 	s := p2.Sub(p1).Cross(v1) / v1.Cross(v2)
 	if t > 0 && t < 1 && s > 0 && s < 1 {
-		return true, p1.Add(v1.Scale(t))
+		intersection := p1.Add(v1.Scale(t))
+		return true, &intersection
 	}
 
-	return false, Point2d{0, 0}
+	return false, nil
 }
 
 func RectRectIntersection(r1 AABB2d, r2 AABB2d) bool {
@@ -20,14 +21,14 @@ func RectRectIntersection(r1 AABB2d, r2 AABB2d) bool {
 }
 
 // returns collision, inside, point of collision
-func RectIntersection(r AABB2d, p Point2d, v Vector2d) (bool, bool, Point2d) {
+func RectIntersection(r AABB2d, p Point2d, v Vector2d) (bool, bool, *Point2d) {
 	collision := false
 	inside := false
 	start_inside := PointInRect(p, r)
 	end_inside := PointInRect(p.Add(v), r)
 	if start_inside && end_inside {
 		inside = true
-		return collision, inside, p
+		return collision, inside, nil
 	} else {
 		wall_left, col1 := Intersection(p, r.A, v, Vector2d{X: 0, Y: r.B.Y - r.A.Y})
 		if wall_left {
@@ -46,7 +47,7 @@ func RectIntersection(r AABB2d, p Point2d, v Vector2d) (bool, bool, Point2d) {
 			return wall_bottom, inside, col4
 		}
 
-		return false, false, p
+		return false, false, nil
 	}
 }
 
@@ -66,11 +67,11 @@ func ProjectPolygon(axis Vector2d, p Polygon2d) (min float32, max float32) {
 	return min, max
 }
 
-func PolygonIntersection(r Polygon2d, p Point2d, v Vector2d) (bool, Point2d) {
+func PolygonIntersection(r Polygon2d, p Point2d, v Vector2d) (bool, *Point2d) {
 	// TODO - need to test point in polygon for start and end to detect wholly
 	// inside situations
 	intersection := false
-	i_point := Point2d{}
+	var iPoint *Point2d
 	distance_sq := float32(math.MaxFloat32)
 
 	for point, _ := range r.Points {
@@ -80,13 +81,13 @@ func PolygonIntersection(r Polygon2d, p Point2d, v Vector2d) (bool, Point2d) {
 			intersection = true
 			d_sq := pt.Sub(p).MagSquared()
 			if d_sq < distance_sq {
-				i_point = pt
+				iPoint = pt
 				distance_sq = d_sq
 			}
 		}
 	}
 
-	return intersection, i_point
+	return intersection, iPoint
 }
 
 func PointInPolygon(p Point2d, py Polygon2d) bool {
diff --git a/govector_test.go b/govector_test.go
index dedf929..08bd84d 100644
--- a/govector_test.go
+++ b/govector_test.go
@@ -220,7 +220,7 @@ func TestRectIntersect(t *testing.T) {
 	type result struct {
 		collided bool
 		inside   bool
-		pos      Point2d
+		pos      *Point2d
 	}
 	tests := []struct {
 		rect     AABB2d
@@ -239,7 +239,7 @@ func TestRectIntersect(t *testing.T) {
 			expected: result{
 				collided: false,
 				inside:   true,
-				pos:      Point2d{1, 1},
+				pos:      nil,
 			},
 		},
 		// bottom
@@ -253,7 +253,7 @@ func TestRectIntersect(t *testing.T) {
 			expected: result{
 				collided: true,
 				inside:   false,
-				pos:      Point2d{10, 5},
+				pos:      &Point2d{10, 5},
 			},
 		},
 		// wall left
@@ -267,7 +267,7 @@ func TestRectIntersect(t *testing.T) {
 			expected: result{
 				collided: true,
 				inside:   false,
-				pos:      Point2d{0, 5},
+				pos:      &Point2d{0, 5},
 			},
 		},
 		// wall right
@@ -281,7 +281,7 @@ func TestRectIntersect(t *testing.T) {
 			expected: result{
 				collided: true,
 				inside:   false,
-				pos:      Point2d{10, 5},
+				pos:      &Point2d{10, 5},
 			},
 		},
 		// wall top
@@ -295,7 +295,7 @@ func TestRectIntersect(t *testing.T) {
 			expected: result{
 				collided: true,
 				inside:   false,
-				pos:      Point2d{5, 10},
+				pos:      &Point2d{5, 10},
 			},
 		},
 		// outside
@@ -309,7 +309,7 @@ func TestRectIntersect(t *testing.T) {
 			expected: result{
 				collided: false,
 				inside:   false,
-				pos:      Point2d{5, -1},
+				pos:      nil,
 			},
 		},
 	}
@@ -322,8 +322,13 @@ func TestRectIntersect(t *testing.T) {
 			t.Errorf("RectIntersection Error")
 			t.Errorf("unexpected inside: expected: %t, actual: %t", test.expected.inside, inside)
 		}
-		if pos != test.expected.pos {
-			t.Errorf("unexpected collision point: expected: %+v, actual: %+v", test.expected.pos, pos)
+		if test.expected.pos == nil && pos != nil {
+			t.Error("expected nil position, got non-nil")
+		}
+		if pos != nil && test.expected.pos != nil {
+			if *pos != *test.expected.pos {
+				t.Errorf("unexpected collision point: expected: %+v, actual: %+v", test.expected.pos, pos)
+			}
 		}
 	}