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 *Transform

	// Dirty is true if we anyhow changed matrix.
	dirty, parentDirty bool

	matrix, parentMatrix, parentInverted Matrix
}

// For implementing the Transformer on embedding.
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
}

// Set the absolute object position.
func (t *Transform) SetPosition(position Vector) {
	t.dirty = true
	t.parentDirty = true
	if t.parent == nil {
		t.position = position
		return
	}

	_, mi := t.parent.MatrixForParenting()
	t.position = position.Apply(mi)
}

// Set the absolute object rotation.
func (t *Transform) SetRotation(rotation Float) {
	t.dirty = true
	t.parentDirty = true
	if t.parent == nil {
		t.rotation = rotation
		return
	}
	t.rotation -= t.parent.Rotation()
}

// Set the absolute object scale.
func (t *Transform) SetScale(scale Vector) {
	t.dirty = true
	t.parentDirty = true
	t.scale = scale
}

func (t *Transform) AddScale(add ...Vector) {
	t.dirty = true
	//t.parentDirty = true
	t.scale = t.scale.Add(add...)
}

func (t *Transform) SetAround(around Vector) {
	t.dirty = true
	t.around = around
}

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

	ret := Transform{}
	ret.position = t.Position()
	ret.rotation = t.Rotation()
	ret.scale = t.Scale()
	ret.around = t.Around()
	ret.dirty = true
	ret.parentDirty = true

	return ret
}

func (t *Transform) Rel() Transform {
	ret := *t
	ret.parent = nil
	return ret
}

// Get the absolute object position.
func (t *Transform) Position() Vector {
	if t.parent == nil {
		return t.position
	}
	pm, _ := t.parent.MatrixForParenting()
	return t.position.Apply(pm)
}

func (t *Transform) Move(v ...Vector) {
	t.SetPosition(t.Position().Add(v...))
}

// Get the absolute object scale.
func (t *Transform) Scale() Vector {
	return t.scale
}

// Get the absolute object rotation.
func (t *Transform) Rotation() Float {
	if t.parent == nil {
		return t.rotation
	}
	return t.rotation + t.parent.Rotation()
}

func (t *Transform) Rotate(add Float) {
	t.dirty = true
	t.rotation += add
}
func (t *Transform) Around() Vector {
	return t.around
}

// Returns true if the object is connected
// to some parent.
func (t *Transform) Connected() bool {
	return t.parent != nil
}

// Connect the object to another one making
// it its parent.
func (t *Transform) Connect(parent Transformer) {
	if parent == nil {
		return
	}
	if t.parent != nil {
		t.Disconnect()
	}

	position := t.Position()
	rotation := t.Rotation()

	t.parent = parent.GetTransform()
	t.SetPosition(position)
	t.SetRotation(rotation)
}

// Disconnect from the parent.
func (t *Transform) Disconnect() {
	if t.parent == nil {
		return
	}
	*t = t.Abs()
}

// Return the matrix and the inverted one for parenting children.
func (t *Transform) MatrixForParenting() (Matrix, Matrix) {
	var m, mi Matrix
	if t.parentDirty {

		//m.Scale(t.scale.X, t.scale.Y)
		m.Rotate(t.rotation)
		m.Translate(t.position.X, t.position.Y)
		t.parentMatrix = m

		mi = m
		mi.Invert()
		t.parentInverted = mi

		t.parentDirty = false
	} else {
		m = t.parentMatrix
		mi = t.parentInverted
	}

	if t.parent != nil {
		pm, pmi := t.parent.MatrixForParenting()
		m.Concat(pm)
		mi.Concat(pmi)
	}

	return m, mi


}

// Returns the GeoM with corresponding
// to the transfrom transformation.
func (t *Transform)Matrix() Matrix {
	var m, pm Matrix

	// Calculating only if we changed the structure anyhow.
	if t.dirty {
		// Scale first.
		m.Scale(t.scale.X, t.scale.Y)
		// Then move and rotate.
		m.Translate(
			-t.around.X * t.scale.X,
			-t.around.Y * t.scale.Y,
		)
		m.Rotate(t.rotation)
		// And finally move to the absolute position.
		m.Translate(t.position.X, t.position.Y)
		t.matrix = m

		// Setting the flag so we d
		t.dirty = false
	} else {
		m = t.matrix
	}

	if t.parent != nil {
		pm, _ = t.parent.MatrixForParenting()
		m.Concat(pm)
	}

	return m
}