fix various issues in TreeViewer

1) Issue: The tree "jumps" from a larger scale to a much smaller scale when starting dragging the scale slider.

Cause: Initially the slider was not correctly positioned. It always assumed a scale of 1. 

Solution: I now calculate the initial slider position using the current scale (was 1.5).

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2) Issue: NullPointerException when the scale slider is dragged to the very left.

Cause: The formula "v / 1000.0 + 1.0" results in a scale of 0.0 when using -1000 (left position). A scale of 0 is not supported.

Solution: in setScale I now check for "<= 0.0". In the case I use scale 1. In addition I changed the lower bound of the slider to -999, i.e. the left position represents the scale "0.001".

---

3) Issue: when scaling the scrollbars are not added/updated/removed

Cause: when scaling the preferred size of the TreeViewer must be updated as the ScrollPane refers to the preferredSize for scrolling.

Solution: now calling "updatePreferredSize" in setScale. This will set the preferred size to the "scaled tree size". It also ensures parents will be notified and the view is repainted.

---

4) Issue: only an upper left part of the tree is painted.

Cause: the TreeViewer overwrote the getWidth/Height and returned unchanged values (800x600). Only this area in painted. If the preferred size exceeded this size the remaining area was not painted.

Solution: Removed the overwrite of getWidth/Height. As one consequence the dialog will start at maximum size for large tree layouts.

[git-p4: depot-paths = "//depot/code/antlr4/main/": change = 9481]

runtime/Java/src/org/antlr/v4/runtime/tree/gui/TreeViewer.java

@@ -102,9 +102,6 @@ public class TreeViewer extends JComponent {
 	protected int nodeHeightPadding = 0; // added above/below
 	protected int arcSize = 0;           // make an arc in node outline?
 
-	protected int width = 800;
-	protected int height = 600;
-
 	protected double scale = 1.0;
 
 	protected Color boxColor = null;     // set to a color to make it draw background
@@ -125,11 +122,19 @@ public class TreeViewer extends JComponent {
 								 new DefaultConfiguration<Tree>(gapBetweenLevels,
 																gapBetweenNodes),
                                  useIdentity);
-		Dimension size = treeLayout.getBounds().getBounds().getSize();
-		setPreferredSize(size);
+		updatePreferredSize();
 		setFont(font);
 	}
 
+	private void updatePreferredSize() {
+		setPreferredSize(getScaledTreeSize());
+		invalidate();
+		if (getParent() != null) {
+			getParent().validate();
+		}
+		repaint();
+	}
+
 	// ---------------- PAINT -----------------------------------------------
 
 	protected void paintEdges(Graphics g, Tree parent) {
@@ -237,8 +242,7 @@ public class TreeViewer extends JComponent {
 
 		// Wrap viewer in scroll pane
 		JScrollPane scrollPane = new JScrollPane(viewer);
-		// Make it tree size up to width/height of viewer
-		viewer.setPreferredSizeToScaledTree();
+		// Make the scrollpane (containing the viewer) the center component
 		contentPane.add(scrollPane, BorderLayout.CENTER);
 
 	  	// Add button to bottom
@@ -259,8 +263,9 @@ public class TreeViewer extends JComponent {
 		bottomPanel.add(wrapper, BorderLayout.SOUTH);
 
 		// Add scale slider
+		int sliderValue = (int) ((viewer.getScale()-1.0) * 1000);
 		final JSlider scaleSlider = new JSlider(JSlider.HORIZONTAL,
-										  -1000,1000,0);
+										  -999,1000,sliderValue);
 		scaleSlider.addChangeListener(
 			new ChangeListener() {
 				@Override
@@ -278,18 +283,12 @@ public class TreeViewer extends JComponent {
 		dialog.setVisible(true);
 	}
 
-	protected void setPreferredSizeToScaledTree() {
+	private Dimension getScaledTreeSize() {
 		Dimension scaledTreeSize =
 			treeLayout.getBounds().getBounds().getSize();
 		scaledTreeSize = new Dimension((int)(scaledTreeSize.width*scale),
 									   (int)(scaledTreeSize.height*scale));
-		if ( scaledTreeSize.width < width ) {
-			setWidth(scaledTreeSize.width);
-		}
-		if ( scaledTreeSize.height < height ) {
-			setHeight(scaledTreeSize.height);
-		}
-		setPreferredSize(new Dimension(width, height));
+		return scaledTreeSize;
 	}
 
 	public void open() {
@@ -435,25 +434,10 @@ public class TreeViewer extends JComponent {
 	}
 
 	public void setScale(double scale) {
+		if(scale <= 0) {
+			scale = 1;
+		}
 		this.scale = scale;
-		repaint();
-	}
-
-	@Override
-	public int getHeight() {
-		return height;
-	}
-
-	public void setHeight(int height) {
-		this.height = height;
-	}
-
-	@Override
-	public int getWidth() {
-		return width;
-	}
-
-	public void setWidth(int width) {
-		this.width = width;
+		updatePreferredSize();
 	}
 }