Question

I have this code that I call on each touch event that render an alpha masked bitmap:

…

        Canvas canvas = new Canvas();
        Bitmap bleed = BitmapFactory.decodeResource(resources, R.drawable.bleed);
        Bitmap photoBG = BitmapFactory.decodeResource(resources, R.drawable.photo_bg);
        Bitmap mask = BitmapFactory.decodeResource(resources, R.drawable.mask);
        Bitmap result = Bitmap.createBitmap(bleed.getWidth(), bleed.getHeight(), Bitmap.Config.ARGB_8888);


        canvas.setBitmap(result);
        Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
        paint.setAntiAlias(true);
        paint.setFilterBitmap(true);
        paint.setDither(true);
        canvas.drawBitmap(photoBG, 0, 0, paint);
        canvas.drawBitmap(selectedImage, matrix, paint);
        paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_IN));

        canvas.drawBitmap(mask, 0, 0, paint);
        paint.setXfermode(null);
        canvas.drawBitmap(bleed, 0, 0, paint);


        myImageView.setImageBitmap(result);
        bleed.recycle();
        mask.recycle();
        img.invalidate();

    }

…
The result image is ok but when I drag the image around, the performance is really slow, I’ve attached an explanatory image and my app screen capture (Note: the background is gray at the app).

Should I stick to this code (drawing on a canvas) or is there a better way achieving my goal?

Answer 1

You are creating 4 bitmaps on every touch, that’s your performance issue. These are very expensive calls (especially the decode*() calls.) Create/load the btimaps only once 🙂