gg/camera.go

package gg

// Implements the camera component
// for the main window.
type Camera struct {
	// The shaders that will be applied to everything
	// that the camera shows.
	ShaderOptions
	Transform
	buffered bool
	buf Matrix
	engine *Engine
}

func (e *Engine) NewCamera() *Camera {
	ret := &Camera{}
	ret.Transform = T()
	ret.engine = e
	return ret
}

// Returns the matrix satysfying camera
// position, scale and rotation to apply
// it to the objects to get the real
// transform to display on the screen.
func (c *Camera)RealMatrix() Matrix {
	// Bufferization
	if c.buffered {
		return c.buf
	}
	g := Matrix{}
	position := c.Position().Neg()
	around := c.Around()
	scale  := c.Scale()
	rotation := c.Rotation()

	g.Translate(-position.X, -position.Y)
	g.Rotate(rotation)

	size := c.engine.AbsWinSize()
	g.Translate(around.X * size.X, around.Y * size.Y)

	g.Scale(scale.X, scale.Y)

	c.buf = g
	c.buffered = true

	return g
}

// The matrix to convert things into the 
// inside engine representation, 
// get the position of cursor inside the world
// basing on its window position.
func (c *Camera) AbsMatrix() Matrix {
	m := c.RealMatrix()
	m.Invert()
	return m
}