Canvas and Drawables Translation Episode 2

Android official original address: http://developer.android.com/guide/topics/graphics/2d-graphics.html

------The following translation has been incorporated into itself Thinking, easy to understand, the translation in many places is not very appropriate, so the original English text

Draw with a Canvas Draw with a drawing board (Canvas)

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:

If you are drawing in the onDraw() callback method, the artboard (Canvas) is already provided to you, and you only need to use its The draw method draws on it. When you want to deal with the SurfaceVeiw object, you can also get the Canvas from Surface.lockCanvas(). The above two situations are discussed below. Regardless, if you need to create a new Canvas, you must define a Bitmap, and drawing is actually performed on the Bitmap. This Bitmap is necessary for Canvas. You can set up a new Canvas, like this:

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 ).

Now your Canvas will draw graphics to this defined Bitmap. After drawing on the Bitmap, you can move your Bitmap to another Canvas through

Canvas.drawBitmap(Bitmap,...)方法其中的一种

. It is recommended that you use the Canvas provided to you through the View.onDraw() method or SurfaceHolder.lockCanvas() to draw your final graphics.

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()