1 files changed, 234 insertions, 0 deletions
diff --git a/src/pkg/image/geom.go b/src/pkg/image/geom.go
new file mode 100644
index 000000000..667aee625
--- /dev/null
+++ b/src/pkg/image/geom.go
@@ -0,0 +1,234 @@
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package image
+
+import (
+	"strconv"
+)
+
+// A Point is an X, Y coordinate pair. The axes increase right and down.
+type Point struct {
+	X, Y int
+}
+
+// String returns a string representation of p like "(3,4)".
+func (p Point) String() string {
+	return "(" + strconv.Itoa(p.X) + "," + strconv.Itoa(p.Y) + ")"
+}
+
+// Add returns the vector p+q.
+func (p Point) Add(q Point) Point {
+	return Point{p.X + q.X, p.Y + q.Y}
+}
+
+// Sub returns the vector p-q.
+func (p Point) Sub(q Point) Point {
+	return Point{p.X - q.X, p.Y - q.Y}
+}
+
+// Mul returns the vector p*k.
+func (p Point) Mul(k int) Point {
+	return Point{p.X * k, p.Y * k}
+}
+
+// Div returns the vector p/k.
+func (p Point) Div(k int) Point {
+	return Point{p.X / k, p.Y / k}
+}
+
+// In returns whether p is in r.
+func (p Point) In(r Rectangle) bool {
+	return r.Min.X <= p.X && p.X < r.Max.X &&
+		r.Min.Y <= p.Y && p.Y < r.Max.Y
+}
+
+// Mod returns the point q in r such that p.X-q.X is a multiple of r's width
+// and p.Y-q.Y is a multiple of r's height.
+func (p Point) Mod(r Rectangle) Point {
+	w, h := r.Dx(), r.Dy()
+	p = p.Sub(r.Min)
+	p.X = p.X % w
+	if p.X < 0 {
+		p.X += w
+	}
+	p.Y = p.Y % h
+	if p.Y < 0 {
+		p.Y += h
+	}
+	return p.Add(r.Min)
+}
+
+// Eq returns whether p and q are equal.
+func (p Point) Eq(q Point) bool {
+	return p.X == q.X && p.Y == q.Y
+}
+
+// ZP is the zero Point.
+var ZP Point
+
+// Pt is shorthand for Point{X, Y}.
+func Pt(X, Y int) Point {
+	return Point{X, Y}
+}
+
+// A Rectangle contains the points with Min.X <= X < Max.X, Min.Y <= Y < Max.Y.
+// It is well-formed if Min.X <= Max.X and likewise for Y. Points are always
+// well-formed. A rectangle's methods always return well-formed outputs for
+// well-formed inputs.
+type Rectangle struct {
+	Min, Max Point
+}
+
+// String returns a string representation of r like "(3,4)-(6,5)".
+func (r Rectangle) String() string {
+	return r.Min.String() + "-" + r.Max.String()
+}
+
+// Dx returns r's width.
+func (r Rectangle) Dx() int {
+	return r.Max.X - r.Min.X
+}
+
+// Dy returns r's height.
+func (r Rectangle) Dy() int {
+	return r.Max.Y - r.Min.Y
+}
+
+// Size returns r's width and height.
+func (r Rectangle) Size() Point {
+	return Point{
+		r.Max.X - r.Min.X,
+		r.Max.Y - r.Min.Y,
+	}
+}
+
+// Add returns the rectangle r translated by p.
+func (r Rectangle) Add(p Point) Rectangle {
+	return Rectangle{
+		Point{r.Min.X + p.X, r.Min.Y + p.Y},
+		Point{r.Max.X + p.X, r.Max.Y + p.Y},
+	}
+}
+
+// Add returns the rectangle r translated by -p.
+func (r Rectangle) Sub(p Point) Rectangle {
+	return Rectangle{
+		Point{r.Min.X - p.X, r.Min.Y - p.Y},
+		Point{r.Max.X - p.X, r.Max.Y - p.Y},
+	}
+}
+
+// Inset returns the rectangle r inset by n, which may be negative. If either
+// of r's dimensions is less than 2*n then an empty rectangle near the center
+// of r will be returned.
+func (r Rectangle) Inset(n int) Rectangle {
+	if r.Dx() < 2*n {
+		r.Min.X = (r.Min.X + r.Max.X) / 2
+		r.Max.X = r.Min.X
+	} else {
+		r.Min.X += n
+		r.Max.X -= n
+	}
+	if r.Dy() < 2*n {
+		r.Min.Y = (r.Min.Y + r.Max.Y) / 2
+		r.Max.Y = r.Min.Y
+	} else {
+		r.Min.Y += n
+		r.Max.Y -= n
+	}
+	return r
+}
+
+// Intersect returns the largest rectangle contained by both r and s. If the
+// two rectangles do not overlap then the zero rectangle will be returned.
+func (r Rectangle) Intersect(s Rectangle) Rectangle {
+	if r.Min.X < s.Min.X {
+		r.Min.X = s.Min.X
+	}
+	if r.Min.Y < s.Min.Y {
+		r.Min.Y = s.Min.Y
+	}
+	if r.Max.X > s.Max.X {
+		r.Max.X = s.Max.X
+	}
+	if r.Max.Y > s.Max.Y {
+		r.Max.Y = s.Max.Y
+	}
+	if r.Min.X > r.Max.X || r.Min.Y > r.Max.Y {
+		return ZR
+	}
+	return r
+}
+
+// Union returns the smallest rectangle that contains both r and s.
+func (r Rectangle) Union(s Rectangle) Rectangle {
+	if r.Min.X > s.Min.X {
+		r.Min.X = s.Min.X
+	}
+	if r.Min.Y > s.Min.Y {
+		r.Min.Y = s.Min.Y
+	}
+	if r.Max.X < s.Max.X {
+		r.Max.X = s.Max.X
+	}
+	if r.Max.Y < s.Max.Y {
+		r.Max.Y = s.Max.Y
+	}
+	return r
+}
+
+// Empty returns whether the rectangle contains no points.
+func (r Rectangle) Empty() bool {
+	return r.Min.X >= r.Max.X || r.Min.Y >= r.Max.Y
+}
+
+// Eq returns whether r and s are equal.
+func (r Rectangle) Eq(s Rectangle) bool {
+	return r.Min.X == s.Min.X && r.Min.Y == s.Min.Y &&
+		r.Max.X == s.Max.X && r.Max.Y == s.Max.Y
+}
+
+// Overlaps returns whether r and s have a non-empty intersection.
+func (r Rectangle) Overlaps(s Rectangle) bool {
+	return r.Min.X < s.Max.X && s.Min.X < r.Max.X &&
+		r.Min.Y < s.Max.Y && s.Min.Y < r.Max.Y
+}
+
+// In returns whether every point in r is in s.
+func (r Rectangle) In(s Rectangle) bool {
+	if r.Empty() {
+		return true
+	}
+	// Note that r.Max is an exclusive bound for r, so that r.In(s)
+	// does not require that r.Max.In(s).
+	return s.Min.X <= r.Min.X && r.Max.X <= s.Max.X &&
+		s.Min.Y <= r.Min.Y && r.Max.Y <= s.Max.Y
+}
+
+// Canon returns the canonical version of r. The returned rectangle has minimum
+// and maximum coordinates swapped if necessary so that it is well-formed.
+func (r Rectangle) Canon() Rectangle {
+	if r.Max.X < r.Min.X {
+		r.Min.X, r.Max.X = r.Max.X, r.Min.X
+	}
+	if r.Max.Y < r.Min.Y {
+		r.Min.Y, r.Max.Y = r.Max.Y, r.Min.Y
+	}
+	return r
+}
+
+// ZR is the zero Rectangle.
+var ZR Rectangle
+
+// Rect is shorthand for Rectangle{Pt(x0, y0), Pt(x1, y1)}.
+func Rect(x0, y0, x1, y1 int) Rectangle {
+	if x0 > x1 {
+		x0, x1 = x1, x0
+	}
+	if y0 > y1 {
+		y0, y1 = y1, y0
+	}
+	return Rectangle{Point{x0, y0}, Point{x1, y1}}
+}