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Inside the Animated Cursor Library, Part 2

The second animated cursor library implementation consists of a main ca.mb.javajeff.anicursor package that depends on three support packages—in addition to ca.mb.javajeff.riff and ca.mb.javajeff.cur, a ca.mb.javajeff.ico support package is used by the second implementation. Listing 4 presents the source code to the main package’s AniCursor class.

Listing 4 AniCursor.java.

// AniCursor.java

// Create an animated cursor based on a Microsoft .ani file.

package ca.mb.javajeff.anicursor;

import java.awt.*;
import java.awt.image.*;

import java.io.*;

import java.util.*;

import javax.swing.*;

import ca.mb.javajeff.cur.*;
import ca.mb.javajeff.ico.*;
import ca.mb.javajeff.riff.*;

public class AniCursor implements Runnable
{
  private volatile boolean finished; // Animation completion flag

  private volatile Component comp;

  private volatile Cursor [] cursors;

  private int [] durations;

  private int [] sequence;

  private int index;

  public AniCursor (String aniName, Component comp)
   throws BadAniException, IOException
  {
   this.comp = comp;

   if (aniName == null)
   {
     cursors = new Cursor [8];
     cursors [0] = Cursor.getPredefinedCursor (Cursor.N_RESIZE_CURSOR);
     cursors [1] = Cursor.getPredefinedCursor (Cursor.NE_RESIZE_CURSOR);
     cursors [2] = Cursor.getPredefinedCursor (Cursor.E_RESIZE_CURSOR);
     cursors [3] = Cursor.getPredefinedCursor (Cursor.SE_RESIZE_CURSOR);
     cursors [4] = Cursor.getPredefinedCursor (Cursor.S_RESIZE_CURSOR);
     cursors [5] = Cursor.getPredefinedCursor (Cursor.SW_RESIZE_CURSOR);
     cursors [6] = Cursor.getPredefinedCursor (Cursor.W_RESIZE_CURSOR);
     cursors [7] = Cursor.getPredefinedCursor (Cursor.NW_RESIZE_CURSOR);

     durations = new int [8];
     for (int i = 0; i < durations.length; i++)
        durations [i] = 75;

     sequence = new int [8];
     for (int i = 0; i < sequence.length; i++)
        sequence [i] = i;
   }
   else
   {
     RIFF riff = null;
     try
     {
       riff = new RIFF (aniName);
       if (!riff.getFormType ().equals ("ACON"))
         throw new BadAniException ("not an animated cursor file");

       ArrayList<BufferedImage> bilist;
       bilist = new ArrayList<BufferedImage> ();

       int x;
       int y;

       Chunk chunk;
       while ((chunk = riff.getChunk ()) != null)
         if (chunk.name.equals ("anih"))
         {
           int size = ubyte (chunk.data [3]);
           size <<= 8;
           size |= ubyte (chunk.data [2]);
           size <<= 8;
           size |= ubyte (chunk.data [1]);
           size <<= 8;
           size |= ubyte (chunk.data [0]);

           int nframes = ubyte (chunk.data [7]);
           nframes <<= 8;
           nframes |= ubyte (chunk.data [6]);
           nframes <<= 8;
           nframes |= ubyte (chunk.data [5]);
           nframes <<= 8;
           nframes |= ubyte (chunk.data [4]);

           int nsteps = ubyte (chunk.data [11]);
           nsteps <<= 8;
           nsteps |= ubyte (chunk.data [10]);
           nsteps <<= 8;
           nsteps |= ubyte (chunk.data [9]);
           nsteps <<= 8;
           nsteps |= ubyte (chunk.data [8]);

           int width = ubyte (chunk.data [15]);
           width <<= 8;
           width |= ubyte (chunk.data [14]);
           width <<= 8;
           width |= ubyte (chunk.data [13]);
           width <<= 8;
           width |= ubyte (chunk.data [12]);

           int height = ubyte (chunk.data [19]);
           height <<= 8;
           height |= ubyte (chunk.data [18]);
           height <<= 8;
           height |= ubyte (chunk.data [17]);
           height <<= 8;
           height |= ubyte (chunk.data [16]);

           int bitcount = ubyte (chunk.data [23]);
           bitcount <<= 8;
           bitcount |= ubyte (chunk.data [22]);
           bitcount <<= 8;
           bitcount |= ubyte (chunk.data [21]);
           bitcount <<= 8;
           bitcount |= ubyte (chunk.data [20]);

           int nplanes = ubyte (chunk.data [27]);
           nplanes <<= 8;
           nplanes |= ubyte (chunk.data [26]);
           nplanes <<= 8;
           nplanes |= ubyte (chunk.data [25]);
           nplanes <<= 8;
           nplanes |= ubyte (chunk.data [24]);

           int disprate = ubyte (chunk.data [31]);
           disprate <<= 8;
           disprate |= ubyte (chunk.data [30]);
           disprate <<= 8;
           disprate |= ubyte (chunk.data [29]);
           disprate <<= 8;
           disprate |= ubyte (chunk.data [28]);

           int attr = ubyte (chunk.data [35]);
           attr <<= 8;
           attr |= ubyte (chunk.data [34]);
           attr <<= 8;
           attr |= ubyte (chunk.data [33]);
           attr <<= 8;
           attr |= ubyte (chunk.data [32]);

           if ((attr & 1) == 0)
             throw new BadAniException ("cannot deal with raw "+
                          "bitmap data");
           durations = new int [nsteps];
           for (int i = 0; i < durations.length; i++)
             durations [i] = disprate*1000/60; // convert from
                              // jiffies to
                              // milliseconds

           sequence = new int [nsteps];
           for (int i = 0; i < sequence.length; i++)
             sequence [i] = i;
         }
         else
         if (chunk.name.equals ("icon"))
         {
           BufferedImage bi;
           int ncolors;

           if (chunk.data [2] == 1 && chunk.data [3] == 0)
           {
             Ico i;
             try
             {
               i = new Ico (new ByteArrayInputStream (chunk.data));
             }
             catch (BadIcoResException bire)
             {
               throw new BadAniException (bire);
             }
             bi = i.getImage (0);
             ncolors = i.getNumColors (0);
             x = 0;
             y = 0;
           }
           else
           if (chunk.data [2] == 2 && chunk.data [3] == 0)
           {
             Cur c;
             try
             {
               c = new Cur (new ByteArrayInputStream (chunk.data));
             }
             catch (BadCurResException bcre)
             {
               throw new BadAniException (bcre);
             }
             bi = c.getImage (0);
             ncolors = c.getNumColors (0);
             x = c.getHotspotX (0);
             y = c.getHotspotY (0);
           }
           else
            throw new BadAniException ("icon or cursor resource "+
                          "expected");

           // Convert a translucent alpha channel, where alpha
           // ranges from 0 to 255, to a binary alpha channel, where
           // alpha is either 0 or 255.

           if (ncolors == 0)
             for (int i = 0; i < bi.getHeight (); i++)
             {
               int [] rgb = bi.getRGB (0, i, bi.getWidth (), 1,
                           null, 0,
                           bi.getWidth ()*4);
               for (int j = 0; j < rgb.length; j++)
               {
                  int alpha = (rgb [j] >> 24) & 255;
                  if (alpha < 0x80)
                    alpha = 0;
                  else
                    alpha = 255;
                  rgb [j] &= 0x00ffffff;
                  rgb [j] = (alpha << 24) | rgb [j];
               }
               bi.setRGB (0, i, bi.getWidth (), 1, rgb, 0,
                     bi.getWidth ()*4);
             }
           bilist.add (bi);

           cursors = new Cursor [bilist.size ()];

           Toolkit toolkit = Toolkit.getDefaultToolkit ();
           for (int i = 0; i < bilist.size (); i++)
             cursors [i] = toolkit.
                    createCustomCursor (bilist.get (i),
                              new Point (x, y),
                              "anicursor");
         }
         else
         if (chunk.name.equals ("rate"))
         {
           if (durations == null)
             throw new BadAniException ("ANI header missing");

           for (int i = 0; i < durations.length; i++)
           {
             int rate = ubyte (chunk.data [4*i+3]);
             rate <<= 8;
             rate |= ubyte (chunk.data [4*i+2]);
             rate <<= 8;
             rate |= ubyte (chunk.data [4*i+1]);
             rate <<= 8;
             rate |= ubyte (chunk.data [4*i]);

             durations [i] = rate*1000/60; // convert from jiffies
                            // to milliseconds
           }
         }
         else
         if (chunk.name.equals ("seq "))
         {
           if (sequence == null)
             throw new BadAniException ("ANI header missing");

           for (int i = 0; i < sequence.length; i++)
           {
             int index = ubyte (chunk.data [4*i+3]);
             index <<= 8;
             index |= ubyte (chunk.data [4*i+2]);
             index <<= 8;
             index |= ubyte (chunk.data [4*i+1]);
             index <<= 8;
             index |= ubyte (chunk.data [4*i]);

             sequence [i] = index;
           }
         }
     }
     catch (BadRIFFException briffe)
     {
       throw new BadAniException (briffe);
     }
     finally
     {
       if (riff != null)
         riff.close ();
     }

     if (durations == null)
       throw new BadAniException ("ANI header missing");
   }
  }

  public void run ()
  {
   index = 0;

   Runnable r = new Runnable ()
          {
            public void run ()
            {
              comp.setCursor (cursors [sequence [index]]);
            }
          };

   while (!finished)
   {
     try
     {
       Thread.currentThread ().sleep (durations [index]);
       SwingUtilities.invokeAndWait (r);
       index++;
       if (index == durations.length)
         index = 0;
     }
     catch (Exception ex)
     {
     }
   }

   try
   {
     r = new Runnable ()
       {
         public void run ()
         {
           comp.setCursor (Cursor.
                   getPredefinedCursor (Cursor.
                             DEFAULT_CURSOR));
         }
       };
     SwingUtilities.invokeAndWait (r);
   }
   catch (Exception ex)
   {
   }
  }

  public void start ()
  {
   finished = false;
   new Thread (this).start ();
  }

  public void stop ()
  {
   finished = true;
  }

  private int ubyte (byte b)
  {
   return (b < 0) ? 256+b : b; // Convert byte to unsigned byte.
  }
}

Although there are similarities between Listing 4 and part 1’s AniCursor.java source code, there are also differences. For example, the AniCursor source code in Listing 4 introduces two new fields: durations and sequence. These integer array fields respectively record the length of time each animation frame is displayed, and the sequence in which animation frames are shown.

AniCursor’s constructor creates and initializes durations and sequence. If the constructor’s aniName argument is null, it creates these arrays and initializes them to values that (when used together with the run() method) enable the same default cursor animation as revealed in the first part of this series.

If aniName is not null, the constructor creates both arrays and initializes them to default values extracted from the ANIHEADER data structure in response to encountering an anih chunk. Later, when the constructor encounters rate and seq chunks, it overrides these defaults with values extracted from these chunks.

The constructor extracts all field values from ANIHEADER, even field values that aren’t used. If desired, you can verify that this data structure’s size field contains 36 as an extra margin of safety. Also, you can use the width, height, bit count, and number of planes field values to extract raw bitmaps should you encounter an .ani file that stores raw bitmaps instead of cursor or icon resources.

Having reviewed the basic implementation of AniCursor in part 1, and having explored RIFF and ANI earlier in this article, I think that you’ll find Listing 4 to be pretty straightforward. However, I should discuss three items to clear up any possible confusion—always extracting only the first image from a cursor or icon resource, the cursor hotspot, and Ico versus Cur:

  • A cursor or icon resource can store multiple images; each image differs from its sibling images in terms of its width, height, and number of colors. Although one image might look better at the current display resolution than the other images, for simplicity AniCursor always extracts the first image from the resource. If you prefer to choose an image dynamically based on the current resolution, you’ll need to work with the AWT’s GraphicsEnvironment, GraphicsDevice, and DisplayMode classes to determine the current display mode; and then choose an image from the resource most appropriate for this mode.
  • AniCursor uses Toolkit’s public Cursor createCustomCursor(Image cursor, Point hotspot, String name) method to create and return a Cursor object. This method requires a reference to a Point object containing the cursor’s hotspot as one of its arguments. Because only cursor resources store hotspot information, AniCursor’s constructor extracts the hotspot associated with the first cursor image from the cursor resource and then passes this information to createCustomCursor(). For icon resources, the constructor chooses (0, 0) as a reasonable hotspot value—you might also want to choose (0, 0) if you decide to support raw bitmaps.
  • If you’ve read my article "Enhance Java GUIs with Windows Icons," you should be familiar with my ca.mb.javajeff.ico package and its Ico and BadIcoResException classes. Because I based the ca.mb.javajeff.cur.Cur class on Ico, these classes differ only in minor implementation details, and a couple of Cur methods not present in Ico that return the hotspot associated with a given cursor image. Although this similarity might give you the idea that these classes are largely interchangeable, you should only use each class with the appropriate resource type, as Listing 4 demonstrates.

This article’s implementation of the animated cursor library is located in the article’s code archive. This code is organized into multiple directories and includes part 1’s AniCursorDemo.java application source code. Follow part 1’s instructions to compile AniCursorDemo.java and the library’s source code, and to run the application with or without an .ani file command-line argument.

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