package graphics

type Rect struct {
	X      int
	Y      int
	Width  int
	Height int
}

type TexturePart struct {
	LocationX int
	LocationY int
	Source    Rect
}

type Filter int

const (
	FilterNearest Filter = iota
	FilterLinear
)

type TextureQuad struct {
	VertexX1       float32
	VertexX2       float32
	VertexY1       float32
	VertexY2       float32
	TextureCoordU1 float32
	TextureCoordU2 float32
	TextureCoordV1 float32
	TextureCoordV2 float32
}

type TextureId int

// A render target is essentially same as a texture, but it is assumed that the
// all alpha of a render target is maximum.
type RenderTargetId int

func OrthoProjectionMatrix(left, right, bottom, top int) [4][4]float64 {
	e11 := float64(2) / float64(right-left)
	e22 := float64(2) / float64(top-bottom)
	e14 := -1 * float64(right+left) / float64(right-left)
	e24 := -1 * float64(top+bottom) / float64(top-bottom)

	return [4][4]float64{
		{e11, 0, 0, e14},
		{0, e22, 0, e24},
		{0, 0, 1, 0},
		{0, 0, 0, 1},
	}
}