ch13.htm

JAVA Developing Professional JavaApplets

<BR>
&nbsp;&nbsp;&nbsp;&nbsp;/**<BR>
&nbsp;&nbsp;&nbsp;&nbsp; * Standard paint routine for an applet.
<BR>
&nbsp;&nbsp;&nbsp;&nbsp; * @param g contains the Graphics class
to use for painting<BR>
&nbsp;&nbsp;&nbsp;&nbsp; */<BR>
&nbsp;&nbsp;&nbsp;&nbsp;public void paint(Graphics g)<BR>
&nbsp;&nbsp;&nbsp;&nbsp;{<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if ( complete
)<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;{<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;g.drawImage(allImages[current],
roll_x, 40, this);<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;else<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;{<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;g.drawString(&quot;Images
not yet loaded&quot;, 0, 20);<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;public void start()<BR>
&nbsp;&nbsp;&nbsp;&nbsp;{<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if ( animation
== null )<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;{<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;animation
= new Thread(this);<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;animation.start();
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;public void stop()<BR>
&nbsp;&nbsp;&nbsp;&nbsp;{<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if ( animation
!= null )<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;{<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;animation.stop();
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;animation
= null;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;public void run()<BR>
&nbsp;&nbsp;&nbsp;&nbsp;{<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;while ( !checkRoll()
) sleep(250);<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;complete = true;
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;while (true)<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;{<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;roll(0,
this.size().width-42);&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// roll
left to right<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;roll(this.size().width-42,
0);&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// roll right to left<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;boolean checkRoll()<BR>
&nbsp;&nbsp;&nbsp;&nbsp;{<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;boolean finished
= true;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;for ( int i =
0; i &lt; 4; i++ )<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;{<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if
( (tracker.statusID(i, true) &amp; MediaTracker.COMPLETE) == 0
)<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;finished
= false;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;return finished;
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;void roll(int begin, int end)<BR>
&nbsp;&nbsp;&nbsp;&nbsp;{<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if ( begin &lt;
end )<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;{<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;for
( int x = begin; x &lt;= end; x += 21 )<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;{
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;roll_x
= x;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;repaint();
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;current--;
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if
( current == -1 ) current = 3;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;sleep(150);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;else<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;{<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;for
( int x = begin; x &gt;= end; x -= 21 )<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;{
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;roll_x
= x;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;repaint();
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;current++;
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if
( current == 4 ) current = 0;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;sleep(150);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;/**<BR>
&nbsp;&nbsp;&nbsp;&nbsp; * A simple sleep routine<BR>
&nbsp;&nbsp;&nbsp;&nbsp; * @param a the number of milliseconds
to sleep<BR>
&nbsp;&nbsp;&nbsp;&nbsp; */<BR>
&nbsp;&nbsp;&nbsp;&nbsp;private void sleep(int a)<BR>
&nbsp;&nbsp;&nbsp;&nbsp;{<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;try<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;{<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Thread.currentThread().sleep(a);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;catch (InterruptedException
e)<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;{<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
}</TT>
</BLOCKQUOTE>
<HR>
<P>
The first thing the <TT>run()</TT>
method does is start loading the four images; this is done by
using a MediaTracker object. It would have been more efficient
to assign the same ID to all four, but I wanted to show you how
to track individual images as well. When all the images have loaded,
the animation can start. The <TT>run()</TT>
thread updates the <TT>roll_x</TT>
variable and image number every 150 milliseconds, and then issues
a repaint request.
<P>
The <TT>paint()</TT> method simply
draws the current image to the requested location.<BR>
<P><CENTER><TABLE BORDERCOLOR=#000000 BORDER=1 WIDTH=80%>
<TR VALIGN=TOP><TD><B>Note</B></TD></TR>
<TR VALIGN=TOP><TD>
<BLOCKQUOTE>
This applet will work even if the images are not preloaded with MediaTracker; however, failing to preload causes incomplete images to display. The object's position updates even though there are no images to paint. It's much more professional to wait until all the images are complete before beginning an animation.</BLOCKQUOTE>

</TD></TR>
</TABLE></CENTER>
<P>
<P>
To really appreciate the power behind Java images, you need to
understand the consumer/<BR>
producer model in detail. Powerful graphics applications use the
advantages of this model to perform their visual wizardry. In
particular, you can write effective image filters only if you
understand the underlying model.
<H2><A NAME="ImageProducers"><FONT SIZE=5 COLOR=#FF0000>Image
Producers</FONT></A></H2>
<P>
The ImageProducer interface has the following methods:
<UL>
<LI><TT>public void addConsumer(ImageConsumer
ic);</TT>
<LI><TT>public boolean isConsumer(ImageConsumer
ic);</TT>
<LI><TT>public void removeConsumer(ImageConsumer
ic);</TT>
<LI><TT>public void startProduction(ImageConsumer
ic);</TT>
<LI><TT>public void requestTopDownLeftRightResend(ImageConsumer
ic);</TT>
</UL>
<P>
Notice that all the methods require an ImageConsumer object. There
are no backdoors; an ImageProducer can output only through an
associated ImageConsumer. A given producer can have multiple objects
as client consumers, though this is not usually the case. Typically,
as soon as a consumer registers itself with a producer <TT>[addConsumer()]</TT>,
the image data is immediately delivered through the consumer's
interface.
<H3><A NAME="ImageConsumers">Image Consumers</A></H3>
<P>
The ImageProducer interface is clean and straightforward, but
the ImageConsumer is quite a bit more complex. It has the following
methods:
<UL>
<LI><TT>public void setDimensions(int width,
int height);</TT>
<LI><TT>public void setProperties(Hashtable
props);</TT>
<LI><TT>public void setColorModel(ColorModel
model);</TT>
<LI><TT>public void setHints(int hintflags);</TT>
<LI><TT>public void setPixels(int x, int
y, int w, int h, ColorModel model, byte pixels[], int off, int
scansize);</TT>
<LI><TT>public void setPixels(int x, int
y, int w, int h, ColorModel model, int pixels[], int off, int
scansize);</TT>
<LI><TT>public void imageComplete(int status);</TT>
</UL>
<P>
Figure 13.1 shows the normal progression of calls to the ImageConsumer
interface. Several methods are optional: <TT>setProperties()</TT>,
<TT>setHints()</TT>, and <TT>setColorModel()</TT>.
The core methods are first <TT>setDimensions()</TT>,
followed by one or more calls to <TT>setPixels()</TT>.
Finally, when there are no more <TT>setPixels()</TT>
calls, <TT>imageComplete()</TT> is
invoked.
<P>
<A HREF="f13-1.gif" ><B>Figure 13.1 : </B><I>Normal flow of calls to an ImageConsumar.</I></A>
<P>
Each image has fixed rectangular dimensions, which are passed
in <TT>setDimensions()</TT>. The consumer
needs to save this data for future reference. The <TT>setProperties()</TT>
method has no discernible use right now, and most consumers don't
do anything with it. The hint flags, however, are a different
story. <I>Hints</I> are supposed to give clues about the format
of the producer's data. Table 13.1 lists the values for hint flags.
<BR>
<P>
<CENTER><B>Table 13.1. Hint flag values for </B><TT><B>setHints()</FONT></B></TT><B><FONT SIZE=5>.</FONT></B></CENTER>
<P><CENTER><TABLE BORDERCOLOR=#000000 BORDER=1 WIDTH=80%>
<TR VALIGN=TOP><TD WIDTH=152><I>Name</I></TD><TD WIDTH=438><I>Meaning</I>
</TD></TR>
<TR VALIGN=TOP><TD WIDTH=152><TT>RANDOMPIXELORDER=1</TT>
</TD><TD WIDTH=438>No assumptions should be made about the delivery of pixels.
</TD></TR>
<TR VALIGN=TOP><TD WIDTH=152><TT>TOPDOWNLEFTRIGHT=2</TT>
</TD><TD WIDTH=438>Pixel delivery will paint in top to bottom, left to right.
</TD></TR>
<TR VALIGN=TOP><TD WIDTH=152><TT>COMPLETESCANLINES=4</TT>
</TD><TD WIDTH=438>Pixels will be delivered in multiples of complete rows.
</TD></TR>
<TR VALIGN=TOP><TD WIDTH=152><TT>SINGLEPASS=8</TT>
</TD><TD WIDTH=438>Pixels will be delivered in a single pass. No pixel will appear in more than one <TT>setPixel()</TT> call.
</TD></TR>
<TR VALIGN=TOP><TD WIDTH=152><TT>SINGLEFRAME=16</TT>
</TD><TD WIDTH=438>The image consists of a single static frame.
</TD></TR>
</TABLE></CENTER>
<P>
<P>
When all the pixel information has been transmitted, the producer
will call <TT>imageComplete()</TT>.
The status parameter will have one of three values: <TT>IMAGEERROR=1</TT>,
<TT>SINGLEFRAMEDONE=2</TT>, or <TT>STATICFRAMEDONE=3</TT>.
<P>
<TT>SINGLEFRAMEDONE</TT> indicates
that additional frames will follow; for example, a video camera
would use this technique. Special-effect filters could also use
<TT>SINGLEFRAMEDONE</TT>. <TT>STATICFRAMEDONE</TT>
is used to indicate that no more pixels will be transmitted for
the image. The consumer should remove itself from the producer
after receiving <TT>STATICFRAMEDONE</TT>.
<P>
The two <TT>setPixels()</TT> calls
provide the image data. Keep in mind that the image size was set
by <TT>setDimensions()</TT>. The array
within <TT>setPixels()</TT> calls
does not necessarily contain all the pixels within an image. In
fact, it usually contains only a rectangular subset of the total
image. Figure 13.2 shows a rectangle of <TT>setPixels()</TT>
within an entire image.
<P>
<A HREF="f13-2.gif" ><B>Figure 13.2 : </B><I>The relationship of </I>SetPixels()<I> calls to an entire image.</I></A>
<P>
The row size of the array is the <TT>scansize</TT>.
The width and height parameters indicate the usable pixels within
the array, and the offset contains the starting index. It is up
to the consumer to map the passed array onto the entire image.
The sub-image's location within the total image is contained in
the <TT>x</TT> and <TT>y</TT>
parameters.
<P>
The ColorModel contains all needed color information for the image.
The call to <TT>setColorModel()</TT>
is purely informational because each <TT>setPixels()</TT>
call passes a specific ColorModel parameter. No assumptions should
be made about the ColorModel from <TT>setColorModel()</TT>
calls.
<H2><A NAME="FilteringanImage"><FONT SIZE=5 COLOR=#FF0000>Filtering
an Image</FONT></A></H2>
<P>
Image filters sit between an ImageProducer and an ImageConsumer
and must implement both these interfaces. Java supplies two separate