旋转画布后，位图失去质量

Question

I have a lot of draw operations in my custom view(compass). I decided to optimize it by drawing whole compass on a bitmap in onSizeChanged() method, instead of just drawing it directly every time onDraw() triggers.

Here is a part of onDraw() method:

canvas.rotate(-heading, x, y);
canvas.drawBitmap(compassBitmap, 0f, compassBitmapY, compassBitmapPaint);

My problem is what happens after rotation. Bitmap loses its quality. Setting ANTI_ALIAS_FLAG does not help at all. Is there any way to deal with this problem or should i get back to the "heavier" implementation?

Answer 1

it's impossible to rotate image without loosing it's quality, it's limited by resolution.

Each pixel position need to be recalculed, if new destination is not (int, int) pixels needs to be mixed to be closest from the original image.

http://homepages.inf.ed.ac.uk/rbf/HIPR2/rotate.htm