super("SpringLayout Compass Demo");
setSize(500,300);
setDefaultCloseOperation(EXIT_ON_CLOSE);
SpringLayout sl = new SpringLayout();
Container c = getContentPane();
c.setLayout(sl);
int offset = 50; // gap between buttons and outside edge
int w = 80; // width of buttons
int h = 26; // height of buttons
int border = 3; // border around viewport
Spring offsetS = Spring.constant(offset);
Spring borderS = Spring.constant(border);
Spring widthS = Spring.constant(w);
Spring halfWidthS = FractionSpring.half(widthS);
Spring heightS = Spring.constant(h);
Spring halfHeightS = FractionSpring.half(heightS);
Spring leftEdgeS = sl.getConstraint(SpringLayout.WEST, c);
Spring topEdgeS = sl.getConstraint(SpringLayout.NORTH, c);
Spring rightEdgeS = sl.getConstraint(SpringLayout.EAST, c);
Spring bottomEdgeS = sl.getConstraint(SpringLayout.SOUTH, c);
Spring xCenterS = FractionSpring.half(rightEdgeS);
Spring yCenterS = FractionSpring.half(bottomEdgeS);
Spring leftBorder = Spring.sum(leftEdgeS, borderS);
Spring topBorder = Spring.sum(topEdgeS, borderS);
Spring northX = Spring.sum(xCenterS, Spring.minus(halfWidthS));
Spring southY = Spring.sum(bottomEdgeS, Spring.minus(Spring.sum(heightS,
offsetS)));
Spring eastX = Spring.sum(rightEdgeS, Spring.minus(Spring.sum(widthS,
offsetS)));
Spring eastY = Spring.sum(yCenterS, Spring.minus(halfHeightS));
c.add(nb, new SpringLayout.Constraints(northX, offsetS, widthS, heightS));
c.add(sb, new SpringLayout.Constraints(northX, southY, widthS, heightS));
c.add(wb);
sl.getConstraints(wb).setX(offsetS);
sl.getConstraints(wb).setY(eastY);
sl.getConstraints(wb).setWidth(widthS);
sl.getConstraints(wb).setHeight(heightS);
c.add(eb);
sl.getConstraints(eb).setX(eastX);
sl.getConstraints(eb).setY(eastY);
sl.getConstraints(eb).setWidth(widthS);
sl.getConstraints(eb).setHeight(heightS);
c.add(viewport); // this sets a bounds of (0,0,pref_width,pref_height)
// The order here is important...need to have a valid width and height
// in place before binding the (x,y) location
sl.putConstraint(SpringLayout.SOUTH, viewport, Spring.minus(borderS),
SpringLayout.SOUTH, c);
sl.putConstraint(SpringLayout.EAST, viewport, Spring.minus(borderS),
SpringLayout.EAST, c);
sl.putConstraint(SpringLayout.NORTH, viewport, topBorder,
SpringLayout.NORTH, c);
sl.putConstraint(SpringLayout.WEST, viewport, leftBorder,
SpringLayout.WEST, c);
ImageIcon icon = new ImageIcon(getClass().getResource(terrain));
viewport.setView(new JLabel(icon));
// Hook up the buttons. See the CompassScroller class (on-line) for details
// on controlling the viewport.
nb.setActionCommand(CompassScroller.NORTH);
sb.setActionCommand(CompassScroller.SOUTH);
wb.setActionCommand(CompassScroller.WEST);
eb.setActionCommand(CompassScroller.EAST);
CompassScroller scroller = new CompassScroller(viewport);
nb.addActionListener(scroller);
sb.addActionListener(scroller);
eb.addActionListener(scroller);
wb.addActionListener(scroller);
setVisible(true);
