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.

 
AAPL
$119.00
Apple Inc.
+1.40
MSFT
$47.75
Microsoft Corpora
+0.28
GOOG
$540.37
Google Inc.
-0.71

MacTech Search:
Community Search:

Software Updates via MacUpdate

Skype 7.2.0.412 - Voice-over-internet ph...
Skype allows you to talk to friends, family and co-workers across the Internet without the inconvenience of long distance telephone charges. Using peer-to-peer data transmission technology, Skype... Read more
HoudahSpot 3.9.6 - Advanced file search...
HoudahSpot is a powerful file search tool built upon MacOS X Spotlight. Spotlight unleashed Create detailed queries to locate the exact file you need Narrow down searches. Zero in on files Save... Read more
RapidWeaver 6.0.3 - Create template-base...
RapidWeaver is a next-generation Web design application to help you easily create professional-looking Web sites in minutes. No knowledge of complex code is required, RapidWeaver will take care of... Read more
iPhoto Library Manager 4.1.10 - Manage m...
iPhoto Library Manager lets you organize your photos into multiple iPhoto libraries. Separate your high school and college photos from your latest summer vacation pictures. Or keep some photo... Read more
iExplorer 3.5.1.9 - View and transfer al...
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
MacUpdate Desktop 6.0.3 - Discover and i...
MacUpdate Desktop 6 brings seamless 1-click installs and version updates to your Mac. With a free MacUpdate account and MacUpdate Desktop 6, Mac users can now install almost any Mac app on macupdate.... Read more
SteerMouse 4.2.2 - Powerful third-party...
SteerMouse is an advanced driver for USB and Bluetooth mice. It also supports Apple Mighty Mouse very well. SteerMouse can assign various functions to buttons that Apple's software does not allow,... Read more
iMazing 1.1 - Complete iOS device manage...
iMazing (was DiskAid) is the ultimate iOS device manager with capabilities far beyond what iTunes offers. With iMazing and your iOS device (iPhone, iPad, or iPod), you can: Copy music to and from... Read more
PopChar X 7.0 - Floating window shows av...
PopChar X helps you get the most out of your font collection. With its crystal-clear interface, PopChar X provides a frustration-free way to access any font's special characters. Expanded... Read more
OneNote 15.4 - Free digital notebook fro...
OneNote is your very own digital notebook. With OneNote, you can capture that flash of genius, that moment of inspiration, or that list of errands that's too important to forget. Whether you're at... Read more

Latest Forum Discussions

See All

Raby (Games)
Raby 1.0.3 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0.3 (iTunes) Description: ***WARNING - Raby runs on: iPhone 5, iPhone 5C, iPhone 5S, iPhone 6, iPhone 6 Plus, iPad Mini Retina, iPad Mini 3, iPad 4, iPad Air,... | Read more »
Oddworld: Stranger's Wrath (Games)
Oddworld: Stranger's Wrath 1.0 Device: iOS Universal Category: Games Price: $5.99, Version: 1.0 (iTunes) Description: ** PLEASE NOTE: Oddworld Stranger's Wrath requires at least an iPhone 4S, iPad 2, iPad Mini or iPod Touch 5th gen... | Read more »
Bounce On Back (Games)
Bounce On Back 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: | Read more »
Dwelp (Games)
Dwelp 1.0 Device: iOS Universal Category: Games Price: $.99, Version: 1.0 (iTunes) Description: === 50% off for a limited time, to celebrate release === Dwelp is an elegant little puzzler with a brand new game mechanic. To complete a... | Read more »
Make Way for Fat Chicken, from the Maker...
Make Way for Fat Chicken, from the Makers of Scrap Squad Posted by Jessica Fisher on November 26th, 2014 [ permalink ] Relevant Games has announced they will be releasing their reverse tower defense game, | Read more »
Tripnary Review
Tripnary Review By Jennifer Allen on November 26th, 2014 Our Rating: :: TRAVEL BUCKET LISTiPhone App - Designed for the iPhone, compatible with the iPad Want to create a travel bucket list? Tripnary is a fun way to do exactly that... | Read more »
Ossian Studios’ RPG, The Shadow Sun, is...
Ossian Studios’ RPG, The Shadow Sun, is Now Available for $4.99 Posted by Jessica Fisher on November 26th, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Mmmm, Tasty – Having the Angry Birds for...
The very first Angry Birds debuted on iOS back in 2009. When you sit back and tally up the number of Angry Birds games out there and the impact they’ve had on pop culture as a whole, you just need to ask yourself: “How would the birds taste... | Read more »
Rescue Quest Review
Rescue Quest Review By Jennifer Allen on November 26th, 2014 Our Rating: :: PATH BASED MATCH-3Universal App - Designed for iPhone and iPad Guide a wizard to safety by matching gems. Rescue Quest might not be an entirely original... | Read more »
You Can Play the Final Chapter of Lone W...
You Can Play the Final Chapter of Lone Wolf: Dawn Over V’taag Right Now Posted by Jessica Fisher on November 26th, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »

Price Scanner via MacPrices.net

Black Friday: $300 off 15-inch Retina MacBook...
 B&H Photo has the new 2014 15″ Retina MacBook Pros on sale for $300 off MSRP as part of their Black Friday sale. Shipping is free, and B&H charges NY sales tax only: - 15″ 2.2GHz Retina... Read more
2014 1.4GHz Mac mini on sale for $449, save $...
 B&H Photo has the new 1.4GHz Mac mini on sale for $449.99 including free shipping plus NY tax only. Their price is $50 off MSRP, and it’s the lowest price available for this new model. Adorama... Read more
Early Black Friday pricing on 27-inch 5K iMac...
 B&H Photo continues to offer Black Friday sale prices on the 27″ 3.5GHz 5K iMac, in stock today and on sale for $2299 including free shipping plus NY sales tax only. Their price is $200 off MSRP... Read more
Early Black Friday sale prices on iPad Air 2,...
 MacMall is discounting iPad Air 2s by up to $75 off MSRP as part of their Black Friday sale. Shipping is free: - 16GB iPad Air WiFi: $459 $40 off - 64GB iPad Air WiFi: $559 $40 off - 128GB iPad Air... Read more
Early Black Friday MacBook Air sale prices, $...
 MacMall has posted early Black Friday MacBook Air sale prices. Save $101 on all models for a limited time: - 11″ 1.4GHz/128GB MacBook Air: $798 - 11″ 1.4GHz/256GB MacBook Air: $998 - 13″ 1.4GHz/... Read more
Why iPhone 6 Tablet/Laptop Cannibalization Is...
247wallst.com blogger Douglas A. McIntyre noted last week that according to research posted on the Applovin blog site the iPhone 6 is outselling the iPhone 6 Plus by a wide margin . Hardly a surprise... Read more
Worldwide Tablet Growth Expected to Slow to 7...
The global tablet market is expected to record massive deceleration in 2014 with year-over-year growth slowing to 7.2%, down from 52.5% in 2013, according to a new forecast from International Data... Read more
Touchscreen Glove Company Announces New Produ...
Surrey, United Kingdom based TouchAbility specializes in design and manufacture of a wide variety of products compatible with touchscreen devices including smartphones, tablets and computers. Their... Read more
OtterBox Alpha Glass Screen Protectors for iP...
To complement the bigger, sharper displays on the latest Apple devices, OtterBox has introduced Alpha Glass screen protectors to the iPhone 6 and iPhone 6 Plus. The fortified glass screen protectors... Read more
Early Black Friday Mac Pro sale, 6-Core 3.5GH...
 B&H Photo has the 6-Core 3.5GHz Mac Pro on sale today for $3499 including free shipping plus NY sales tax. Their price is $500 off MSRP, and it’s the lowest price available for this model from... Read more

Jobs Board

*Apple* Solutions Consultant (ASC) - Apple (...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
Senior Event Manager, *Apple* Retail Market...
…This senior level position is responsible for leading and imagining the Apple Retail Team's global event strategy. Delivering an overarching brand story; in-store, Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Solutions Consultant (ASC) - Apple (...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
*Apple* Solutions Consultant (ASC) - Apple (...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.