var (
	// NearestNeighbor is the nearest neighbor interpolator. It is very fast,
	// but usually gives very low quality results. When scaling up, the result
	// will look 'blocky'.
	NearestNeighbor = Interpolator(nnInterpolator{})

	// ApproxBiLinear is a mixture of the nearest neighbor and bi-linear
	// interpolators. It is fast, but usually gives medium quality results.
	//
	// It implements bi-linear interpolation when upscaling and a bi-linear
	// blend of the 4 nearest neighbor pixels when downscaling. This yields
	// nicer quality than nearest neighbor interpolation when upscaling, but
	// the time taken is independent of the number of source pixels, unlike the
	// bi-linear interpolator. When downscaling a large image, the performance
	// difference can be significant.
	ApproxBiLinear = Interpolator(ablInterpolator{})

	// BiLinear is the tent kernel. It is slow, but usually gives high quality
	// results.
	BiLinear = &Kernel{1, func(t float64) float64 {
		return 1 - t
	}}

	// CatmullRom is the Catmull-Rom kernel. It is very slow, but usually gives
	// very high quality results.
	//
	// It is an instance of the more general cubic BC-spline kernel with parameters
	// B=0 and C=0.5. See Mitchell and Netravali, "Reconstruction Filters in
	// Computer Graphics", Computer Graphics, Vol. 22, No. 4, pp. 221-228.
	CatmullRom = &Kernel{2, func(t float64) float64 {
		if t < 1 {
			return float64((float64(1.5*t)-2.5)*t*t) + 1
		}
		return float64((float64(float64(float64(-0.5*t)+2.5)*t)-4)*t) + 2
	}}
)

type Drawer = draw.Drawer

var FloydSteinberg Drawer = floydSteinberg{}

type Image = draw.Image

type Interpolator interface {
	Scaler
	Transformer
}

type Kernel struct {
	// Support is the kernel support and must be >= 0. At(t) is assumed to be
	// zero when t >= Support.
	Support float64
	// At is the kernel function. It will only be called with t in the
	// range [0, Support).
	At func(t float64) float64
}

type Op = draw.Op

const (
	// Over specifies ``(src in mask) over dst''.
	Over Op = draw.Over
	// Src specifies ``src in mask''.
	Src Op = draw.Src
)

type Options struct {
	// Masks limit what parts of the dst image are drawn to and what parts of
	// the src image are drawn from.
	//
	// A dst or src mask image having a zero alpha (transparent) pixel value in
	// the respective coordinate space means that dst pixel is entirely
	// unaffected or that src pixel is considered transparent black. A full
	// alpha (opaque) value means that the dst pixel is maximally affected or
	// the src pixel contributes maximally. The default values, nil, are
	// equivalent to fully opaque, infinitely large mask images.
	//
	// The DstMask is otherwise known as a clip mask, and its pixels map 1:1 to
	// the dst image's pixels. DstMaskP in DstMask space corresponds to
	// image.Point{X:0, Y:0} in dst space. For example, when limiting
	// repainting to a 'dirty rectangle', use that image.Rectangle and a zero
	// image.Point as the DstMask and DstMaskP.
	//
	// The SrcMask's pixels map 1:1 to the src image's pixels. SrcMaskP in
	// SrcMask space corresponds to image.Point{X:0, Y:0} in src space. For
	// example, when drawing font glyphs in a uniform color, use an
	// *image.Uniform as the src, and use the glyph atlas image and the
	// per-glyph offset as SrcMask and SrcMaskP:
	//	Copy(dst, dp, image.NewUniform(color), image.Rect(0, 0, glyphWidth, glyphHeight), &Options{
	//		SrcMask:  glyphAtlas,
	//		SrcMaskP: glyphOffset,
	//	})
	DstMask  image.Image
	DstMaskP image.Point
	SrcMask  image.Image
	SrcMaskP image.Point
}

type Quantizer = draw.Quantizer

type RGBA64Image = draw.RGBA64Image

type Scaler interface {
	Scale(dst Image, dr image.Rectangle, src image.Image, sr image.Rectangle, op Op, opts *Options)
}

type Transformer interface {
	Transform(dst Image, m f64.Aff3, src image.Image, sr image.Rectangle, op Op, opts *Options)
}