Canvas class is the main template for low-level MIDlet graphics.
Being a low-level API, Canvas offers
more options to customize a MIDlet but the MIDlet won't be as portable as
ones created using only high-level APIs. In contrast to the high-level classes
mentioned above, Canvas enables MIDlet programmers to
draw any graphics on the screen. The MIDlet can use any drawing primitives
provided by the LCDUI Graphics interface.
A common example of a MIDlet that uses Canvas is
a mobile game that requires pixel-accurate drawing and access to low-level
keypad events. At least two simultaneous key presses are supported in Canvas
Displayable.
Canvas is a subclass of Displayable,
and applications can attach Commands to it. This is useful
for implementing high-level actions to a MIDlet. The Canvas methods hideNotify() and showNotify() is called to indicate when the Canvas has been obscured
and unobscured, respectively.
The Canvas class has a full screen mode, where
the whole display area is available to the MIDlet. The full screen mode can
be activated/deactivated by the application by calling the setFullScreenMode function.
In MIDP, a virtual machine is able to trigger various events on Canvas,
such as key presses, releases, repeats, and whether Canvas is
still visible or not.
For more information on Canvas, see Canvas
implementation notes.
For an example of using Canvas, see section Example: Creating a simple
test MIDlet.