CODEWITHSUNDEEP
androidandroid-canvas
Karthik
Karthik

Reputation: 5033

How do I clear the contents of a drawn Canvas in Android?

I would like to clear the contents of the canvas after drawing certain things on the screen.

How do I clear the screen fully? Any snippets of code on it will be helpful.

Thanks.

This is my code:

public class Panel extends SurfaceView implements SurfaceHolder.Callback {

private ViewThread mThread;
private ArrayList<Element> mElements = new ArrayList<Element>();


public Panel(Context context, AttributeSet attrs) { 
    super(context, attrs); 
    this.setBackgroundColor(Color.TRANSPARENT);                 
    this.setZOrderOnTop(true); //necessary                
    getHolder().setFormat(PixelFormat.TRANSPARENT); 
    getHolder().addCallback(this); 
    mThread = new ViewThread(this); 

} 


public void doDraw(Canvas canvas) {
     super.onDraw(canvas);

     //canvas.drawColor(Color.TRANSPARENT);
    // canvas.drawColor(Color.argb(0, 255, 255, 255)); 
    //canvas.drawColor(Color.rgb(-1, -1, -1));
    //canvas.drawARGB(0, 255, 255, 255);
    synchronized (mElements) {
        for (Element element : mElements) {
            element.doDraw(canvas);
        }
    }
}

@Override
public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
    // TODO Auto-generated method stub
}

@Override
public void surfaceCreated(SurfaceHolder holder) {
    if (!mThread.isAlive()) {
        mThread = new ViewThread(this);
        mThread.setRunning(true);
        mThread.start();
    }
}

@Override
public void surfaceDestroyed(SurfaceHolder holder) {
    if (mThread.isAlive()) {
        mThread.setRunning(false);
    }
}

@Override
public boolean onTouchEvent(MotionEvent event) {
    synchronized (mElements) {
        mElements.add(new Element(getResources(), (int) event.getX(), (int) event.getY()));
    }
    return super.onTouchEvent(event);
}

}

Upvotes: 4

Views: 6785

Answers (2)

Scarecrow
Scarecrow

Reputation: 4137

this code

canvas.drawARGB(0, 0, 0, 0);

will make canvas background black,

But if you want to clear the drawing totally and make the canvas background transparent then follow this code

Paint paint = new Paint();
paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR)); 

Rect rect=new Rect(0,0,canvas_width,canvas_height);
canvas.drawRect(rect,paint);

Upvotes: 1

kostja
kostja

Reputation: 61538

Try this : 

canvas.drawColor(0); //use 32bit hex like 0xffffffff for white

or

canvas.drawARGB(0, 0, 0, 0); //0-255 for each component

This will clear the canvas with black. You can use any color you like.

Upvotes: 5

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