Drawing over the same bitmap many times

Issue

I need to produce the effect of drawing a bitmap in a circle shape, this circle will be growing from the center until it reaches the maximum radius, to do that I wrote the following method:

public Bitmap applyDrawingEffect(Bitmap src, int nRadiusprct) 
{
     // image size
    int width = src.getWidth();
    int height = src.getHeight();
    // create bitmap output
    Bitmap result = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
    // set canvas for painting
    Canvas canvas = new Canvas(result);
    canvas.drawARGB(0, 0, 0, 0);

    // config paint
    final Paint paint = new Paint();
    paint.setAntiAlias(true);
    paint.setColor(Color.BLACK);

    // config rectangle for embedding
    final Rect rect = new Rect(0, 0, width, height);
    final RectF rectF = new RectF(rect);

    // draw rect to canvas
    //canvas.drawRoundRect(rectF, round, round, paint);
    float fRadius = (width<=height) ? (width/2) : (height/2);  
    canvas.drawCircle(width/2, height/2, (fRadius * nRadiusprct/100), paint);

    // create Xfer mode
    paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
    // draw source image to canvas
    canvas.drawBitmap(src, rect, rect, paint);

    // return final image
    return result;
}

As you see I passed the radius percentage as a parameter, my question is How I can optimize the code more and more, why do I need to create a bitmap everytime and assign it to a new canvas instance and repaint again....

Is there any way to create a single bitmap and draw over it many times to produce the same effect.

Solution

For the simple way to use a canvas and a bitmap, you can use it along with one of Androids animation methods to do the heavy lifting. Below I wrote a translate animation using the value animator to move my bitmap inside of the canvas. It doesn't require recreate the bitmap over and over again.

public void doCanvas(){
    //Create our resources
    Bitmap bitmap = Bitmap.createBitmap(mLittleChef.getWidth(), mLittleChef.getHeight(), Bitmap.Config.ARGB_8888);
    final Canvas canvas = new Canvas(bitmap);
    final Bitmap chefBitmap = BitmapFactory.decodeResource(getResources(),R.drawable.dish_special);
    final Bitmap starBitmap= BitmapFactory.decodeResource(getResources(),R.drawable.star);

    //Link the canvas to our ImageView
    mLittleChef.setImageBitmap(bitmap);

    ValueAnimator animation= ValueAnimator.ofInt(canvas.getWidth(),0,canvas.getWidth());
    animation.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
        @Override
        public void onAnimationUpdate(ValueAnimator animation) {
            int value = (Integer) animation.getAnimatedValue();
            //Clear the canvas
            canvas.drawColor(Color.TRANSPARENT, PorterDuff.Mode.CLEAR);
            canvas.drawBitmap(chefBitmap, 0, 0, null);
            canvas.save();
            canvas.translate(value,0);
            canvas.drawBitmap(starBitmap, 0, 0, null);
            canvas.restore();
            //Need to manually call invalidate to redraw the view
            mLittleChef.invalidate();
        }
    });
    animation.addListener(new AnimatorListenerAdapter(){
        @Override
        public void onAnimationEnd(Animator animation) {
            simpleLock= false;
        }
    });
    animation.setInterpolator(new LinearInterpolator());
    animation.setDuration(mShortAnimationDuration);
    animation.start();
}

For more about the code and canvas, and the different way to use canvas and bitmap see here

Answered By - Whitney