Android drawBitmap Performance For Lots of Bitmaps?

Question

I'm in the process of writing an Android game and I seem to be having performance issues with drawing to the Canvas. My game has multiple levels, and each has (obviously) a different number of objects in it.

The strange thing is that in one level, which contains 45 images, runs flawlessly (almost 60 fps). However, another level, which contains 81 images, barely runs at all (11 fps); it is pretty much unplayable. Does this seem odd to anybody besides me?

All of the images that I use are .png's and the only difference between the aforementioned levels is the number of images.

What's going on here? Can the Canvas simply not draw this many images each game loop? How would you guys recommend that I improve this performance?

Thanks in advance.

Answer 1

Seems strange to me as well. I am also developing a game, lots of levels, I can easily have a 100 game objects on screen, have not seen a similar problem.

Used properly, drawbitmap should be very fast indeed; it is little more than a copy command. I don't even draw circles natively; I have Bitmaps of pre-rendered circles.

However, the performance of Bitmaps in Android is very sensitive to how you do it. Creating Bitmaps can be very expensive, as Android can by default auto-scale the pngs which is CPU intensive. All this stuff needs to be done exactly once, outside of your rendering loop.

I suspect that you are looking in the wrong place. If you create and use the same sorts of images in the same sorts of ways, then doubling the number of screen images should not reduce performance by a a factor of over 4. At most it should be linear (a factor of 2).

My first suspicion would be that most of your CPU time is spent in collision detection. Unlike drawing bitmaps, this usually goes up as the square of the number of interacting objects, because every object has to be tested for collision against every other object. You doubled the number of game objects but your performance went down to a quarter, ie according to the square of the number of objects. If this is the case, don't despair; there are ways of doing collision detection which do not grow as the square of the number of objects.

In the mean time, I would do basic testing. What happens if you don't actually draw half the objects? Does the game run much faster? If not, its nothing to do with drawing.

Answer 2

I think this lecture will help you. Go to the 45 minute . There is a graph comparing the Canvas method and the OpenGl method. I think it is the answer.