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

NetShade 6.3.1 - Browse privately using...
NetShade is an anonymous proxy and VPN app+service for Mac. Unblock your Internet through NetShade's high-speed proxy and VPN servers spanning seven countries. NetShade masks your IP address as you... Read more
Dragon Dictate 4.0.7 - Premium voice-rec...
With Dragon Dictate speech recognition software, you can use your voice to create and edit text or interact with your favorite Mac applications. Far more than just speech-to-text, Dragon Dictate lets... Read more
Persecond 1.0.2 - Timelapse video made e...
Persecond is the easy, fun way to create a beautiful timelapse video. Import an image sequence from any camera, trim the length of your video, adjust the speed and playback direction, and you’re done... Read more
GIMP 2.8.14p2 - Powerful, free image edi...
GIMP is a multi-platform photo manipulation tool. GIMP is an acronym for GNU Image Manipulation Program. The GIMP is suitable for a variety of image manipulation tasks, including photo retouching,... Read more
Sandvox 2.10.2 - Easily build eye-catchi...
Sandvox is for Mac users who want to create a professional looking website quickly and easily. With Sandvox, you don't need to be a Web genius to build a stylish, feature-rich, standards-compliant... Read more
LibreOffice 5.0.1.2 - Free, open-source...
LibreOffice is an office suite (word processor, spreadsheet, presentations, drawing tool) compatible with other major office suites. The Document Foundation is coordinating development and... Read more
f.lux 36.1 - Adjusts the color of your d...
f.lux makes the color of your computer's display adapt to the time of day, warm at night and like sunlight during the day. Ever notice how people texting at night have that eerie blue glow? Or wake... Read more
VirtualBox 5.0.2 - x86 virtualization so...
VirtualBox is a family of powerful x86 virtualization products for enterprise as well as home use. Not only is VirtualBox an extremely feature rich, high performance product for enterprise customers... Read more
File Juicer 4.43 - Extract images, video...
File Juicer is a drag-and-drop can opener and data archaeologist. Its specialty is to find and extract images, video, audio, or text from files which are hard to open in other ways. In computer... Read more
Apple MainStage 3.2 - Live performance t...
MainStage 3 makes it easy to bring to the stage all the same instruments and effects that you love in your recording. Everything from the Sound Library and Smart Controls you're familiar with from... Read more

ReBoard: Revolutionary Keyboard (Utilit...
ReBoard: Revolutionary Keyboard 1.0 Device: iOS Universal Category: Utilities Price: $1.99, Version: 1.0 (iTunes) Description: Do everything within the keyboard without switching apps! If you are in WhatsApp, how do you schedule a... | Read more »
Tiny Empire (Games)
Tiny Empire 1.1.3 Device: iOS Universal Category: Games Price: $2.99, Version: 1.1.3 (iTunes) Description: Launch cannonballs and blow tiny orcs into thousands of pieces in this intuitive fantasy-themed puzzle shooter! Embark on an... | Read more »
Astropad Mini (Productivity)
Astropad Mini 1.0 Device: iOS iPhone Category: Productivity Price: $4.99, Version: 1.0 (iTunes) Description: *** 50% off introductory price! ​*** Get the high-end experience of a Wacom tablet at a fraction of the price with Astropad... | Read more »
Emo Chorus (Music)
Emo Chorus 1.0.0 Device: iOS Universal Category: Music Price: $1.99, Version: 1.0.0 (iTunes) Description: Realistic Choir simulator ranging from simple Chorus emulation to full ensemble Choir with 128 members. ### introductory offer... | Read more »
Forest Spirit (Games)
Forest Spirit 1.0.5 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0.5 (iTunes) Description: | Read more »
Ski Safari 2 (Games)
Ski Safari 2 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: The world's most fantastical, fun, family-friendly skiing game is back and better than ever! Play as Sven's sister Evana, share... | Read more »
Lara Croft GO (Games)
Lara Croft GO 1.0.47768 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0.47768 (iTunes) Description: Lara Croft GO is a turn based puzzle-adventure set in a long-forgotten world. Explore the ruins of an ancient... | Read more »
Whispering Willows (Games)
Whispering Willows 1.23 Device: iOS Universal Category: Games Price: $4.99, Version: 1.23 (iTunes) Description: **LAUNCH SALE 50% OFF** - Whispering Willows is on sale for 50% off ($4.99) until September 9th. | Read more »
Calvino Noir (Games)
Calvino Noir 1.1 Device: iOS iPhone Category: Games Price: $3.99, Version: 1.1 (iTunes) Description: The film noir stealth game. Calvino Noir is the exploratory, sneaking adventure through the 1930s European criminal underworld.... | Read more »
Angel Sword (Games)
Angel Sword 1.0 Device: iOS Universal Category: Games Price: $6.99, Version: 1.0 (iTunes) Description: Prepare to adventure in the most epic full scale multiplayer 3D RPG for mobile! Experience amazing detailed graphics in full HD.... | Read more »

Price Scanner via MacPrices.net

Big Grips Lift Handle For iPad Air and iPad A...
KEM Ventures, Inc. which pioneered the extra-large, super-protective iPad case market with the introduction of Big Grips Frame and Stand in 2011, is launching Big Grips Lift featuring a new super-... Read more
Samsung Launches Galaxy Tab S2, Its Most Powe...
Samsung Electronics America, Inc. has announced the U.S. release of the Galaxy Tab S2, its thinnest, lightest, ultra-fast tablet. Blending form and function, elegant design and multitasking power,... Read more
Tablet Screen Sizes Expanding as iPad Pro App...
Larger screen sizes are gaining favor as the tablet transforms into a productivity device, with shipments growing 185 percent year-over-year in 2015. According to a new Strategy Analytics’ Tablet... Read more
Today Only: Save US$50 on Adobe Elements 13;...
Keep the memories. lose the distractions. Summer’s winding down and it’s time to turn almost perfect shots into picture perfect memories with Elements 13. And get the power to edit both photos and... Read more
1.4GHz Mac mini on sale for $449, save $50
Best Buy has the 1.4GHz Mac mini on sale for $50 off MSRP on their online store. Choose free shipping or free local store pickup (if available). Price for online orders only, in-store price may vary... Read more
12-inch 1.1GHz Gold MacBook on sale for $1149...
B&H Photo has the 12″ 1.1GHz Gold Retina MacBook on sale for $1149.99 including free shipping plus NY sales tax only. Their price is $150 off MSRP, and it’s the lowest price available for this... Read more
27-inch 3.3GHz 5K iMac on sale for $1849, sav...
Best Buy has the 27″ 3.3GHz 5K iMac on sale for $1849.99. Their price is $150 off MSRP, and it’s the lowest price available for this model. Choose free shipping or free local store pickup (if... Read more
Worldwide Tablet Shipments Expected to Declin...
Does Apple badly need a touchscreen convertible/hybrid laptop MacBook? Yes, judging from a new market forecast from the International Data Corporation (IDC) Worldwide Quarterly Tablet Tracker, which... Read more
Continued PC Shipment Shrinkage Expected Thro...
Worldwide PC shipments are expected to fall by -8.7 percent in 2015 and not stabilize until 2017, according to the latest International Data Corporation (IDC) Worldwide Quarterly PC Tracker data. The... Read more
Imminent iPhone 6s Announcement Leads To 103%...
NextWorth Solutions, with its online and in-store electronics trade-in programs including http://NextWorth.com, reports that it has experienced a 103 percent surge in quoted trade-in values over the... Read more

Jobs Board

*Apple* Retail Online Store: Customer Insigh...
**Job Summary** Apple Retail (Online Store) is seeking an experienced e-commerce analytics professional to join the Customer Insights Team. The Web e-Commerce Analyst Read more
*Apple* Music, Business Operations - Apple I...
Changing the world is all in a day039s work at Apple . If you love innovation, here039s your chance to make a career of it. You039ll work hard. But the job comes with Read more
WW *Apple* Retail Online Store: Customer In...
**Job Summary** The Apple Retail - Online Store is seeking an experienced web merchandising analytics professional to join the Customer Insights Team. The Web Read more
Senior Payments Security Manager - *Apple*...
**Job Summary** Apple , Inc. is looking for a highly motivated, innovative and hands-on senior payments security manager to join the Apple Pay security team. You will Read more
Software QA Engineer, *Apple* Pay Security...
**Job Summary** Imagine what you could do here. At Apple , great ideas have a way of becoming great products, services, and customer experiences very quickly. Bring Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.