The MIDP API specification states that the call
to paint() occurs asynchronously of the call
to repaint(). The repaint() method will not block waiting for paint() to
finish. The paint() method will either be called
after the caller of repaint() returns to the
implementation (if the caller is a callback) or on another thread
entirely.
MIDlets cannot assume that paint() is always called immediately after repaint() call. Several repaint() calls can be combined
into one paint() call.
If possible, use GameCanvas, since it has
better control on game painting . There is no performance difference
in Canvas and GameCanvas.
In normal Canvas, to cause paint() call, use serviceRepaints() right after repaint() call.
The MIDP API specification states
that to synchronize with its paint() routine,
applications can use either Display.callSerially() or serviceRepaints(), or explicit synchronization
can be coded into their paint() routine. Games
use a lot of CPU time if the paint() loop is
tight, causing the method to loop and waste CPU time. A game loop
that continuously calls repaint() without any
synchronizing with paint() causes performance
issues. The thread gets as much execution time as, for example the
UI thread.
Avoid using callSerially() and serviceRepaints() together.
Use wait() and notify() instead of Thread.sleep().
Avoid using Timers and TimerTasks, they are heavy operations.
It is possible to design an application so that
it releases its resources when the application goes to the background,
and activates them when the application is in foreground. For Canvas applications, use hideNotify() and showNotify(). For other Displayables, pauseApp() and startApp() are used. You can do this with the JAD attribute Nokia-MIDlet-Background-Event. Normally events
that go to the background causing a call to pauseApp() method do not occur during MIDlet runtime. Use the attribute to
enable multiple pauseApp() / startApp() calls during MIDlet runtime session.
The application needs
to handle the release of its resources itself when pauseApp() is called, call to pauseApp() does not pause
any operations automatically. Normally if Canvas is the current Displayable, it gets hideNotify().
Stop all activities (stop the game loop) and release resources when application goes to the background. Use a tool for memory management, EnergyProfiler, to observe that MIDlet is not consuming resources in the background.
MMAPI: audio/video playing can be stopped (AOB to check: if attribute is not used, MMAPI playing continues normally in background, audio and video plays normally but it is not displayed, sound can be heard)
Networking: network connections can be closed by MIDlet (use
of Timer).
Location API: applications can set LocationListener to null to shut down the GPS.
UI operations: GameCanvas allows drawing on the background. If GameCanvas is used, it is recommended not to draw anything.
If an application is multi-threaded, it is the application developer's responsibility to ensure that threads are synchronized properly to get desired behavior, that is, the calls are sequenced as needed. It the application does not follow basic thread synchronization, the behavior is not guaranteed.
Accessing
a given MMAPI object (DataSource , Player and Controls) from different
threads, behavior depends on the thread scheduling. For consistent
behavior (when accessing a given MMAPI object simultaneously from
different threads) it is recommended to use Java synchronization mechanism
to synchronize access to MMAPI object. When working on games that
use MMAPI video playback:
Resizing video content before playing it if video has been produced in other than mobile device, usable for non-hardware accelerated products
Recommended bit rates depend on resolution.
Accessing MMAPI objects (DataSource , Player, Controls) simultaneously
from more than one thread
Game Design (Design and User Experience Library)
Writing MIDP 2.0 Games (Symbian Developer Community)
Java ME Games and Graphics Training Course (Nokia Developer)
Nokia Energy Profiler (Nokia Developer)
Java Memory Management (Nokia Developer)