nb- The first thing to note, this is done using Java 7, creating a transparent window in Java 6 is done differently and is not possible below update 10 (I think)
Basically, this creates a transparent window, size and location to cover the entire virtual screen (that is, if you have multiple screens, it will cover everything).
Then I use JPanel as the main container for capturing mouse events and performing paint effects.
The panel is made transparent. This allows you to always be below the panel (and frame) to remain visible. Then I painted it in a transparent color (I did this to emphasize the fact).
When you click and drag an area, it is displayed.
import java.awt.BorderLayout; import java.awt.Color; import java.awt.EventQueue; import java.awt.Graphics; import java.awt.Graphics2D; import java.awt.GraphicsDevice; import java.awt.GraphicsEnvironment; import java.awt.Point; import java.awt.Rectangle; import java.awt.event.MouseAdapter; import java.awt.event.MouseEvent; import java.awt.geom.Area; import javax.swing.JFrame; import javax.swing.JPanel; import javax.swing.SwingUtilities; import javax.swing.UIManager; import javax.swing.UnsupportedLookAndFeelException; public class MySnipTool { public static void main(String[] args) { new MySnipTool(); } public MySnipTool() { EventQueue.invokeLater(new Runnable() { @Override public void run() { try { UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName()); } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) { } JFrame frame = new JFrame("Testing"); frame.setUndecorated(true); frame.setBackground(new Color(0, 0, 0, 0)); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setLayout(new BorderLayout()); frame.add(new CapturePane()); Rectangle bounds = getVirtualBounds(); frame.setLocation(bounds.getLocation()); frame.setSize(bounds.getSize()); frame.setAlwaysOnTop(true); frame.setVisible(true); } }); } public class CapturePane extends JPanel { private Rectangle selectionBounds; private Point clickPoint; public CapturePane() { setOpaque(false); MouseAdapter mouseHandler = new MouseAdapter() { @Override public void mouseClicked(MouseEvent e) { if (SwingUtilities.isLeftMouseButton(e) && e.getClickCount() == 2) { System.exit(0); } } @Override public void mousePressed(MouseEvent e) { clickPoint = e.getPoint(); selectionBounds = null; } @Override public void mouseReleased(MouseEvent e) { clickPoint = null; } @Override public void mouseDragged(MouseEvent e) { Point dragPoint = e.getPoint(); int x = Math.min(clickPoint.x, dragPoint.x); int y = Math.min(clickPoint.y, dragPoint.y); int width = Math.max(clickPoint.x - dragPoint.x, dragPoint.x - clickPoint.x); int height = Math.max(clickPoint.y - dragPoint.y, dragPoint.y - clickPoint.y); selectionBounds = new Rectangle(x, y, width, height); repaint(); } }; addMouseListener(mouseHandler); addMouseMotionListener(mouseHandler); } @Override protected void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2d = (Graphics2D) g.create(); g2d.setColor(new Color(255, 255, 255, 128)); Area fill = new Area(new Rectangle(new Point(0, 0), getSize())); if (selectionBounds != null) { fill.subtract(new Area(selectionBounds)); } g2d.fill(fill); if (selectionBounds != null) { g2d.setColor(Color.BLACK); g2d.draw(selectionBounds); } g2d.dispose(); } } public static Rectangle getVirtualBounds() { Rectangle bounds = new Rectangle(0, 0, 0, 0); GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment(); GraphicsDevice lstGDs[] = ge.getScreenDevices(); for (GraphicsDevice gd : lstGDs) { bounds.add(gd.getDefaultConfiguration().getBounds()); } return bounds; } }
Equally, you can simply create a transparent frame that the user can change. You will be responsible for implementing the entire change code yourself, but the solution will still be viable.
Update
You may also need to check if the OS / hardware supports transparency ...
GraphicsConfiguration config = GraphicsEnvironment.getLocalGraphicsEnvironment().getDefaultScreenDevice().getDefaultConfiguration(); if (!AWTUtilities.isTranslucencyCapable(config)) { System.out.println("Transluceny is not supported"); } if (!AWTUtilities.isTranslucencySupported(AWTUtilities.Translucency.PERPIXEL_TRANSPARENT)) { System.out.println("PerPeixel Transparency is not supported"); }
Updated with an alternative approach
This is an alternative approach to the problem. Basically, it takes a screenshot and displays it in a window. This allows us to control the selection / selection as needed.
The disadvantage of this is that it is a static result, you will not get any current animation effects.
import java.awt.AWTException; import java.awt.BorderLayout; import java.awt.Color; import java.awt.Dimension; import java.awt.EventQueue; import java.awt.Graphics; import java.awt.Graphics2D; import java.awt.GraphicsDevice; import java.awt.GraphicsEnvironment; import java.awt.HeadlessException; import java.awt.Point; import java.awt.Rectangle; import java.awt.Robot; import java.awt.event.MouseAdapter; import java.awt.event.MouseEvent; import java.awt.image.BufferedImage; import javax.swing.JFrame; import javax.swing.JPanel; import javax.swing.UIManager; import javax.swing.UnsupportedLookAndFeelException; public class SnipWithScreenShoot { public static void main(String[] args) { new SnipWithScreenShoot(); } public SnipWithScreenShoot() { EventQueue.invokeLater(new Runnable() { @Override public void run() { try { UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName()); } catch (ClassNotFoundException ex) { } catch (InstantiationException ex) { } catch (IllegalAccessException ex) { } catch (UnsupportedLookAndFeelException ex) { } try { JFrame frame = new JFrame("Test"); frame.setUndecorated(true); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setLayout(new BorderLayout()); frame.add(new TestPane()); frame.pack(); frame.setLocationRelativeTo(null); frame.setVisible(true); } catch (AWTException exp) { exp.printStackTrace(); System.out.println("That sucks"); } } }); } public class TestPane extends JPanel { private BufferedImage image; private Rectangle selection; public TestPane() throws AWTException { Robot bot = new Robot(); image = bot.createScreenCapture(getVirtualBounds()); MouseAdapter handler = new MouseAdapter() { @Override public void mousePressed(MouseEvent e) { selection = new Rectangle(e.getPoint()); repaint(); } @Override public void mouseDragged(MouseEvent e) { Point p = e.getPoint(); int width = Math.max(selection.x - e.getX(), e.getX() - selection.x); int height = Math.max(selection.y - e.getY(), e.getY() - selection.y); selection.setSize(width, height); repaint(); } }; addMouseListener(handler); addMouseMotionListener(handler); } @Override public Dimension getPreferredSize() { return image == null ? super.getPreferredSize() : new Dimension(image.getWidth(), image.getHeight()); } @Override protected void paintComponent(Graphics g) { super.paintComponent(g); if (image != null) { Graphics2D g2d = (Graphics2D) g.create(); g2d.drawImage(image, WIDTH, 0, this); if (selection != null) { g2d.setColor(new Color(225, 225, 255, 128)); g2d.fill(selection); g2d.setColor(Color.GRAY); g2d.draw(selection); } g2d.dispose(); } } } public static Rectangle getVirtualBounds() { Rectangle bounds = new Rectangle(0, 0, 0, 0); GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment(); GraphicsDevice lstGDs[] = ge.getScreenDevices(); for (GraphicsDevice gd : lstGDs) { bounds.add(gd.getDefaultConfiguration().getBounds()); } return bounds; } }