From 46e79f21b994aa6126161cbbb0b22fcd0e6bef7a Mon Sep 17 00:00:00 2001
From: faiface <faiface@ksp.sk>
Date: Wed, 5 Jul 2017 19:35:11 +0200
Subject: [PATCH 1/4] add Rect.Area

---
 geometry.go | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/geometry.go b/geometry.go
index 503d8cb..56283a9 100644
--- a/geometry.go
+++ b/geometry.go
@@ -203,6 +203,11 @@ func (r Rect) Size() Vec {
 	return V(r.W(), r.H())
 }
 
+// Area returns the area of r. If r is not normalized, area may be negative.
+func (r Rect) Area() float64 {
+	return r.W() * r.H()
+}
+
 // Center returns the position of the center of the Rect.
 func (r Rect) Center() Vec {
 	return Lerp(r.Min, r.Max, 0.5)

From bee65f5833ae00d6c7b0f8ec2ef5cbaf275aa927 Mon Sep 17 00:00:00 2001
From: faiface <faiface@ksp.sk>
Date: Wed, 5 Jul 2017 19:51:54 +0200
Subject: [PATCH 2/4] add Rect.Intersect

---
 geometry.go | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/geometry.go b/geometry.go
index 56283a9..1c61477 100644
--- a/geometry.go
+++ b/geometry.go
@@ -160,8 +160,8 @@ type Rect struct {
 // Note that the returned rectangle is not automatically normalized.
 func R(minX, minY, maxX, maxY float64) Rect {
 	return Rect{
-		Min: V(minX, minY),
-		Max: V(maxX, maxY),
+		Min: Vec{minX, minY},
+		Max: Vec{maxX, maxY},
 	}
 }
 
@@ -257,7 +257,7 @@ func (r Rect) Contains(u Vec) bool {
 	return r.Min.X <= u.X && u.X <= r.Max.X && r.Min.Y <= u.Y && u.Y <= r.Max.Y
 }
 
-// Union returns a minimal Rect which covers both r and s. Rects r and s should be normalized.
+// Union returns the minimal Rect which covers both r and s. Rects r and s must be normalized.
 func (r Rect) Union(s Rect) Rect {
 	return R(
 		math.Min(r.Min.X, s.Min.X),
@@ -267,6 +267,20 @@ func (r Rect) Union(s Rect) Rect {
 	)
 }
 
+// Intersect returns the maximal Rect which is covered by both r and s. Rects r and s must be normalized.
+func (r Rect) Intersect(s Rect) Rect {
+	t := R(
+		math.Min(r.Max.X, s.Max.X),
+		math.Min(r.Max.Y, s.Max.Y),
+		math.Max(r.Min.X, s.Min.X),
+		math.Max(r.Min.Y, s.Min.Y),
+	)
+	if t.Min.X >= t.Max.X || t.Min.Y >= t.Max.Y {
+		return Rect{}
+	}
+	return t
+}
+
 // Matrix is a 3x2 affine matrix that can be used for all kinds of spatial transforms, such
 // as movement, scaling and rotations.
 //

From 4137f87f2206542515f6165714d785d21f865a5d Mon Sep 17 00:00:00 2001
From: faiface <faiface@ksp.sk>
Date: Wed, 5 Jul 2017 19:58:09 +0200
Subject: [PATCH 3/4] clarify Rect.Intersect doc

---
 geometry.go | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/geometry.go b/geometry.go
index 1c61477..3b2b8b3 100644
--- a/geometry.go
+++ b/geometry.go
@@ -268,6 +268,8 @@ func (r Rect) Union(s Rect) Rect {
 }
 
 // Intersect returns the maximal Rect which is covered by both r and s. Rects r and s must be normalized.
+//
+// If r and s don't overlap, this function returns R(0, 0, 0, 0).
 func (r Rect) Intersect(s Rect) Rect {
 	t := R(
 		math.Min(r.Max.X, s.Max.X),

From d7487f1f7abdc3e10098cb67cf458ca3fbb5acfd Mon Sep 17 00:00:00 2001
From: faiface <faiface@ksp.sk>
Date: Wed, 5 Jul 2017 19:51:54 +0200
Subject: [PATCH 4/4] fix Rect.Intersect

---
 geometry.go | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/geometry.go b/geometry.go
index 3b2b8b3..99514cc 100644
--- a/geometry.go
+++ b/geometry.go
@@ -272,10 +272,10 @@ func (r Rect) Union(s Rect) Rect {
 // If r and s don't overlap, this function returns R(0, 0, 0, 0).
 func (r Rect) Intersect(s Rect) Rect {
 	t := R(
-		math.Min(r.Max.X, s.Max.X),
-		math.Min(r.Max.Y, s.Max.Y),
 		math.Max(r.Min.X, s.Min.X),
 		math.Max(r.Min.Y, s.Min.Y),
+		math.Min(r.Max.X, s.Max.X),
+		math.Min(r.Max.Y, s.Max.Y),
 	)
 	if t.Min.X >= t.Max.X || t.Min.Y >= t.Max.Y {
 		return Rect{}