backendbase

type Backend interface {
	Size() (int, int)

	LoadImage(img image.Image) (Image, error)
	LoadImagePattern(data ImagePatternData) ImagePattern
	LoadLinearGradient(data Gradient) LinearGradient
	LoadRadialGradient(data Gradient) RadialGradient

	Clear(pts [4][2]float64)
	Fill(style *FillStyle, pts [][2]float64)
	DrawImage(dimg Image, sx, sy, sw, sh float64, pts [4][2]float64, alpha float64)
	FillImageMask(style *FillStyle, mask *image.Alpha, pts [][2]float64) // pts must have four points

	ClearClip()
	Clip(pts [][2]float64)

	GetImageData(x, y, w, h int) *image.RGBA
	PutImageData(img *image.RGBA, x, y int)

	CanUseAsImage(b Backend) bool
	AsImage() Image // can return nil if not supported
}

type FillStyle struct {
	Color          color.RGBA
	Blur           float64
	LinearGradient LinearGradient
	RadialGradient RadialGradient
	Gradient       struct {
		X0, Y0  float64
		X1, Y1  float64
		RadFrom float64
		RadTo   float64
	}
	ImagePattern ImagePattern
}

type Gradient []GradientStop

type GradientStop struct {
	Pos   float64
	Color color.RGBA
}

type Image interface {
	Width() int
	Height() int
	Size() (w, h int)
	Delete()
	Replace(src image.Image) error
}

type ImagePattern interface {
	Delete()
	Replace(data ImagePatternData)
}

type ImagePatternData struct {
	Image Image
}

type LinearGradient interface {
	Delete()
	Replace(data Gradient)
}

type RadialGradient interface {
	Delete()
	Replace(data Gradient)
}