Created a scrollable panel that scrolls entire components into view for

unit scrolling. (Is only smart about vertical scrolling, horizontal
scrolling moves in fixed increments.)


git-svn-id: https://samskivert.googlecode.com/svn/trunk@609 6335cc39-0255-0410-8fd6-9bcaacd3b74c

projects/samskivert/src/java/com/samskivert/swing/ScrollablePanel.java

@@ -0,0 +1,127 @@
+//
+// $Id: ScrollablePanel.java,v 1.1 2002/02/28 16:24:03 mdb Exp $
+
+package com.samskivert.swing;
+
+import java.awt.Component;
+import java.awt.Dimension;
+import java.awt.Insets;
+import java.awt.LayoutManager;
+import java.awt.Rectangle;
+
+import javax.swing.JPanel;
+import javax.swing.Scrollable;
+import javax.swing.SwingConstants;
+
+/**
+ * A {@link JPanel} extension that implements the {@link Scrollable}
+ * interface, instructing it to scroll partially obscured components into
+ * view if scrolling is done in the direction of a partially obscured
+ * component. If no component is partially obscured, the next component is
+ * scrolled into view in its entirety. Presently the code only works with
+ * vertically laid out components, horizontal scrolling simply moves by a
+ * default number of pixels every time.
+ */
+public class ScrollablePanel extends JPanel
+    implements Scrollable
+{
+    /**
+     * Pass through constructor.
+     */
+    public ScrollablePanel (LayoutManager layout, boolean isDoubleBuffered)
+    {
+        super(layout, isDoubleBuffered);
+    }
+
+    /**
+     * Pass through constructor.
+     */
+    public ScrollablePanel (LayoutManager layout)
+    {
+        super(layout);
+    }
+
+    /**
+     * Pass through constructor.
+     */
+    public ScrollablePanel (boolean isDoubleBuffered)
+    {
+        super(isDoubleBuffered);
+    }
+
+    // documentation inherited from interface
+    public Dimension getPreferredScrollableViewportSize ()
+    {
+        return getPreferredSize();
+    }
+
+    // documentation inherited from interface
+    public int getScrollableUnitIncrement (
+        Rectangle visibleRect, int orientation, int direction)
+    {
+        Insets insets = getInsets();
+
+        if (orientation == SwingConstants.HORIZONTAL) {
+            // nothing sensible to do here
+
+        } else {
+            if (direction > 0) {
+                int rectbot = visibleRect.y + visibleRect.height;
+                Component comp = getComponentAt(insets.left, rectbot);
+
+                // if there's no component at the edge, drop down 5
+                // pixels and look again
+                if (comp == this) {
+                    comp = getComponentAt(insets.left, rectbot+5);
+                }
+
+                if (comp != this && comp != null) {
+                    int compbot = comp.getY() + comp.getHeight();
+                    return compbot - rectbot + 5;
+                }
+
+            } else {
+                Component comp = getComponentAt(insets.left, visibleRect.y);
+
+                // if there's no component at the edge, move up 5
+                // pixels and look again
+                if (comp == this) {
+                    comp = getComponentAt(insets.left, visibleRect.y-5);
+                }
+
+                if (comp != this && comp != null) {
+                    return visibleRect.y - comp.getY() + 5;
+                }
+            }
+        }
+
+        return DEFAULT_SCROLL_AMOUNT;
+    }
+
+    // documentation inherited from interface
+    public int getScrollableBlockIncrement (
+        Rectangle visibleRect, int orientation, int direction)
+    {
+        if (orientation == SwingConstants.HORIZONTAL) {
+            return visibleRect.width;
+        } else {
+            return visibleRect.height;
+        }
+    }
+
+    // documentation inherited from interface
+    public boolean getScrollableTracksViewportWidth ()
+    {
+        return false;
+    }
+
+    // documentation inherited from interface
+    public boolean getScrollableTracksViewportHeight ()
+    {
+        return false;
+    }
+
+    /** The number of pixels to scroll if we can't find a component to
+     * scroll into view or if we're scrolling horizontally. */
+    protected static final int DEFAULT_SCROLL_AMOUNT = 10;
+}