changed permission on func and added maximum error

made sure that not all functions were public and changed some to private
that need not be exposed.

also added in maximum error to deal with floating point inaccuracies

point.go

@@ -11,7 +11,7 @@ func distance(p1, p2 Point) float64 {
 }
 
 func onLine(rp1, rp2, p Point) bool {
-	if distance(rp1, p)+distance(rp2, p) == distance(rp1, rp2) {
+	if math.Abs(distance(rp1, p)+distance(rp2, p)-distance(rp1, rp2)) < ɛ {
 		minx, maxx := math.Min(rp1.X, rp2.X), math.Max(rp1.X, rp2.X)
 		miny, maxy := math.Min(rp1.Y, rp2.Y), math.Max(rp1.Y, rp2.Y)
 		if minx <= p.X && p.X <= maxx && miny <= p.Y && p.Y <= maxy {

rectangle.go

@@ -9,7 +9,10 @@ type Rectangle struct {
 	P1, P2, P3, P4 Point
 }
 
-func (r Rectangle) IsRect() bool {
+// maximum error used for floating point math
+var ɛ = 0.00001
+
+func (r Rectangle) isRect() bool {
 	// make sure they aren't all just the same point
 	if (r.P1.X == r.P2.X && r.P1.X == r.P3.X && r.P1.X == r.P4.X) &&
 		(r.P1.Y == r.P2.Y && r.P1.Y == r.P3.Y && r.P1.Y == r.P4.Y) {
@@ -23,39 +26,39 @@ func (r Rectangle) IsRect() bool {
 	dd2 := math.Sqrt(math.Abs(cx-r.P2.X)) + math.Sqrt(math.Abs(cy-r.P2.Y))
 	dd3 := math.Sqrt(math.Abs(cx-r.P3.X)) + math.Sqrt(math.Abs(cy-r.P3.Y))
 	dd4 := math.Sqrt(math.Abs(cx-r.P4.X)) + math.Sqrt(math.Abs(cy-r.P4.Y))
-	return dd1 == dd2 && dd1 == dd3 && dd1 == dd4
+	return math.Abs(dd1-dd2) < ɛ && math.Abs(dd1-dd3) < ɛ && math.Abs(dd1-dd4) < ɛ
 }
 
-func (r Rectangle) Neighbors(p Point) (Point, Point) {
+func (r Rectangle) neighbors(p Point) (Point, Point) {
 	keys := []float64{distance(r.P1, p), distance(r.P2, p), distance(r.P3, p), distance(r.P4, p)}
 	sort.Float64s(keys)
 	n := []Point{}
 	d := distance(r.P1, p)
-	if keys[1] == d || keys[2] == d {
+	if math.Abs(keys[1]-d) < ɛ || math.Abs(keys[2]-d) < ɛ {
 		n = append(n, r.P1)
 	}
 	d = distance(r.P2, p)
-	if keys[1] == d || keys[2] == d {
+	if math.Abs(keys[1]-d) < ɛ || math.Abs(keys[2]-d) < ɛ {
 		n = append(n, r.P2)
 	}
 	d = distance(r.P3, p)
-	if keys[1] == d || keys[2] == d {
+	if math.Abs(keys[1]-d) < ɛ || math.Abs(keys[2]-d) < ɛ {
 		n = append(n, r.P3)
 	}
 	d = distance(r.P4, p)
-	if keys[1] == d || keys[2] == d {
+	if math.Abs(keys[1]-d) < ɛ || math.Abs(keys[2]-d) < ɛ {
 		n = append(n, r.P4)
 	}
 	return n[0], n[1]
 }
 
-func (r Rectangle) Size() float64 {
-	n1, n2 := r.Neighbors(r.P1)
+func (r Rectangle) size() float64 {
+	n1, n2 := r.neighbors(r.P1)
 	return distance(r.P1, n1) * distance(r.P1, n2)
 }
 
 func (r Rectangle) inOrder() []Point {
-	n1, n2 := r.Neighbors(r.P1)
+	n1, n2 := r.neighbors(r.P1)
 	accross := &Point{}
 	if r.P2 != n1 || r.P2 != n2 {
 		accross = &r.P2
@@ -126,26 +129,26 @@ func Intersection(r1, r2 Rectangle) []Point {
 }
 
 func sumOfTri(r Rectangle, p Point) bool {
-	n1, n2 := r.Neighbors(r.P1)
+	n1, n2 := r.neighbors(r.P1)
 	x1, x2 := Point{}, Point{}
 	accross := &Point{}
 	if r.P2 != n1 || r.P2 != n2 {
 		accross = &r.P2
-		x1, x2 = r.Neighbors(r.P2)
+		x1, x2 = r.neighbors(r.P2)
 	}
 	if r.P3 != n1 || r.P3 != n2 {
 		accross = &r.P3
-		x1, x2 = r.Neighbors(r.P3)
+		x1, x2 = r.neighbors(r.P3)
 	}
 	if r.P4 != n1 || r.P4 != n2 {
 		accross = &r.P4
-		x1, x2 = r.Neighbors(r.P4)
+		x1, x2 = r.neighbors(r.P4)
 	}
-	sumTri := SizeTriangle(r.P1, n1, p) +
-		SizeTriangle(r.P1, n2, p) +
-		SizeTriangle(*accross, x1, p) +
-		SizeTriangle(*accross, x2, p)
-	if r.Size() == sumTri {
+	sumTri := sizeTriangle(r.P1, n1, p) +
+		sizeTriangle(r.P1, n2, p) +
+		sizeTriangle(*accross, x1, p) +
+		sizeTriangle(*accross, x2, p)
+	if math.Abs(r.size()-sumTri) < ɛ {
 		return true
 	}
 	return false
@@ -153,7 +156,7 @@ func sumOfTri(r Rectangle, p Point) bool {
 
 // Containment returns whether r2 is contained inside of r1
 func Containment(r1, r2 Rectangle) bool {
-	if r1.Size() <= r2.Size() {
+	if r1.size() <= r2.size() {
 		return false
 	}
 	if sumOfTri(r1, r2.P1) && sumOfTri(r1, r2.P2) && sumOfTri(r1, r2.P3) && sumOfTri(r1, r2.P4) {

triangle.go

@@ -2,6 +2,6 @@ package rect
 
 import "math"
 
-func SizeTriangle(p1, p2, p3 Point) float64 {
+func sizeTriangle(p1, p2, p3 Point) float64 {
 	return math.Abs((p1.X*p2.Y + p2.X*p3.Y + p3.X*p1.Y - p1.Y*p2.X - p2.Y*p3.X - p3.Y*p1.X) / 2)
 }

triangle_test.go

@@ -12,7 +12,7 @@ func TestSizeTriangle(t *testing.T) {
 		{[]Point{Point{10, 14}, Point{20, 15}, Point{12, 52}}, 189},
 	}
 	for _, rt := range sizeTriangleTests {
-		actual := SizeTriangle(rt.pts[0], rt.pts[1], rt.pts[2])
+		actual := sizeTriangle(rt.pts[0], rt.pts[1], rt.pts[2])
 		if actual != rt.expected {
 			t.Errorf(
 				"failed sizeTriangle:\n\texpected: %f\n\t  actual: %f",