Various improvements to decode speed and efficiency of J2ME client

git-svn-id: https://zxing.googlecode.com/svn/trunk@257 59b500cc-1b3d-0410-9834-0bbf25fbcc57

javame/src/com/google/zxing/client/j2me/AdvancedMultimediaManager.java

@@ -37,7 +37,7 @@ final class AdvancedMultimediaManager {
 
   private static final int NO_ZOOM = 100;
   private static final int MAX_ZOOM = 200;
-  private static final long FOCUS_TIME_MS = 1000L;
+  private static final long FOCUS_TIME_MS = 750L;
 
   private AdvancedMultimediaManager() {
     // do nothing

javame/src/com/google/zxing/client/j2me/LCDUIImageMonochromeBitmapSource.java

@@ -117,19 +117,27 @@ public final class LCDUIImageMonochromeBitmapSource implements MonochromeBitmapS
   }
 
   /**
-   * Extracts luminance from a pixel from this source. By default, the source is assumed to use RGB,
+   * An optimized approximation of a more proper conversion from RGB to luminance which
-   * so this implementation computes luminance is a function of a red, green and blue components as
+   * only uses shifts. See BufferedImageMonochromeBitmapSource for an original version.
-   * follows:
-   *
-   * <code>Y = 0.299R + 0.587G + 0.114B</code>
-   *
-   * where R, G, and B are values in [0,1].
    */
   private static int computeRGBLuminance(int pixel) {
-    // Coefficients add up to 1024 to make the divide into a fast shift
+    // Instead of multiplying by 306, 601, 117, we multiply by 256, 512, 256, so that
-    return (306 * ((pixel >> 16) & 0xFF) +
+    // the multiplies can be implemented as shifts.
-        601 * ((pixel >> 8) & 0xFF) +
+    //
-        117 * (pixel & 0xFF)) >> 10;
+    // Really, it's:
+    //
+    // return ((((pixel >> 16) & 0xFF) << 8) +
+    //         (((pixel >>  8) & 0xFF) << 9) +
+    //         (( pixel        & 0xFF) << 8)) >> 10;
+    //
+    // That is, we're replacing the coefficients in the original with powers of two,
+    // which can be implemented as shifts, even though changing the coefficients slightly
+    // corrupts the conversion. Not significant for our purposes.
+    //
+    // But we can get even cleverer and eliminate a few shifts:
+    return (((pixel & 0x00FF0000) >> 8)  +
+            ((pixel & 0x0000FF00) << 1) +
+            ((pixel & 0x000000FF) << 8)) >> 10;
   }
 
 }

javame/src/com/google/zxing/client/j2me/SnapshotThread.java

@@ -28,56 +28,64 @@ import javax.microedition.media.Player;
 import javax.microedition.media.control.VideoControl;
 
 /**
+ * Thread which does the work of capturing a frame and decoding it.
+ *
  * @author Sean Owen (srowen@google.com)
  */
 final class SnapshotThread extends Thread {
 
-  private static SnapshotThread currentThread;
-
   private final ZXingMIDlet zXingMIDlet;
+  private final Object waitLock;
+  private boolean done;
 
-  private SnapshotThread(ZXingMIDlet zXingMIDlet) {
+  SnapshotThread(ZXingMIDlet zXingMIDlet) {
     this.zXingMIDlet = zXingMIDlet;
+    waitLock = new Object();
+    done = false;
   }
 
-  static synchronized void startThread(ZXingMIDlet zXingMIDlet) {
+  void continueRun() {
-    if (currentThread == null) {
+    synchronized (waitLock) {
-      currentThread = new SnapshotThread(zXingMIDlet);
+      waitLock.notifyAll();
-      currentThread.start();
     }
   }
 
+  private void waitForSignal() {
+    synchronized (waitLock) {
+      try {
+        waitLock.wait();
+      } catch (InterruptedException ie) {
+        // continue
+      }
+    }
+  }
+
+  void stop() {
+    done = true;
+    continueRun();
+  }
+
   public void run() {
     Player player = zXingMIDlet.getPlayer();
-    try {
+    do {
-      AdvancedMultimediaManager.setFocus(player);
+      waitForSignal();
       try {
-        player.stop();
+        AdvancedMultimediaManager.setFocus(player);
+        byte[] snapshot = takeSnapshot();
+        Image capturedImage = Image.createImage(snapshot, 0, snapshot.length);
+        MonochromeBitmapSource source = new LCDUIImageMonochromeBitmapSource(capturedImage);
+        Reader reader = new MultiFormatReader();
+        Result result = reader.decode(source);
+        zXingMIDlet.handleDecodedText(result.getText());
+      } catch (ReaderException re) {
+        // Show a friendlier message on a mere failure to read the barcode
+        zXingMIDlet.showError("Sorry, no barcode was found.");
       } catch (MediaException me) {
-        // continue
+        zXingMIDlet.showError(me);
+      } catch (RuntimeException re) {
+        zXingMIDlet.showError(re);
       }
-      byte[] snapshot = takeSnapshot();
+    } while (!done);
-      Image capturedImage = Image.createImage(snapshot, 0, snapshot.length);
-      MonochromeBitmapSource source = new LCDUIImageMonochromeBitmapSource(capturedImage);
-      Reader reader = new MultiFormatReader();
-      Result result = reader.decode(source);
-      zXingMIDlet.handleDecodedText(result.getText());
-    } catch (ReaderException re) {
-      // Show a friendlier message on a mere failure to read the barcode
-      zXingMIDlet.showError("Sorry, no barcode was found.");
-    } catch (MediaException me) {
-      zXingMIDlet.showError(me);
-    } catch (RuntimeException re) {
-      zXingMIDlet.showError(re);
-    } finally {
-      try {
-        player.start();
-      } catch (MediaException me) {
-        // continue
-      }
-      currentThread = null;
-    }
-
   }
 
   private byte[] takeSnapshot() throws MediaException {

javame/src/com/google/zxing/client/j2me/VideoCanvas.java

@@ -23,6 +23,9 @@ import javax.microedition.lcdui.Displayable;
 import javax.microedition.lcdui.Graphics;
 
 /**
+ * The main {@link Canvas} onto which the camera's field of view is painted.
+ * This class manages decoding via {@link SnapshotThread}.
+ *
  * @author Sean Owen (srowen@google.com)
  */
 final class VideoCanvas extends Canvas implements CommandListener {
@@ -30,11 +33,14 @@ final class VideoCanvas extends Canvas implements CommandListener {
   private static final Command exit = new Command("Exit", Command.EXIT, 1);
 
   private final ZXingMIDlet zXingMIDlet;
+  private final SnapshotThread snapshotThread;
 
   VideoCanvas(ZXingMIDlet zXingMIDlet) {
     this.zXingMIDlet = zXingMIDlet;
     addCommand(exit);
     setCommandListener(this);
+    snapshotThread = new SnapshotThread(zXingMIDlet);
+    snapshotThread.start();
   }
 
   protected void paint(Graphics graphics) {
@@ -44,12 +50,16 @@ final class VideoCanvas extends Canvas implements CommandListener {
   protected void keyPressed(int keyCode) {
     // Any valid game key will trigger a capture
     if (getGameAction(keyCode) != 0) {
-      SnapshotThread.startThread(zXingMIDlet);
+      snapshotThread.continueRun();
+    } else {
+      super.keyPressed(keyCode);
     }
   }
 
   public void commandAction(Command command, Displayable displayable) {
-    if (command.getCommandType() == Command.EXIT || command.getCommandType() == Command.STOP) {
+    int type = command.getCommandType();
+    if (type == Command.EXIT || type == Command.STOP || type == Command.BACK || type == Command.CANCEL) {
+      snapshotThread.stop();
       zXingMIDlet.stop();
     }
   }