gg/triangle.go

package gg

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

type EVertex = ebiten.Vertex

// Ebitens vector in better abstractions like Vectors.
type Vertex struct {
	Dst Vector
	Src Vector
	Colority
}

type Triangle [3]Vector
type DrawableTriangles struct {
	Triangles
	Colority
}

func (v Vertex) Ebiten() EVertex {
	return EVertex {
		DstX: float32(v.Dst.X),
		DstY: float32(v.Dst.Y),
		SrcX: float32(v.Src.X),
		SrcY: float32(v.Src.Y),
		ColorR: float32(v.Color.R)/(float32(MaxColorV)),
		ColorG: float32(v.Color.G)/(float32(MaxColorV)),
		ColorB: float32(v.Color.B)/(float32(MaxColorV)),
		ColorA: float32(v.Color.A)/(float32(MaxColorV)),
	}
}

// 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)
}
func sqr(v Float) Float {
	return v * v
}
// Return squares of lengths of sides of the triangle.
func (t Triangle) SideLengthSquares() ([3]Float) {
	
	l1 := Edge{t[0], t[1]}.LenSqr()
	l2 := Edge{t[1], t[2]}.LenSqr()
	l3 := Edge{t[2], t[0]}.LenSqr()
	
	return [3]Float{l1, l2, l3}
}

// Check whether the point is in the triangle.
func (t Triangle) ContainsPoint(p Point) 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) ContainedPoints(pts Points) []Point {
	ret := []Point{}
	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) Vertices() Vertices {
	return Vertices{
		t[0], t[1], t[2],
	}
}
type Triangles []Triangle

func (ts Triangles) ContainedPoints(pts Points) (Points) {
	ret := []Point{}
	for _, t := range ts {
		ps := t.ContainedPoints(pts)
		ret = append(ret, ps...)
	}
	
	return ret
}

func (r *DrawableTriangles) MakeEVertices(c *Context) []EVertex {
	m := c.Camera.RealMatrix()
	vs := make([]ebiten.Vertex, len(r.Triangles) * 3)
	var buf Vertex
	buf.Color = r.Color
	for i := range r.Triangles {
		for j := range r.Triangles[i] {
			buf.Dst = r.Triangles[i][j].Apply(m)
			vs[i*3 + j] = buf.Ebiten()
		}
	}
	return vs
}