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Source file src/image/geom.go

Documentation: image

  // 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 (
  	"image/color"
  	"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 reports 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 reports whether p and q are equal.
  func (p Point) Eq(q Point) bool {
  	return p == q
  }
  
  // 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.
  //
  // A Rectangle is also an Image whose bounds are the rectangle itself. At
  // returns color.Opaque for points in the rectangle and color.Transparent
  // otherwise.
  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},
  	}
  }
  
  // Sub 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.Empty() {
  		return s
  	}
  	if s.Empty() {
  		return r
  	}
  	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 reports 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 reports whether r and s contain the same set of points. All empty
  // rectangles are considered equal.
  func (r Rectangle) Eq(s Rectangle) bool {
  	return r == s || r.Empty() && s.Empty()
  }
  
  // Overlaps reports whether r and s have a non-empty intersection.
  func (r Rectangle) Overlaps(s Rectangle) bool {
  	return !r.Empty() && !s.Empty() &&
  		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 reports 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
  }
  
  // At implements the Image interface.
  func (r Rectangle) At(x, y int) color.Color {
  	if (Point{x, y}).In(r) {
  		return color.Opaque
  	}
  	return color.Transparent
  }
  
  // Bounds implements the Image interface.
  func (r Rectangle) Bounds() Rectangle {
  	return r
  }
  
  // ColorModel implements the Image interface.
  func (r Rectangle) ColorModel() color.Model {
  	return color.Alpha16Model
  }
  
  // ZR is the zero Rectangle.
  var ZR Rectangle
  
  // Rect is shorthand for Rectangle{Pt(x0, y0), Pt(x1, y1)}. The returned
  // rectangle has minimum and maximum coordinates swapped if necessary so that
  // it is well-formed.
  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}}
  }
  

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