Swing Hacks

Translucent Drag-and-Drop #69

Chapter 9, Drag-and-Drop

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353

HACK

solution is simply to display a translucent copy of the component itself,

referred to as a ghost in the code. Figure 9-10 shows a ghost in mid-drag.

This time, you will not use the package

java.awt.dnd; you’ll need your own

framework for this level of sophistication. By breaking out of the pre-built

box, you gain full control of drag-and-drop.

Drawing a Ghost

The very first thing you need is a glass pane able to draw a translucent pic-

ture over the UI. A glass pane is nothing more than a transparent

JPanel.

The code of

GhostGlassPane is very simple, as shown in Example 9-7.

Figure 9-10. A ghost is a translucent copy of a Swing component

Example 9-7. Creating a glass pane for ghosting

import java.awt.*;

import java.awt.image.*;

import javax.swing.*;

public class GhostGlassPane extends JPanel

{

private AlphaComposite composite;

private BufferedImage dragged = null;

private Point location = new Point(0, 0);

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Chapter 9, Drag-and-Drop

#69 Translucent Drag-and-Drop

HACK

This glass pane has two properties: the picture to be displayed and its loca-

tion. To make the picture translucent, use an

AlphaComposite instance.

Besides colors, strokes, and painters, Java2D drawings can be affected by

composites that define how the newly drawn pixels are mixed ...