Swing Hacks

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Chapter 8, Rendering

#56 Create a Magnifying Glass Component

HACK

Build the Magnifying Glass

The DetachedMagnifyingGlass will need to keep track of the Component it’s

viewing, the current mouse location in that component, a zoom factor, and

its own size. It will also need an instance of the AWT

Robot

for taking screen

grabs. The other thing it needs to do is to have a

MouseMotionListener

, so

that it will get updates on the cursor’s position and, when it changes, do a

new grab and

repaint( )

.

The

DetachedMagnifyingGlass code is shown in Example 8-1.

Example 8-1. JComponent to provide a magnified view of another JComponent

public class DetachedMagnifyingGlass extends JComponent

implements MouseMotionListener {

double zoom;

JComponent comp;

Point point;

Dimension mySize;

Robot robot;

public DetachedMagnifyingGlass (JComponent comp,

Dimension size,

double zoom) {

this.comp = comp;

// flag to say don't draw until we get a MouseMotionEvent

point = new Point (-1, -1);

comp.addMouseMotionListener(this);

this.mySize = size;

this.zoom = zoom;

// if we can't get a robot, then we just never

// paint anything

try {

robot = new Robot( );

} catch (AWTException awte) {

System.err.println ("Can't get a Robot");

awte.printStackTrace( );

}

}

public void paint (Graphics g) {

if ((robot == null) || (point.x == -1))

{

g.setColor (Color.blue);

g.fillRect (0, 0, mySize.width, mySize.height);

return;

}

Rectangle grabRect ...