go interface func

原文链接： go interface func

// Model can convert any Color to one from its own color model. The conversion
// may be lossy.
type Model interface {
	Convert(c Color) Color
}

// ModelFunc returns a Model that invokes f to implement the conversion.
func ModelFunc(f func(Color) Color) Model {
	// Note: using *modelFunc as the implementation
	// means that callers can still use comparisons
	// like m == RGBAModel. This is not possible if
	// we use the func value directly, because funcs
	// are no longer comparable.
	return &modelFunc{f}
}

type modelFunc struct {
	f func(Color) Color
}

func (m *modelFunc) Convert(c Color) Color {
	return m.f(c)
}

// Models for the standard color types.
var (
	RGBAModel    Model = ModelFunc(rgbaModel)
	RGBA64Model  Model = ModelFunc(rgba64Model)
	NRGBAModel   Model = ModelFunc(nrgbaModel)
	NRGBA64Model Model = ModelFunc(nrgba64Model)
	AlphaModel   Model = ModelFunc(alphaModel)
	Alpha16Model Model = ModelFunc(alpha16Model)
	GrayModel    Model = ModelFunc(grayModel)
	Gray16Model  Model = ModelFunc(gray16Model)
)

func rgbaModel(c Color) Color {
	if _, ok := c.(RGBA); ok {
		return c
	}
	r, g, b, a := c.RGBA()
	return RGBA{uint8(r >> 8), uint8(g >> 8), uint8(b >> 8), uint8(a >> 8)}
}

func rgba64Model(c Color) Color {
	if _, ok := c.(RGBA64); ok {
		return c
	}
	r, g, b, a := c.RGBA()
	return RGBA64{uint16(r), uint16(g), uint16(b), uint16(a)}
}

func (p *RGBA) Set(x, y int, c color.Color) {
	if !(Point{x, y}.In(p.Rect)) {
		return
	}
	i := p.PixOffset(x, y)
	c1 := color.RGBAModel.Convert(c).(color.RGBA)
	s := p.Pix[i : i+4 : i+4] // Small cap improves performance, see https://golang.org/issue/27857
	s[0] = c1.R
	s[1] = c1.G
	s[2] = c1.B
	s[3] = c1.A
}

type Color interface {
	// RGBA returns the alpha-premultiplied red, green, blue and alpha values
	// for the color. Each value ranges within [0, 0xffff], but is represented
	// by a uint32 so that multiplying by a blend factor up to 0xffff will not
	// overflow.
	//
	// An alpha-premultiplied color component c has been scaled by alpha (a),
	// so has valid values 0 <= c <= a.
	RGBA() (r, g, b, a uint32)
}

color.RGBAModel.Convert(c).(color.RGBA)

首先 RGBAModel 是color 包中一个·接口对象·
RGBAModel Model

Model 是 color 包中的一个接口 具备 Convert(c Color) Color 方法 转换之后返回 Color 对象。