/
polygon.go
244 lines (213 loc) · 5.73 KB
/
polygon.go
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package render
import (
"errors"
"image"
"image/color"
"math"
"github.com/oakmound/oak/physics"
)
// A Rect is a helper type storing X1,Y1,X2,Y2 in floats
type Rect struct {
MinX, MaxX, MinY, MaxY float64
}
// A Polygon is a renderable that is represented by a set of in order points
// on a plane.
type Polygon struct {
*Sprite
Rect
points []physics.Vector
}
// ScreenPolygon returns a polygon on the screen, used for draw polygons.
func ScreenPolygon(points []physics.Vector, w, h int) (*Polygon, error) {
if len(points) < 3 {
return nil, errors.New("Please give at least three points to NewPolygon calls")
}
MinX, MinY, MaxX, MaxY, _, _ := BoundingRect(points)
rect := image.Rect(0, 0, w, h)
rgba := image.NewRGBA(rect)
return &Polygon{
Sprite: NewSprite(0, 0, rgba),
Rect: Rect{
MinX: MinX,
MinY: MinY,
MaxX: MaxX,
MaxY: MaxY,
},
points: points,
}, nil
}
// NewPolygon takes in a set of points and returns a polygon. If less than three
// points are provided, this fails.
func NewPolygon(points []physics.Vector) (*Polygon, error) {
if len(points) < 3 {
return nil, errors.New("Please give at least three points to NewPolygon calls")
}
// Calculate the bounding rectangle of the polygon by
// finding the maximum and minimum x and y values of the given points
MinX, MinY, MaxX, MaxY, w, h := BoundingRect(points)
rect := image.Rect(0, 0, w, h)
rgba := image.NewRGBA(rect)
return &Polygon{
Sprite: NewSprite(MinX, MinY, rgba),
Rect: Rect{
MinX: MinX,
MinY: MinY,
MaxX: MaxX,
MaxY: MaxY,
},
points: points,
}, nil
}
// UpdatePoints resets the points of this polygon to be the passed in points
func (pg *Polygon) UpdatePoints(points []physics.Vector) {
pg.points = points
pg.MinX, pg.MinY, pg.MaxX, pg.MaxY, _, _ = BoundingRect(points)
}
// Fill fills the inside of this polygon with the input color
func (pg *Polygon) Fill(c color.Color) {
// Reset the rgba of the polygon
bounds := pg.r.Bounds()
rect := image.Rect(0, 0, bounds.Max.X, bounds.Max.Y)
rgba := image.NewRGBA(rect)
minx := pg.Rect.MinX
miny := pg.Rect.MinY
for x := 0; x < bounds.Max.X; x++ {
for y := 0; y < bounds.Max.Y; y++ {
if pg.Contains(float64(x)+minx, float64(y)+miny) {
rgba.Set(x, y, c)
}
}
}
pg.r = rgba
}
// GetOutline returns a set of lines of the given color along this polygon's outline
func (pg *Polygon) GetOutline(c color.Color) *Composite {
sl := NewComposite([]Modifiable{})
j := len(pg.points) - 1
for i, p2 := range pg.points {
p1 := pg.points[j]
MinX := math.Min(p1.X(), p2.X())
MinY := math.Min(p1.Y(), p2.Y())
sl.AppendOffset(NewLine(p1.X(), p1.Y(), p2.X(), p2.Y(), c), physics.NewVector(MinX, MinY))
j = i
}
return sl
}
// FillInverse colors this polygon's exterior the given color
func (pg *Polygon) FillInverse(c color.Color) {
bounds := pg.r.Bounds()
rect := image.Rect(0, 0, bounds.Max.X, bounds.Max.Y)
rgba := image.NewRGBA(rect)
for x := 0; x < bounds.Max.X; x++ {
for y := 0; y < bounds.Max.Y; y++ {
if !pg.ConvexContains(float64(x), float64(y)) {
rgba.Set(x, y, c)
}
}
}
pg.r = rgba
}
// BoundingRect converts a set of points into their minimum bounding rectangle
func BoundingRect(points []physics.Vector) (MinX, MinY, MaxX, MaxY float64, w, h int) {
MinX = math.MaxFloat64
MinY = math.MaxFloat64
MaxX = MinX * -1
MaxY = MinY * -1
for _, p := range points {
x := p.X()
y := p.Y()
if x < MinX {
MinX = x
}
if x > MaxX {
MaxX = x
}
if y < MinY {
MinY = y
}
if y > MaxY {
MaxY = y
}
}
w = int(MaxX - MinX)
h = int(MaxY - MinY)
return
}
// Contains returns whether or not the current Polygon contains the passed in Point.
// It is the default containment function, versus wrapping and convex.
func (pg *Polygon) Contains(x, y float64) (contains bool) {
if x < pg.MinX || x > pg.MaxX || y < pg.MinY || y > pg.MaxY {
return
}
j := len(pg.points) - 1
for i := 0; i < len(pg.points); i++ {
tp1 := pg.points[i]
tp2 := pg.points[j]
if (tp1.Y() > y) != (tp2.Y() > y) { // Three comparisons
if x < (tp2.X()-tp1.X())*(y-tp1.Y())/(tp2.Y()-tp1.Y())+tp1.X() { // One Comparison, Four add/sub, Two mult/div
contains = !contains
}
}
j = i
}
return
}
// WrappingContains returns whether the given point is contained by the input polygon.
func (pg *Polygon) WrappingContains(x, y float64) bool {
if x < pg.MinX || x > pg.MaxX || y < pg.MinY || y > pg.MaxY {
return false
}
wn := 0
j := len(pg.points) - 1
for i := 0; i < len(pg.points); i++ {
tp1 := pg.points[i]
tp2 := pg.points[j]
if tp1.Y() <= y && tp2.Y() > y && isLeft(tp1, tp2, x, y) > 0 { // Three comparison, Five add/sub, Two mult/div
wn++
}
if tp2.Y() >= y && isLeft(tp1, tp2, x, y) < 0 { // Two Comparison, Five add/sub, Two mult/div
wn--
}
j = i
}
return wn == 0
}
// ConvexContains returns whether the given point is contained by the input polygon.
// It assumes the polygon is convex. It outperforms the alternatives.
func (pg *Polygon) ConvexContains(x, y float64) bool {
if x < pg.MinX || x > pg.MaxX || y < pg.MinY || y > pg.MaxY {
return false
}
prev := 0
for i := 0; i < len(pg.points); i++ {
tp1 := pg.points[i]
tp2 := pg.points[(i+1)%len(pg.points)]
tp3 := vSub(tp2, tp1)
tp4 := vSub(physics.NewVector(x, y), tp1)
cur := getSide(tp3, tp4)
if cur == 0 {
return false
} else if prev == 0 {
} else if prev != cur {
return false
}
prev = cur
}
return true
}
func getSide(a, b physics.Vector) int {
x := a.X()*b.Y() - a.Y()*b.X()
if x == 0 {
return 0
} else if x < 1 {
return -1
} else {
return 1
}
}
func vSub(a, b physics.Vector) physics.Vector {
return physics.NewVector(a.X()-b.X(), a.Y()-b.Y())
}
func isLeft(p1, p2 physics.Vector, x, y float64) float64 {
return (p1.X()-x)*(p2.Y()-y) - (p2.X()-x)*(p1.Y()-y)
}