ttools: partially address issues with swing plot2task animation

Swing animation is not parallelised.  This meant that for slow plots,
most frames are never seen with swing animations from Plot2Tasks.
Fix this by replacing SwingUtilities.invokeLater with invokeAndWait.
However the real fix would be to parallelise the plotting.
It wouldn't be too hard, but I'm not doing it now.
Add comments to the source code to describe what would have to be
done.

ttools/src/main/uk/ac/starlink/ttools/plot2/task/AbstractPlot2Task.java

@@ -5,6 +5,7 @@
 import java.awt.Insets;
 import java.awt.Rectangle;
 import java.io.IOException;
+import java.lang.reflect.InvocationTargetException;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
@@ -541,6 +542,19 @@ private void animateSwing( Environment baseEnv, PlotContext context,
         RowSequence aseq = animateTable.getRowSequence();
         final JComponent holder = new JPanel( new BorderLayout() );
         DataStore dataStore = null;
+
+        /* The swing animation is not parallelised, but should be.
+         * It's like this.  The work is not (mostly) done by creating the
+         * PlotDisplay component plot component, it's done when that
+         * component paints itself, i.e. on the event dispatch thread,
+         * so I can't easily do parallel plotting and feed the results
+         * to the EDT to display.
+         * To parallelise it, I should cause that painting work to be
+         * done before the component is posted, and cached within the
+         * PlotDisplay object ready for fast plotting when it becomes visible.
+         * PlotDisplay is more or less set up to do this, but it would
+         * need to know its dimensions to know how to do the plot,
+         * which requires a bit of additional plumbing. */
         try {
             for ( long irow = 0; aseq.next(); irow++ ) {
                 Environment frameEnv =
@@ -551,18 +565,29 @@ private void animateSwing( Environment baseEnv, PlotContext context,
                 final JComponent panel =
                     executor.createPlotComponent( dataStore, true, true );
                 final boolean init = irow == 0;
-                SwingUtilities.invokeLater( new Runnable() {
-                    public void run() {
-                        holder.removeAll();
-                        holder.add( panel, BorderLayout.CENTER );
-                        holder.revalidate();
-                        holder.repaint();
-                        if ( init ) {
-                            painter.postComponent( holder );
-                        }                   
-                    }
-                } );
-            }   
+
+                /* It's necessary to use invokeAndWait here, since the
+                 * display painting is slow.  If invokeLater is used,
+                 * most frames are never seen.  If I fix it so that
+                 * most of the work is done outside the EDT,
+                 * I can change this back to invokeLater. */
+                try {
+                    SwingUtilities.invokeAndWait( new Runnable() {
+                        public void run() {
+                            holder.removeAll();
+                            holder.add( panel, BorderLayout.CENTER );
+                            holder.revalidate();
+                            holder.repaint();
+                            if ( init ) {
+                                painter.postComponent( holder );
+                            }                   
+                        }
+                    } );
+                }
+                catch( InvocationTargetException e ) {
+                    throw new TaskException( "Painting error: " + e, e );
+                }
+            }
         }
         finally {
             aseq.close();