Canvas and Drawables 翻译第二集

Android官方原文地址：http://developer.android.com/guide/topics/graphics/2d-graphics.html

------以下的翻译融入了自己的思考，便于理解，很多地方翻译并不是很恰当，所以配上了英文原文

Draw with a Canvas 用画板（Canvas）绘制

When you're writing an application in which you would like to perform specialized drawing and/or control the animation of graphics, you should do so by drawing through a

Canvas

.
A Canvas works for you as a pretense, or interface, to the actual surface upon which your graphics will be drawn — it holds all of your "draw" calls. Via the Canvas, your drawing is actually performed upon an underlying

Bitmap

In the event that you're drawing within the

onDraw()

callback
method, the Canvas is provided for you and you need only place your drawing calls upon it. You can also acquire a Canvas from

SurfaceHolder.lockCanvas()

,
when dealing with a SurfaceView object. (Both of these scenarios are discussed in the following sections.) However, if you need to create a new Canvas, then you must define the

Bitmap

upon
which drawing will actually be performed. The Bitmap is always required for a Canvas. You can set up a new Canvas like this:

如果你正在onDraw（）回调方法里绘制，画板（Canvas）已经提供给你，而你只需要用它的绘制方法在它上面绘制。当你要用SurfaceVeiw对象处理的时候，你也能从Surface.lockCanvas（）里获得Canvas。以上两种情况在下面已被讨论。不管怎样，如果你需要创建一个新的Canvas，你必须定义一个Bitmap，绘制实际上是执行在Bitmap上的。这个Bitmap对于Canvas是必须的。你能够设置一个新的Canvas，像这样：

Bitmap b = Bitmap.createBitmap(100, 100, Bitmap.Config.ARGB_8888);
Canvas c = new Canvas(b);

Now your Canvas will draw onto the defined Bitmap. After drawing upon it with the Canvas, you can then carry your Bitmap to another Canvas with one of the

Canvas.drawBitmap(Bitmap,...)

methods.
It's recommended that you ultimately draw your final graphics through a Canvas offered to you by

View.onDraw()

or

SurfaceHolder.lockCanvas()

(see
the following sections).

现在你的Canvas将要绘制图形到这个已经定义的Bitmap上。在Bitmap上绘制之后，你能够通过

Canvas.drawBitmap(Bitmap,...)方法其中的一种

把你的Bitmap搬到另一个Canvas里面。推荐你使用通过View.onDraw（）方法或者SurfaceHolder.lockCanvas（）提供给你的Canvas绘制你最终的图形。

The

Canvas

class has its own set
of drawing methods that you can use, like

drawBitmap(...)

,

drawRect(...)

drawText(...)

,

and many more. Other classes that you might use also have

draw()

methods. For example, you'll probably have some

Drawable

draw()