gg/mx/triangle.go

package mx

import (
	"math"
	//"github.com/hajimehoshi/ebiten/v2"
)

type Triangle [3]Vector

// Returns the area of the triangle.
func (t Triangle) Area() Float {
	x1 := t[0].X
	y1 := t[0].Y
	
	x2 := t[1].X
	y2 := t[1].Y
	
	x3 := t[2].X
	y3 := t[2].Y
	
	return math.Abs(
		( x1*(y2-y3) +
			x2*(y3-y1) +
			x3*(y1-y2))/2 )
}
// Return squares of lengths of sides of the triangle.
func (t Triangle) SideLengthSquares() ([3]Float) {
	
	l1 := Line{t[0], t[1]}.LenSqr()
	l2 := Line{t[1], t[2]}.LenSqr()
	l3 := Line{t[2], t[0]}.LenSqr()
	
	return [3]Float{l1, l2, l3}
}

// Check whether the point is in the triangle.
func (t Triangle) ContainsPoint(p Vector) bool {
	d1 := Triangle{p, t[0], t[1]}.Sgn()
	d2 := Triangle{p, t[1], t[2]}.Sgn()
	d3 := Triangle{p, t[2], t[0]}.Sgn()
	
	neg := (d1 < 0) || (d2 < 0) || (d3 < 0)
	pos := (d1 > 0) || (d2 > 0) || (d3 > 0)
	
	return !(neg && pos)
}

func (t Triangle) GetContainedPoints(pts Vectors) Vectors {
	ret := make(Vectors, 0, len(pts))
	for i := range pts {
		if t.ContainsPoint(pts[i]) {
			ret = append(ret, pts[i])
		}
	}
	return ret
}

func (t Triangle) Sgn() Float {
	return (t[0].X - t[2].X) * (t[1].Y - t[2].Y)  -
		(t[1].X - t[2].X) * (t[0].Y - t[2].Y)
}

func (t Triangle) GetEdges() Lines {
	return Lines{
		Line{t[0], t[1]},
		Line{t[1], t[2]},
		Line{t[2], t[0]},
	}
}

func (t Triangle) GetVertices() Vectors {
	return Vectors{
		t[0], t[1], t[2],
	}
}

type Triangles []Triangle

func (ts Triangles) ContainsPoint(pt Vector) bool {
	for _, t := range ts {
		if t.ContainsPoint(pt) {
			return true
		}
	}
	return false
}

func (ts Triangles) GetContainedPoints(
	pts Vectors,
) Vectors {
	ret := Vectors{}
	for _, t := range ts {
		ps := t.GetContainedPoints(pts)
		ret = append(ret, ps...)
	}
	
	return ret
}

func (ts Triangles) GetVertices() Vectors {
	ret := make(Vectors, 0, len(ts)*3)
	for _, t := range ts {
		ret = append(ret, t.GetVertices()...)
	}
	return ret
}

func (ts Triangles) GetEdges() Lines {
	ret := make(Lines, 0, len(ts)*3)
	for _, t := range ts {
		ret = append(ret, t.GetEdges()...)
	}
	return ret
}