Add a main() method for convenient debugging

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

README.md

@@ -22,5 +22,10 @@ directory, run _Help>Refresh Menus_ and the plugin will be available in
 _Process>Process Pixels_ (this can be changed by editing
 _src/main/resources/plugins.config_).
 
+Developing plugins in an IDE is convenient, especially for debugging. To
+that end, the plugin contains a _main()_ method which sets the _plugins.dir_
+system property (so that the plugin is added to the Plugins menu), starts
+ImageJ, loads an image and runs the plugin.
+
 Since this project is intended as a starting point for your own
 developments, it is in the public domain.

src/main/java/Process_Pixels.java

 import ij.IJ;
+import ij.ImageJ;
 import ij.ImagePlus;
 import ij.gui.GenericDialog;
 import ij.plugin.filter.PlugInFilter;
@@ -154,4 +155,30 @@ public class Process_Pixels implements PlugInFilter {
 			"a template for processing each pixel of an image"
 		);
 	}
+
+	/**
+	 * Main method for debugging.
+	 *
+	 * For debugging, it is convenient to have a method that starts ImageJ, loads an
+	 * image and calls the plugin, e.g. after setting breakpoints.
+	 *
+	 * @param args unused
+	 */
+	public static void main(String[] args) {
+		// set the plugins.dir property to make the plugin appear in the Plugins menu
+		Class<?> clazz = Process_Pixels.class;
+		String url = clazz.getResource("/" + clazz.getName().replace('.', '/') + ".class").toString();
+		String pluginsDir = url.substring(5, url.length() - clazz.getName().length() - 6);
+		System.setProperty("plugins.dir", pluginsDir);
+
+		// start ImageJ
+		new ImageJ();
+
+		// open the Clown sample
+		ImagePlus image = IJ.openImage("http://imagej.net/images/clown.jpg");
+		image.show();
+
+		// run the plugin
+		IJ.runPlugIn(clazz.getName(), "");
+	}
 }