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

TotalFinder 1.12.2 - Adds tabs, hotkeys,...
TotalFinder is a universally acclaimed navigational companion for your Mac. Enhance your Mac's Finder with features so smart and convenient, you won't believe you ever lived without them. Features... Read more
Duet 2.3.0.3 - Use your iPad as an exter...
Duet is the first app that allows you to use your iDevice as an extra display for your Mac using the Lightning or 30-pin cable. Note: This app requires a $9.99 iOS companion app. Version 2.3.0.3:... Read more
FileMaker Pro Advanced 18.0.3 - Powerful...
FileMaker Pro Advanced is the tool you use to create a custom app. You also use FileMaker Pro Advanced to access your app on a computer. Start by importing data from a spreadsheet or using a built-in... Read more
OsiriX Lite 10.0.6 - 3D medical image pr...
OsiriX Lite is an image processing software dedicated to DICOM images (".dcm" / ".DCM" extension) produced by medical equipment (MRI, CT, PET, PET-CT, ...) and confocal microscopy (LSM and BioRAD-PIC... Read more
Ableton Live 10.1.5 - Record music using...
Ableton Live lets you create and record music on your Mac. Use digital instruments, pre-recorded sounds, and sampled loops to arrange, produce, and perform your music like never before. Ableton Live... Read more
Burn 2.7.8 - Easily burn data, audio, vi...
Burn... There are a lot of ways to approach burning discs. Burn keeps it simple, but still offers a lot of advanced options. Create data discs with advanced data settings like, file permissions, the... Read more
Malwarebytes 4.0.30.3073 - Adware remova...
Malwarebytes (was AdwareMedic) helps you get your Mac experience back. Malwarebytes scans for and removes code that degrades system performance or attacks your system. Making your Mac once again your... Read more
Acorn 6.5.3 - Bitmap image editor.
Acorn is a new image editor built with one goal in mind - simplicity. Fast, easy, and fluid, Acorn provides the options you'll need without any overhead. Acorn feels right, and won't drain your bank... Read more
Fantastical 2.5.13 - Create calendar eve...
Fantastical is the Mac calendar you'll actually enjoy using. Creating an event with Fantastical is quick, easy, and fun: Open Fantastical with a single click or keystroke Type in your event... Read more
A Better Finder Rename 11.05 - File, pho...
A Better Finder Rename is the most complete renaming solution available on the market today. That's why, since 1996, tens of thousands of hobbyists, professionals and businesses depend on A Better... Read more

Latest Forum Discussions

See All

Eternal Warfare is a new idle clicker fo...
Idle games are a popular genre on mobile, they might not be to everyone's taste but they're made with such regularity and receive a lot of downloads, so it's hard to argue it's not big business. Eternal Warfare is set to join the sea of idle games... | Read more »
New heroes and balance updates set to ar...
It feels like Hearthstone: Battlegrounds only launched yesterday, and already the auto batter addition to Blizzard's megahit card game is set to receive new heroes and balance updates. [Read more] | Read more »
Pre-register for Hello Kitty AR: Kawaii...
Hello Kitty — the cute cat that launched a multi-billion-pound franchise — has been brought to life… sort of. Sanrio has teamed up with the Bublar Group to create a new mobile game that uses AR tech to turn the real world into Hello Kitty’s... | Read more »
Gorgeous and tranquil puzzler Spring Fal...
One-man indie studio SPARSE//GameDev has now launched its tranquil puzzler, Spring Falls. It's described as "a peaceful puzzle game about water, erosion, and watching things grow". [Read more] | Read more »
Black Desert Mobile gets an official rel...
Pearl Abyss has just announced that its highly-anticipated MMO, Black Desert Mobile, will launch globally for iOS and Android on December 11th. [Read more] | Read more »
Another Eden receives new a episode, cha...
Another Eden, WFS' popular RPG, has received another update that brings new story content to the game alongside a few new heroes to discover. [Read more] | Read more »
Overdox guide - Tips and tricks for begi...
Overdox is a clever battle royale that changes things up by adding MOBA mechanics and melee combat to the mix. This new hybrid game can be quite a bit to take in at first, so we’ve put together a list of tips to help you get a leg up on the... | Read more »
Roterra Extreme - Great Escape is a pers...
Roterra Extreme – Great Escape has been described by developers Dig-It Games as a mini-sequel to their acclaimed title Roterra: Flip the Fairytale. It continues that game's tradition of messing with which way is up, tasking you with solving... | Read more »
Hearthstone: Battlegrounds open beta lau...
Remember earlier this year when auto battlers were the latest hotness? We had Auto Chess, DOTA Underlords, Chess Rush, and more all gunning for our attention. They all had their own reasons to play, but, at least from where I'm standing, most... | Read more »
The House of Da Vinci 2 gets a new gamep...
The House of Da Vinci launched all the way back in 2017. Now, developer Blue Brain Games is gearing up to deliver a second dose of The Room-inspired puzzling. Some fresh details have now emerged, alongside the game's first official trailer. [Read... | Read more »

Price Scanner via MacPrices.net

B&H offers $100 discounts on 4-Core and 6...
B&H Photo has new 4-Core and 6-Core Mac minis in stock and on sale today for $100 off Apple’s MSRP. Prices start at $699. Overnight shipping is free to many addresses in the US: – 3.6GHz Quad-... Read more
Save $200 today on a 2019 13″ MacBook Air wit...
Apple has a full line of Certified Refurbished 2019 13″ MacBook Airs available starting at only $929 and up to $200 off the cost of new Airs. Each MacBook features a new outer case, comes with a... Read more
New Verizon Pre-Black Friday 2019 deal: Buy o...
Buy one new Apple iPhone 11 model or 2018 iPhone XS model at Verizon and get a second one for free. One new line of service required. Offer is valid from November 21, 2019 to November 27, 2019. Here... Read more
AirPods with Wireless Charging Case on sale t...
Abt Electronics has 2019 AirPods with the Wireless Charging Case on sale today for $163 shipped. Their price is $36 off Apple’s MSRP, and it’s currently the cheapest price for these AirPods from any... Read more
Apple continues to offer 2017 13″ Dual-Core n...
Apple has Certified Refurbished 2017 13″ 2.3GHz Dual-Core non-Touch Bar MacBook Pros still available starting at $1019. An standard Apple one-year warranty is included with each model, outer cases... Read more
Save up to $120 on the new 16″ MacBook Pro at...
Apple’s resellers are starting to receive stock of new 16″ MacBook Pros, and the first set of sales & deals are now available: (1) Amazon 16″ MacBook Pros start on sale for $100-$116 off Apple’s... Read more
Apple Watch Series 3 models on sale at Amazon...
Amazon has Apple Watch Series 3 GPS models on sale for $30 off MSRP, starting at only $169. There prices are the lowest we’ve ever seen for these models from any Apple reseller. Choose Amazon as the... Read more
The ‘Mac Potpourri’ Mailbag: Edition #1- Info...
COMMENTARY: 11.20.19- Welcome to the inaugural edition of the “Mac Potpourri” Mailbag where we take a look at correspondence received from readers of this column from all over the world who write in... Read more
13″ 2.4GHz MacBook Pros available for up to $...
Apple has a full line of Certified Refurbished 2019 13″ 2.4GHz 4-Core Touch Bar MacBook Pros available starting at $1529 and up to $300 off MSRP. Apple’s one-year warranty is included, shipping is... Read more
New at T-Mobile: Switch to T-Mobile, and get...
T-Mobile is offering a free 64GB iPhone 8 for new customers who switch to T-Mobile and open a new line of service. Eligible trade-in required, and discount applied over a 24 month period. The fine... Read more

Jobs Board

Best Buy *Apple* Computing Master - Best Bu...
**747303BR** **Job Title:** Best Buy Apple Computing Master **Job Category:** Sales **Store NUmber or Department:** 001413-Cypress-Store **Job Description:** **What Read more
*Apple* Mobility Pro - Best Buy (United Stat...
**743221BR** **Job Title:** Apple Mobility Pro **Job Category:** Store Associates **Store NUmber or Department:** 000230-Greenwood-Store **Job Description:** At Best Read more
*Apple* Mobility Pro - Best Buy (United Stat...
**747338BR** **Job Title:** Apple Mobility Pro **Job Category:** Store Associates **Store NUmber or Department:** 000254-Superstition Springs-Store **Job Read more
Best Buy *Apple* Computing Master - Best Bu...
**745516BR** **Job Title:** Best Buy Apple Computing Master **Job Category:** Store Associates **Store NUmber or Department:** 001101-Manhattan-Store **Job Read more
Best Buy *Apple* Computing Master - Best Bu...
**746655BR** **Job Title:** Best Buy Apple Computing Master **Job Category:** Sales **Store NUmber or Department:** 002518-Atlantic Center-Store **Job Description:** Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.