Using Images and Timers
The Waba foundation classes contain methods and classes to deal
with images and timers. We'll explain the basics here along with
some sample code that should give you a feel for how they can be used.
Let's start with images. The Image class in the waba.fx package represents
In this example, we load an image called "hello.bmp" and draw it at location
10, 10 in the application window:
public class MyApp extends MainWindow
public void onStart()
img = new Image("hello.bmp");
public void onPaint(Graphics g)
g.drawImage(img, 10, 10);
So, how did we create the hello.bmp image? The hello.bmp image is a
Microsoft BMP format image. BMP is a standard image format for bitmap images.
Waba supports 2, 16 and 256 color uncompressed BMP images.
These image types are supported by most paint programs.
If you could use the Paint program that comes with Windows 95 or NT,
you can save an image out as a "Monochrome Bitmap" BMP image to use
it in a Waba program. In Paint Shop Pro (from JASC, Inc), you could
save out an image as "BMP - OS/2 or Windows Bitmap" and
"Windows RGB Encoded".
If you load BMP images in your program, you should include them in
your program's WARP file.
Here is an example of executing a command to "warp up" all the classes
and images in the current directory into a single WARP file:
> warp c /q Hello *.class *.bmp
Using Images in Java Applets
If you distribute your Waba program as a Java applet, there is something
you should know if your Waba program uses images: the image files should
be included in a JAR file.
Before we explain this in detail, let's review how to put a Waba program on the web so it
can run as a Java applet in a web page.
You can put a Waba program up on the web as a Java applet by placing
all your program's classes and all the Waba foundation classes in
the WabaSDK up on the web under a directory such that the
directory hierarchy looks like this:
The following HTML code would make the applet appear in the
<param name=appClass value="MyApp">
To make the applet load faster, it's common to create a JAR file containing
the applet's classes. A "jar" program is used to create and manage JAR
files. The jar program is part of Java Development Kit distributions like
the JDK from Sun Microsystems.
You can make a JAR file containing the Waba program as you normally
would, but the trick is the JAR file should not contain the images used by
It should only contain the program's classes:
> jar cvf MyApp.jar *.class waba/applet/*.class
waba/fx/*.class waba/io/*.class waba/sys/*.class
The image files should be placed on the web site separate from
the JAR file as follows:
Then the HTML code that references the applet can be changed to load
the applet from a JAR file:
width=160 height=160 archive=MyApp.jar>
<param name=appClass value="MyApp">
The image files can't be in the JAR file because some web browsers
don't expect anything but .class files to exist in a JAR file.
There are times where you don't want to load an image and, instead,
just want to create an image and draw in it yourself. One common use
of off-screen images is as a drawing buffer to perform double-buffered drawing.
In this example, we create a 10x10 image with a black background and draw a white
X in the image:
Image img = new Image(10, 10);
Graphics g = new Graphics(image);
g.setColor(0, 0, 0);
g.fillRect(0, 0, 10, 10);
g.setColor(255, 255, 255);
g.drawLine(0, 0, 9, 9);
g.drawLine(0, 9, 9, 0);
Notice that we filled the image with a black background before drawing lines inside
of it. The contents of an image are initially undefined.
When you want to draw an image to the screen, you don't have to draw the whole image.
You can draw portions of it using the Graphics.copyRect() method. There are
also various copy "modes" available to copy it with logical OR, AND and XOR
The extended drawing modes are not available when running with the Java bridge
classes (those in the WabaSDK). They are only available when running under a native
Now let's take a look at timers. Timers are associated with user-interface
controls. Any user-interface control in a Waba program can have its
Timers are created and destroyed using two methods in the Control class:
Timer Control.addTimer(int millis);
boolean Control.removeTimer(Timer timer);
When a timer ticks, it posts a ControlEvent.TIMER event to the control
associated with the timer.
Here we create a new control by subclassing the Control class.
The control contains methods to start and stop blinking.
The blinking timer fires 5 times a second (every 200 milliseconds).
public class MyControl extends Control
public void startBlinking()
timer = addTimer(200);
public void stopBlinking()
public void onEvent(Event event)
if (event.type == ControlEvent.TIMER)
The timer does not interrupt your program in the middle of an operation. It
is scheduled along with other events. So, if your program is in the middle
of computing something when the timer is supposed to tick, it will tick
as soon as it can.
Another method that is timing related but not directly related to timers is
This method returns a time stamp in milliseconds. It is a running timestamp
which means when the value goes beyond the value 1073741824 (which is
1 << 30), it wraps around to 0. It has no connection to the current
time, it is only useful when calculating relative times.
The current time is available by using the Time class.
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