gg/transform.go

package gg

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

type Transformer interface {
	GetTransform() Transform
}

// The structure represents basic transformation
// features: positioning, rotating and scaling.
type Transform struct {
	// Absolute (if no parent) position and
	// the scale.
	Position, Scale Vector
	// The object rotation in radians.
	Rotation Float
	// The not scaled offset vector from upper left corner
	// which the object should be rotated around.
	Around Vector
	// If is not nil then the upper values will be relational to
	// the parent ones.
	Parent Transformer
}

func (t Transform) GetTransform() Transform {
	return t
}

// Returns the default Transform structure.
func T() Transform {
	ret := Transform{
		// Rotate around
		Scale: Vector{1, 1},
		// Rotate around the center.
		Around: V(.5, .5),
	}
	return ret
}

func (t *Transform) SetAbsPosition(absPosition Vector) {
	if t.Parent == nil {
		t.Position = absPosition
		return
	}
	m := t.ParentMatrix()
	m.Invert()
	t.Position = absPosition.Apply(m)
}

// Get the absolute representation of the transform.
func (t Transform) Abs() Transform {
	if t.Parent == nil {
		return t
	}

	ret := T()
	ret.Position = t.AbsPosition()
	ret.Rotation = t.AbsRotation()
	ret.Scale = t.AbsScale()

	return ret
}

func (t Transform) AbsPosition() Vector {
	if t.Parent == nil {
		return t.Position
	}
	return t.Position.Apply(t.ParentMatrix())
}

func (t Transform) AbsScale() Vector {
	if t.Parent == nil {
		return t.Scale
	}
	return V2(1)
}

func (t Transform) AbsRotation() Float {
	if t.Parent == nil {
		return t.Rotation
	}
	return t.Rotation + t.Parent.GetTransform().AbsRotation()
}

func (t *Transform) SetAbsRotation(rot Float) {
	if t.Parent == nil {
		t.Rotation = rot
	}
	t.Rotation -= t.Parent.GetTransform().AbsRotation()
}

func (t *Transform) Connected() bool {
	return t.Parent != nil
}

func (t *Transform) Connect(parent Transformer) {
	absPosition := t.AbsPosition()
	absRotation := t.AbsRotation()
	t.Parent = parent
	t.SetAbsPosition(absPosition)
	t.SetAbsRotation(absRotation)
}

func (t *Transform) Disconnect() {
	if t.Parent == nil {
		return
	}
	*t = t.Abs()
}

func (t Transform) ParentMatrix() Matrix {
	g := Matrix{}
	if t.Parent == nil {
		return g
	}

	p := t.Parent.GetTransform()
	g = p.ParentMatrix()

	g.Scale(p.Scale.X, p.Scale.Y)
	g.Rotate(p.Rotation)
	g.Translate(p.Position.X, p.Position.Y)

	return g
}

// Returns the GeoM with corresponding
// to the transfrom transformation.
func (t Transform)Matrix() Matrix {
	g := Matrix{}

	// Scale first.
	g.Scale(t.Scale.X, t.Scale.Y)

	// Then move and rotate.
	g.Translate(
		-t.Around.X * t.Scale.X,
		-t.Around.Y * t.Scale.Y,
	)
	g.Rotate(t.Rotation)

	// And finally move to the absolute position.
	g.Translate(t.Position.X, t.Position.Y)

	m := t.ParentMatrix()
	g.Concat(m)

	return g
}