Question

I’m playing around with the Android API with a long term prospect of developing a 2D game. Normally, I could live with just using the Canvas for drawing sprites as the graphics for my game. I’d like to be able to perform lots of drawing for visual effects, but it seems that the Android versions prior to Honeycomb (3.0, API level 11) don’t support hardware acceleration.

I’m not sure what that exactly means though. I can’t get myself round to believe that the drawing is done by the CPU, pixel by pixel !?! If I end up having effects like glow, lens effects etc… I’ll be drawing over each pixel quite a few times. Am I right to believe that a typical smartphone CPU will not be able to cope with that at ~30 FPS?

I don’t have the luxury to target Android versions >=3.0 as they constitute 8% of the already not SO big Android market. Should I take my time to go the OpenGL way (I’m a beginner at OpenGL)? If I do so, do you think I’ll gain anything by overlaying a GLSurfaceView taking care of the effects on top of a custom android view using a Canvas to do the drawing otherwise. Or is it for any reason a bad idea to mix the two?

Answer 1

Oh God yes. Esepecially if you’re targetting pre Android 3 devices, going from SurfaceView (with Canvas.drawXxx() calls) to OpenGlSurface works great. Not only do you have faster frames (updates) per second but memory consumption is A LOT better.

Here’s some of the points I’ve noticed:

• If you want to do (multi) sprite animations, doing them with the images loaded as OpenGL textures and displayed on an OpenGL quad gives you a lot more memory space. This is because while regular Bitmap objects are capped by the Android-per-process memory limit (which is something like 16-48 Mb, depending on device and Android version), creating OpenGL textures out of those images (and clearing the iamges right after) doesn’t have this limitation. You’re only limited by the total memory on the device which is A LOT more then 16-48 megs.

Secondly, but still related to this, with Android 2 and below tracking how much memory a Bitmap instance takes is a lot trickier since those intances are not reported against the Java heap memory. They are allocated in some other memory space. In short, another hassle less if you use OpenGL.

• Simple animations such as rotating an image become a breeze with OpenGL. You just texture a quad, then roate it any way you want. Equivalent with Sprite animation is to sequentially display different (rotated versions ) of the image. This is better for memory consumption and speed.

• If you’re doing a 2D-like game, using OpenGL’s orthogonal projection not only simplifies a lot of the (useless, in this case) hassle you’d have with a regular OpenGL perspective projection, but it actually alleviates A LOT of the issues you’d get with regular SurfaceView when needing to scale all your graphical elements so they’d look the same size on different screen resolutions/proportions. With OpenGL’s ortho projection you effectifelly create a fixed area of desired widht and height and then have OpenGL project it on the device screen area automatically.

• It comes without saying that making simple effects such as a pulsating light affecting some graphic element is a lot easier to do with OpenGL (where you just make the light and have it pulsate, and everything is lit accordingly) rather than simulate this with SurfaceView and baked in sprites.

I’ve actually started a small asteriod defence-like game with SurfaceView and Canvas and then quickly switched to OpenGL for the above mentioned reasons. Long story short, the game now looks better, and while it initially ran at 16 UPS on a Samsung TEOS and 30 UPS on an Optimus LG 2x it now runs at 33 UPS on the Teos and about 80 UPS on the LG 2x.