TweetFollow Us on Twitter

Jun 02 Cover Story

Volume Number: 18 (2002)
Issue Number: 06
Column Tag: Java Programming

by Andrew S. Downs

Dock Tile Imaging

Changing a Java application’s dock tile at runtime

Overview

The Dock Manager API allows a programmer to alter the tile for an application at runtime. Using the Java Native Interface, a Java application can change its tile dynamically as well. This involves a combination of Java and native code.

Two approaches are illustrated in this article. The first captures the pixels from a Java image and passes them to a native library function, which uses the CoreGraphics (Quartz) API to replace the application’s tile (see Figure 1).


Figure 1. A modified Dock tile.

The second example uses QuickDraw to paint a progress bar over the tile, as shown in Figure 2. The progress data is sent from Java to a native library function, and the imaging is done in the library.


Figure 2. The progress bar at the bottom of the tile, showing 60% complete.

If you want to code along with the examples, my recommendation is to first download the JNISample project from Apple’s developer site (see the URLs at the end of this article). That project served as the structural basis for the code in this article. All the build settings are already in place, making it an easy-to-use learning tool. (There are targets for compiling both the Java and native code, generating the javah file, building a library, etc.) I kept the filenames the same, but replaced the content of the various files. In the listings below you will see the filenames as they exist in that project.

Java

One class (DockTiler) provides most of the functionality for this example. It relies on two other classes for getting and drawing (offscreen) an image from a local file. You can also load an image via a non-local URL, which would allow the app to change the tile in response to outside conditions. For example, an application that retrieves weather data can change the tile to reflect current conditions or the forecast.

The JNISample class contains main(), the entry point for the Java application. It is used simply to instantiate DockTiler and invoke one of its instance methods.

Listing 1: JNISample.java

JNISample
The classes contained here include:
   JNISample: creates and calls a DockTiler instance.
   DockTiler: loads the image and sends it to the native drawing code.
   LocalFiler: allows the user to select a local file for display in the tile.
   PictureFrame: an offscreen Canvas which draws the image, allowing DockTiler
    to retrieve the image pixels.

// The image support comes from the AWT and the image package. 
import java.awt.*;
import java.awt.image.*;
import java.util.*;

public class JNISample {
   public JNISample() {}

   // Test code.
   public static void main (String args[]) {
      DockTiler dock = new DockTiler();
        
      dock.test();

      System.out.println( “Finished.” );
   }
}

class DockTiler {
   // If we have trouble loading an image, the values of its width and height will 
   // remain at -1. See loadImage().
   int mWidth = -1, mHeight = -1;
   int mPixels[];

   static {
      // Load the library when this class gets loaded.
      System.loadLibrary( “Example” );
   }

   public DockTiler() {
   }
   
   // These are the two functions in the shared library that we will call.
   // Note the declaration as native.
   native void setDockTile( int[] pixels, int width, 
      int height );

   native void updateProgressBar( int currPercent );
   
   // The primary test driver.
   public void test() {
      loadImage();
      
      setDockTile( mPixels, mWidth, mHeight );

      performTask();
   }

   // Read in the image and retrieve its pixels.
   protected void loadImage() {
      LocalFile lf = new LocalFile();
      String filename = lf.getFilePath();
      
      Image image = 
         Toolkit.getDefaultToolkit().getImage( filename );

      // Send the image to the Canvas, where it will be rendered.
      PictureFrame pf = new PictureFrame( image );
      
      Frame f = new Frame( “Image” );

      // Setup offscreen.
      f.setBounds( -250, -250, 200, 200 );

      f.setLayout( new BorderLayout() );
      f.add( “Center”, pf );
      pf.setSize( 128, 128 );
      f.pack();

      // An invisible window won’t render an image.
      f.setVisible( true );

      f.repaint();
      pf.repaint();
      
      // Use the Canvas as the observer during the loading process.
      int width = image.getWidth( pf );
      int height = image.getHeight( pf );
      
      // Allocate storage for the image data.
      mPixels = new int[ width * height ];
         
      // Create an object to copy the image pixel data into our array.
      PixelGrabber pg = new PixelGrabber( image, 0, 0, 
         width, height, mPixels, 0, width );
         
      // Copy the pixels to the array.
      try {
         pg.grabPixels();
      
         // Check for error using bit values in the ImageObserver class.
         if ( ( pg.getStatus() & ImageObserver.ABORT ) != 0 )
            return;
            
         // If successful, set instance attributes to legitimate values (not –1).
         mWidth = width;
         mHeight = height;
      }
      catch ( InterruptedException e ) {
         return;
      }
   }

   // For a task that may take some time, it helps to wrap it in a separate method or
   // even class, and spin it off as a thread. Here, simply get the current progress
   // and display it.
   protected void performTask() {
      int percentComplete = 0;
      
      boolean taskComplete = false;
      
      while ( !taskComplete ) {
         // Call the native method that draws the progress bar.
         updateProgressBar( percentComplete );
         
         percentComplete = updateTask();
         
         if ( percentComplete >= 100 )
            taskComplete = true;
      }
   }

   int mCount = 0;
   
   // Lengthy tasks will use a sophisticated approach to determining completion.
   // This example uses a simple loop so we can watch the bar move.
   protected int updateTask() {
      return mCount++;
   }
}

class LocalFile {
   FileDialog mFileDialog = null;
   
   // Display a dialog asking the user to choose a file.
   public LocalFile() {
      if ( mFileDialog == null ) {
         mFileDialog = new FileDialog( new Frame(), 
            “Select an image file”, FileDialog.LOAD );
      }
   }
   
   // Build and return the path to the file (if selected).
   public String getFilePath() {
      mFileDialog.setVisible( true );
      
      String retval = “”;
      
      if ( mFileDialog.getFile() != null && 
         mFileDialog.getFile().length() > 0 ) {
         retval = mFileDialog.getDirectory();
         
         if ( !retval.endsWith( 
            System.getProperty( “file.separator” ) ) )
            retval += System.getProperty( “file.separator” );
         
         retval += mFileDialog.getFile();
      }
      
      return retval;
   }
}

// A subclass of java.awt.Canvas that draws an Image object.
class PictureFrame extends Canvas {
   Image mImage;
   
   PictureFrame( Image img ) {
      super();
      mImage = img;
      setBackground( Color.white );
   }
   
   public void update( Graphics g ) {
      paint( g );
   }
   
   // Draw the image.
   public void paint( Graphics g ) {
      g.drawImage( mImage, 0, 0, this );
   }
}

Java Native Interface Code

JNI code is C code that bridges the Java and native worlds, handling the conversion between Java data types and their native counterparts. The JNIEnv pointer in each function indirectly points to a function table containing JNI functions, and the jobject references the instance of the class making the call. Any additional arguments are the values passed from the Java code to the native code.

Listing 2: ExampleJNILib.c

ExampleJNILib
The JNI glue for converting arguments prior to calling through to the native code.

#include “JNISample.h”
#include “ExampleDylib.h”

JNIEXPORT void JNICALL Java_DockTiler_setDockTile( 
   JNIEnv *env, jobject this, jintArray pixels, jint width, 
   jint height ) {
   // Obtain a pointer to the array to pass to the native function.
   jint *theArray = (*env)->GetIntArrayElements( 
      env, pixels, NULL );

   if ( theArray != NULL ) {
      // Call the library function.
      // Note that no adjustments are made to the primitive values.
      setDockTile( theArray, width, height );
  
      // Tell the VM we are no longer interested in the array.
      (*env)->ReleaseIntArrayElements( env, pixels, theArray, 
         0 );
   }
}

JNIEXPORT void JNICALL Java_DockTiler_updateProgressBar( 
   JNIEnv *env, jobject this, jint currPercent ) {
   // Call the library function.
   // No additional translation is needed on primitive values.
   updateProgressBar( currPercent );
}

The Library

The native library contains the actual tile drawing code. One function creates an image and replaces the existing tile with the new one. The second function uses a completion percentage value to determine how much of the progress bar to paint. It draws over the bottom of the existing tile.

Listing 3: ExampleDylib.c

ExampleDylib.c
Perform drawing in the Dock tile.

#include 
#include 
#include 

// Args include the array of pixel RGBA values, and the actual image width and height.
extern void setDockTile( int * imagePixels, int width, 
   int height ) {
   // How many bytes in each pixel? Java uses 4-byte ints.
   int kNumComponents = 4;
   
   OSStatus   theError;

   // Several CoreGraphics variables.
   CGContextRef theContext;
   CGDataProviderRef theProvider;
   CGColorSpaceRef theColorspace;
   CGImageRef theImage;

   // How many bytes in each row?
   size_t bytesPerRow = width * kNumComponents;

   // Obtain graphics context in which to render.
   theContext = BeginCGContextForApplicationDockTile();

   if ( theContext != NULL ) {   
      // Use the pixels passed in as the image source.
      theProvider = CGDataProviderCreateWithData( 
         NULL, imagePixels, ( bytesPerRow * height ), NULL );
   
      theColorspace = CGColorSpaceCreateDeviceRGB();
      
      // Create the image. This is similar to creating a PixMap. 
      // - The width and height were passed as arguments. 
      // - The next two values (8 and 32) are the bits per pixel component and 
      //    total bits per pixel, respectively. 
      // - bytesPerRow was calculated above. 
      // - Use the colorspace ref obtained previously. 
      // - The alpha or transparency data is in the first byte of each pixel. 
      // - Use the data source created a few lines above.
      // - The remaining parameters are typical defaults. Consult the API docs for 
      //    more info.
      theImage = CGImageCreate( width, height, 8, 32, 
         bytesPerRow, theColorspace, kCGImageAlphaFirst, 
         theProvider, NULL, 0, kCGRenderingIntentDefault );
   
      CGDataProviderRelease( theProvider );
      CGColorSpaceRelease( theColorspace );
      
      // Set the created image as the tile.
      theError = SetApplicationDockTileImage( theImage );

      CGContextFlush( theContext );
   
      CGImageRelease( theImage );

      EndCGContextForApplicationDockTile( theContext );
   }
}

extern void updateProgressBar( const int currPercent ) {
   CgrafPtr thePort;
   Rect   theRect;
   float   right = 0;
   
   // Obtain graphics context.
   thePort = BeginQDContextForApplicationDockTile();

   if ( thePort != NULL ) {
      // Good ol’ QuickDraw.
      GetPortBounds( thePort, &theRect );
      
      // Initially, draw the background of the bar and frame it.
      if ( currPercent == 0 ) {
         SetRect( &theRect, theRect.left, theRect.bottom - 10, 
            theRect.right, theRect.bottom );
         ForeColor( redColor );
         PaintRect( &theRect );
         ForeColor( blackColor );
         FrameRect( &theRect );
      }
      
      // Calculate right-edge of progress bar.
      if ( currPercent >= 100 )
         right = ( float )theRect.right;
      else
         right = ( ( ( float )theRect.right – 
            ( float )theRect.left ) / 
            ( float )100 ) * ( float )currPercent;

      // Draw the entire progress bar up until this point.
      ForeColor( greenColor );

      // Inset the progress rectangle on our own.
      SetRect( &theRect, theRect.left + 1, 
         theRect.bottom - 9, ( int )right, 
         theRect.bottom - 1 );

      PaintRect( &theRect );

      QDFlushPortBuffer( thePort, NULL );

      EndQDContextForApplicationDockTile( thePort );
   }
}

The image creation using the CoreGraphics API is the trickiest part. This example uses the fact that a Java int is 4 bytes, and that alpha (transparency) data, if included, is stored in the most significant byte. After some trial and error, I found that the settings shown here work for the images I tested against.

Useful URLs

I used quite a few outside sources (primarily Apple) in preparing this article. Though some of these URLs may change, I want to at least point you in the right direction.


Andrew has been a Java fan since his first encounter with the language at the WebEdge III conference in 1996. You can reach him at andrew@downs.ws.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Pinegrow 4 - Mockup and design webpages...
Pinegrow (was Pinegrow Web Designer) is desktop app that lets you mockup and design webpages faster with multi-page editing, CSS and LESS styling, and smart components for Bootstrap, Foundation,... Read more
iExplorer 4.1.11 - View and transfer fil...
iExplorer is an iPhone browser for Mac lets you view the files on your iOS device. By using a drag and drop interface, you can quickly copy files and folders between your Mac and your iPhone or... Read more
Evernote 6.13.1 - Create searchable note...
Evernote allows you to easily capture information in any environment using whatever device or platform you find most convenient, and makes this information accessible and searchable at anytime, from... Read more
Myriad 4.2.1 - Audio batch processor.
Myriad is, simply put, one of the best audio batch processors. Totally redesigned, it looks beautiful and delivers incredible performance. Let Myriad do the heavy lifting while you get back to doing... Read more
Garmin Express 5.8.0.0 - Manage your Gar...
Garmin Express is your essential tool for managing your Garmin devices. Update maps, golf courses and device software. You can even register your device. Update maps Update software Register your... Read more
Arq 5.10 - Online backup to Google Drive...
Arq is super-easy online backup for Mac and Windows computers. Back up to your own cloud account (Amazon Cloud Drive, Google Drive, Dropbox, OneDrive, Google Cloud Storage, any S3-compatible server... Read more
Garmin Express 5.8.0.0 - Manage your Gar...
Garmin Express is your essential tool for managing your Garmin devices. Update maps, golf courses and device software. You can even register your device. Update maps Update software Register your... Read more
Myriad 4.2.1 - Audio batch processor.
Myriad is, simply put, one of the best audio batch processors. Totally redesigned, it looks beautiful and delivers incredible performance. Let Myriad do the heavy lifting while you get back to doing... Read more
Arq 5.10 - Online backup to Google Drive...
Arq is super-easy online backup for Mac and Windows computers. Back up to your own cloud account (Amazon Cloud Drive, Google Drive, Dropbox, OneDrive, Google Cloud Storage, any S3-compatible server... Read more
Evernote 6.13.1 - Create searchable note...
Evernote allows you to easily capture information in any environment using whatever device or platform you find most convenient, and makes this information accessible and searchable at anytime, from... Read more

Latest Forum Discussions

See All

warbot.io wants you for the robot wars
Fans of epic gundam-style battles will find a lot to love in warbot.io, the first game for up and coming developer Wondersquad. The game saw a lot of success when it first launched for browsers and Facebook, and now even more people are getting the... | Read more »
Uncover alien mysteries in cross-genre s...
If the Alien franchise taught us anything, it’s that landing on a strange planet at the behest of a faceless corporation is probably asking for trouble. And Eldritch Game’s Deliria doesn’t prove otherwise. In 2107, Dimension LG7 is rich with... | Read more »
The best mobile games to play during dre...
| Read more »
The mobile gamer's guide to Black F...
We're starting to catch wind of some exciting deals in the mobile gaming space for Black Friday. There are big discounts on mobile phones and accessories cropping up already, so you might want to get a move on things ahead of the big day. It's... | Read more »
The best pre-Black Friday deals - Novemb...
Black Friday will soon be upon us, but online retailers are already getting a headstart on the steep discounts. Don't wait until Friday—you'll find some pretty good deals all over the internet without waiting in lines or competing with other... | Read more »
Mighty Battles guide - how to build a so...
Mighty Battles, the latest title from Hothead Games, is set to take the App Store by storm. The game puts a welcome twist on lane battlers, adding FPS elements to spice things up a bit. You'll collect cards to put your own military unit to gether,... | Read more »
Rules of Survival guide - how to be the...
The PUBG craze makes its way to mobile, with more and more battle royale games debuting on iOS and Android. Rules of Survival joins the ranks of mobile PUBG-likes, offering a classic battle royale experiences that doesn't vary too much from its... | Read more »
The best new games we played this week -...
The weekend is upon us friends, and it's time to take a look back and reflect on all of the wonderful games we've played over the past few days. This week was jam packed with new releases. There were some big, long awaited launches, some fun... | Read more »
Lineage II: Revolution guide - tips and...
At long last, Lineage II: Revolution has now come to western shores, bring Netmarble's sweeping MMORPG to mobile devices. It's an addictive, epic experience, but some of the systems in the game can be a bit overwhelming. Here are a few tips to help... | Read more »
A Boy and His Blob (Games)
A Boy and His Blob 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: | Read more »

Price Scanner via MacPrices.net

Lowest Black Friday prices on Apple MacBooks:...
Save $150-$420 on the purchase of a MacBook Pro, MacBook, or MacBook Air this Black Friday and Holiday weekend with Certified Refurbished models at Apple. In many cases, Apple’s refurbished prices... Read more
Black Friday: Apple Watch Series 1 for $70 of...
Macy’s has discounted Series 1 Apple Watches by $70 on their online store as part of their Black Friday sale: – 38mm Series 1 Apple Watch: $179, $70 off – 42mm Series 1 Apple Watch: $209, $70 off... Read more
Apple offers 2016 13-inch MacBook Airs, certi...
Apple has Certified Refurbished 2016 13″ MacBook Airs available starting at $809. An Apple one-year warranty is included with each MacBook, and shipping is free: – 13″ 1.6GHz/8GB/128GB MacBook Air: $... Read more
Black Friday sale: Mac minis for $100 off MSR...
B&H Photo has Mac minis on sale for up to $100 off MSRP as part of their Black Friday sale, each including free shipping plus NY & NJ sales tax only: – 1.4GHz Mac mini: $399 $100 off MSRP – 2... Read more
Use your Apple Education discount to save up...
Purchase a new Mac using Apple’s Education discount, and take up to $300 off MSRP. All teachers, students, and staff of any educational institution with a .edu email address qualify for the discount... Read more
Adorama posts Black Friday deals on Apple Mac...
Adorama has posted Black Friday sale prices on many Macs, with MacBooks and iMacs available for up to $200 off MSRP. Shipping is free, and Adorama charges sales tax in NJ and NY only: MacBook Pros... Read more
Save up to $300 on 15″ 2.2GHz MacBook Pros
B&H Photo has the 15″ 2.2GHz MacBook Pro available for $200 off MSRP including free shipping plus NY & NJ sales tax only: – 15″ 2.2GHz MacBook Pro (MJLQ2LL/A): $1799 $200 off MSRP Amazon.com... Read more
Save up to $180 with Apple Certified Refurbis...
Apple has Certified Refurbished 2017 13″ MacBook Airs available starting at $849. An Apple one-year warranty is included with each MacBook, and shipping is free: – 13″ 1.8GHz/8GB/128GB MacBook Air (... Read more
Black Friday deals on Apple Macs now live at...
Amazon has MacBook Pros, MacBook Airs, MacBooks, and iMacs on sale for up to $200 off MSRP for Black Friday week. Shipping is free. Note that stock of some Macs may come and go during the week, so... Read more
Black Friday pricing on Macs and iPads now av...
B&H Photo has lowered prices on many Macs, iPads, and iPad Pros as part of their Black Friday week sale. Save up to $200 on MacBooks and iMacs and up to $150 on iPads. B&H charges sales tax... Read more

Jobs Board

*Apple* Professional Learning Specialist - A...
# Apple Professional Learning Specialist Job Number: 112953711 Houston, Texas, United States Posted: 07-Sep-2017 Weekly Hours: 40.00 **Job Summary** The Apple Read more
*Apple* Retail - Multiple Positions - Apple,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
Product Manager - *Apple* Pay on the *Appl...
Job Summary Apple is looking for a talented product manager to drive the expansion of Apple Pay on the Apple Online Store. This position includes a unique Read more
*Apple* Pro/Consumer Apps Support Engineer -...
…exemplify AppleCare's expert technical support paired with exceptional customer service for Apple 's software apps. This person is a problem solver, who understands Read more
Partner Marketing Manager, *Apple* Pay - Ap...
Job Summary The Apple Pay partner marketing team is looking for a Marketing Manager to develop and drive US programs. The right candidate will be passionate about Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.