From 88f2a38d1a6cd318bad0e70ab3f1214418643bd4 Mon Sep 17 00:00:00 2001
From: Fraser Graham <frasergraham@me.com>
Date: Fri, 9 Aug 2013 14:49:52 -0700
Subject: [PATCH] Added dot product, cross product and intersection test

---
 govector_test.go | 65 ++++++++++++++++++++++++++++++++++++++++++++++++
 vectorpoint.go   | 18 ++++++++++++++
 2 files changed, 83 insertions(+)

diff --git a/govector_test.go b/govector_test.go
index 42d066f..bb24356 100644
--- a/govector_test.go
+++ b/govector_test.go
@@ -2,6 +2,7 @@ package govector
 
 import (
 	"fmt"
+	"math"
 	"testing"
 )
 
@@ -67,3 +68,67 @@ func TestNormalize(t *testing.T) {
 	}
 
 }
+
+func TestDot(t *testing.T) {
+	v1 := Vector2d{0, 5}
+	v2 := Vector2d{5, 0}
+	d := v1.Dot(v2)
+
+	if d != 0 {
+		t.Errorf("Dot Error")
+	}
+
+	v1 = Vector2d{1, 5}
+	v2 = Vector2d{5, 0}
+	d = v1.Dot(v2)
+
+	if d < 0 {
+		t.Errorf("Dot Error")
+	}
+
+	v1 = Vector2d{-1, 5}
+	v2 = Vector2d{5, 0}
+	d = v1.Dot(v2)
+
+	if d > 0 {
+		t.Errorf("Dot Error")
+	}
+
+	v1 = Vector2d{5, 5}
+	v2 = Vector2d{5, 0}
+	v1 = v1.Normalize()
+	v2 = v2.Normalize()
+	d = v1.Dot(v2)
+	fmt.Printf("%v\n", d)
+
+	if math.Abs(d-math.Acos(math.Pi/4)) < 0.0001 {
+		t.Errorf("Dot Error")
+	}
+}
+
+func TestIntersection(t *testing.T) {
+	p1 := Point2d{0, 5}
+	p2 := Point2d{5, 0}
+
+	v1 := Vector2d{10, 0}
+	v2 := Vector2d{0, 10}
+
+	i, p := Intersection(p1, p2, v1, v2)
+	fmt.Printf("%v %v\n", i, p)
+	if !i {
+		t.Errorf("Intersection Error")
+	}
+
+    p1 = Point2d{20, 5}
+    p2 = Point2d{5, 0}
+
+    v1 = Vector2d{10, 0}
+    v2 = Vector2d{0, 10}
+
+    i, p = Intersection(p1, p2, v1, v2)
+    fmt.Printf("%v %v\n", i, p)
+    if i {
+        t.Errorf("Intersection Error")
+    }
+
+}
diff --git a/vectorpoint.go b/vectorpoint.go
index 450323a..ccf2dcd 100644
--- a/vectorpoint.go
+++ b/vectorpoint.go
@@ -43,6 +43,24 @@ func (v Vector2d) Scale(s float64) Vector2d {
 	return Vector2d{v.X * s, v.Y * s}
 }
 
+func (v1 Vector2d) Cross(v2 Vector2d) float64 {
+	return v1.X*v2.Y - v1.Y*v2.X
+}
+
+func (v1 Vector2d) Dot(v2 Vector2d) float64 {
+	return (v1.X * v2.X) + (v1.Y * v2.Y)
+}
+
+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))
+	}
+
+	return false, Point2d{0, 0}
+}
+
 func (v Vector2d) Normalize() Vector2d {
 	if v.X == 0 && v.Y == 0 {
 		return v