| // Copyright ©2022 The Gonum 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 r2 |
| |
| import "math" |
| |
| // Box is a 2D bounding box. Well formed Boxes have |
| // Min components smaller than Max components. |
| type Box struct { |
| Min, Max Vec |
| } |
| |
| // NewBox is shorthand for Box{Min:Vec{x0,y0}, Max:Vec{x1,y1}}. |
| // The sides are swapped so that the resulting Box is well formed. |
| func NewBox(x0, y0, x1, y1 float64) Box { |
| return Box{ |
| Min: Vec{X: math.Min(x0, x1), Y: math.Min(y0, y1)}, |
| Max: Vec{X: math.Max(x0, x1), Y: math.Max(y0, y1)}, |
| } |
| } |
| |
| // Size returns the size of the Box. |
| func (a Box) Size() Vec { |
| return Sub(a.Max, a.Min) |
| } |
| |
| // Center returns the center of the Box. |
| func (a Box) Center() Vec { |
| return Scale(0.5, Add(a.Min, a.Max)) |
| } |
| |
| // Empty returns true if a Box's volume is zero |
| // or if a Min component is greater than its Max component. |
| func (a Box) Empty() bool { |
| return a.Min.X >= a.Max.X || a.Min.Y >= a.Max.Y |
| } |
| |
| // Vertices returns a slice of the 4 vertices |
| // corresponding to each of the Box's corners. |
| // |
| // The order of the vertices is CCW in the XY plane starting at the box minimum. |
| // If viewing box from +Z position the ordering is as follows: |
| // 1. Bottom left. |
| // 2. Bottom right. |
| // 3. Top right. |
| // 4. Top left. |
| func (a Box) Vertices() []Vec { |
| return []Vec{ |
| 0: a.Min, |
| 1: {a.Max.X, a.Min.Y}, |
| 2: a.Max, |
| 3: {a.Min.X, a.Max.Y}, |
| } |
| } |
| |
| // Union returns a box enclosing both the receiver and argument Boxes. |
| func (a Box) Union(b Box) Box { |
| if a.Empty() { |
| return b |
| } |
| if b.Empty() { |
| return a |
| } |
| return Box{ |
| Min: minElem(a.Min, b.Min), |
| Max: maxElem(a.Max, b.Max), |
| } |
| } |
| |
| // Add adds v to the bounding box components. |
| // It is the equivalent of translating the Box by v. |
| func (a Box) Add(v Vec) Box { |
| return Box{Add(a.Min, v), Add(a.Max, v)} |
| } |
| |
| // Scale returns a new Box scaled by a size vector around its center. |
| // The scaling is done element wise, which is to say the Box's X size is |
| // scaled by v.X. Negative components of v are interpreted as zero. |
| func (a Box) Scale(v Vec) Box { |
| v = maxElem(v, Vec{}) |
| // TODO(soypat): Probably a better way to do this. |
| return centeredBox(a.Center(), mulElem(v, a.Size())) |
| } |
| |
| // centeredBox creates a Box with a given center and size. Size's negative |
| // components are interpreted as zero so that resulting box is well formed. |
| func centeredBox(center, size Vec) Box { |
| size = maxElem(size, Vec{}) |
| half := Scale(0.5, absElem(size)) |
| return Box{Min: Sub(center, half), Max: Add(center, half)} |
| } |
| |
| // Contains returns true if v is contained within the bounds of the Box. |
| func (a Box) Contains(v Vec) bool { |
| if a.Empty() { |
| return v == a.Min && v == a.Max |
| } |
| return a.Min.X <= v.X && v.X <= a.Max.X && |
| a.Min.Y <= v.Y && v.Y <= a.Max.Y |
| } |
| |
| // Canon returns the canonical version of b. The returned Box has minimum |
| // and maximum coordinates swapped if necessary so that it is well-formed. |
| func (b Box) Canon() Box { |
| return Box{ |
| Min: minElem(b.Min, b.Max), |
| Max: maxElem(b.Min, b.Max), |
| } |
| } |