Android Canvas drawBitmap 的一个效率问题

canvas.drawBitmap(wpBitmap,

new Rect(0, 0, wpBitmap.getWidth(), wpBitmap.getHeight()),

new Rect(0, 0, source.getWidth(), source.getHeight()),

paint);

Matrix mMatrix = new Matrix();

mMatrix.postScale((float) source.getWidth() / wpBitmap.getWidth(),

(float) source.getHeight() / wpBitmap.getHeight());

canvas.drawBitmap(wpBitmap, mMatrix, paint);