# package draw
`import "image/draw"`
draw包提供了圖像合成函數。參見:[http://golang.org/doc/articles/image_draw.html](http://golang.org/doc/articles/image_draw.html)
## Index
* [type Quantizer](#Quantizer)
* [type Image](#Image)
* [type Drawer](#Drawer)
* [type Op](#Op)
* [func (op Op) Draw(dst Image, r image.Rectangle, src image.Image, sp image.Point)](#Op.Draw)
* [func Draw(dst Image, r image.Rectangle, src image.Image, sp image.Point, op Op)](#Draw)
* [func DrawMask(dst Image, r image.Rectangle, src image.Image, sp image.Point, mask image.Image, mp image.Point, op Op)](#DrawMask)
## type [Quantizer](https://github.com/golang/go/blob/master/src/image/draw/draw.go#L26 "View Source")
```
type Quantizer interface {
// Quantize方法向p中最多增加cap(p)-len(p)個色彩并返回修正后的調色板
// 返回值更適合(可以更少失真的)將m轉換為一個調色板類型的圖像
Quantize(p color.Palette, m image.Image) color.Palette
}
```
Quantizer接口為一個圖像生成調色板。
## type [Image](https://github.com/golang/go/blob/master/src/image/draw/draw.go#L20 "View Source")
```
type Image interface {
image.Image
Set(x, y int, c color.Color)
}
```
Image接口比image.Image接口多了Set方法,該方法用于修改單個像素的色彩。
## type [Drawer](https://github.com/golang/go/blob/master/src/image/draw/draw.go#L49 "View Source")
```
type Drawer interface {
// 對齊圖像dst的r.Min和src的sp點,然后將src繪制到dst上的結果來替換矩形范圍內的圖像
Draw(dst Image, r image.Rectangle, src image.Image, sp image.Point)
}
```
Drawer包含Draw方法。
```
var FloydSteinberg Drawer = floydSteinberg{}
```
FloydSteinberg是采用Src操作并實現了Floyd-Steinberg誤差擴散算法的Drawer。
## type [Op](https://github.com/golang/go/blob/master/src/image/draw/draw.go#L33 "View Source")
```
type Op int
```
Op是Porter-Duff合成的操作符。
```
const (
// 源圖像透過遮罩后,覆蓋在目標圖像上(類似圖層)
Over Op = iota
// 源圖像透過遮罩后,替換掉目標圖像
Src
)
```
### func (Op) [Draw](https://github.com/golang/go/blob/master/src/image/draw/draw.go#L44 "View Source")
```
func (op Op) Draw(dst Image, r image.Rectangle, src image.Image, sp image.Point)
```
Draw方法通過使用Op參數調用包的Draw函數實現了Drawer接口。
## func [Draw](https://github.com/golang/go/blob/master/src/image/draw/draw.go#L97 "View Source")
```
func Draw(dst Image, r image.Rectangle, src image.Image, sp image.Point, op Op)
```
Draw函數使用nil的mask參數調用DrawMask函數。
## func [DrawMask](https://github.com/golang/go/blob/master/src/image/draw/draw.go#L103 "View Source")
```
func DrawMask(dst Image, r image.Rectangle, src image.Image, sp image.Point, mask image.Image, mp image.Point, op Op)
```
對齊目標圖像dst的矩形r左上角、源圖像src的sp點、遮罩mask的mp點,根據op修改dst的r矩形區域內的內容,mask如果為nil則視為完全透明。
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