Drags within the image
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/*
* SelectionDemo.java is a 1.4 application that requires one other file:
* images/starfield.gif
*/
import javax.swing.BoxLayout;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.event.MouseInputAdapter;
import java.awt.*;
import java.awt.event.MouseEvent;
/*
* This displays an image. When the user drags within the image, this program
* displays a rectangle and a string indicating the bounds of the rectangle.
*/
public class SelectionDemo {
JLabel label;
static String starFile = "starfield.gif";
private void buildUI(Container container, ImageIcon image) {
container.setLayout(new BoxLayout(container, BoxLayout.PAGE_AXIS));
SelectionArea area = new SelectionArea(image, this);
container.add(area);
label = new JLabel("Drag within the image.");
label.setLabelFor(area);
container.add(label);
//Align the left edges of the components.
area.setAlignmentX(Component.LEFT_ALIGNMENT);
label.setAlignmentX(Component.LEFT_ALIGNMENT); //redundant
}
public void updateLabel(Rectangle rect) {
int width = rect.width;
int height = rect.height;
//Make the coordinates look OK if a dimension is 0.
if (width == 0) {
width = 1;
}
if (height == 0) {
height = 1;
}
label.setText("Rectangle goes from (" + rect.x + ", " + rect.y
+ ") to (" + (rect.x + width - 1) + ", "
+ (rect.y + height - 1) + ").");
}
/** Returns an ImageIcon, or null if the path was invalid. */
protected static ImageIcon createImageIcon(String path) {
java.net.URL imgURL = SelectionDemo.class.getResource(path);
if (imgURL != null) {
return new ImageIcon(imgURL);
} else {
System.err.println("Couldn't find file: " + path);
return null;
}
}
/**
* Create the GUI and show it. For thread safety, this method should be
* invoked from the event-dispatching thread.
*/
private static void createAndShowGUI() {
//Make sure we have nice window decorations.
JFrame.setDefaultLookAndFeelDecorated(true);
//Create and set up the window.
JFrame frame = new JFrame("SelectionDemo");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//Set up the content pane.
SelectionDemo controller = new SelectionDemo();
controller.buildUI(frame.getContentPane(), createImageIcon(starFile));
//Display the window.
frame.pack();
frame.setVisible(true);
}
public static void main(String[] args) {
//Schedule a job for the event-dispatching thread:
//creating and showing this application's GUI.
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGUI();
}
});
}
private class SelectionArea extends JLabel {
Rectangle currentRect = null;
Rectangle rectToDraw = null;
Rectangle previousRectDrawn = new Rectangle();
SelectionDemo controller;
public SelectionArea(ImageIcon image, SelectionDemo controller) {
super(image); //This component displays an image.
this.controller = controller;
setOpaque(true);
setMinimumSize(new Dimension(10, 10)); //don't hog space
MyListener myListener = new MyListener();
addMouseListener(myListener);
addMouseMotionListener(myListener);
}
private class MyListener extends MouseInputAdapter {
public void mousePressed(MouseEvent e) {
int x = e.getX();
int y = e.getY();
currentRect = new Rectangle(x, y, 0, 0);
updateDrawableRect(getWidth(), getHeight());
repaint();
}
public void mouseDragged(MouseEvent e) {
updateSize(e);
}
public void mouseReleased(MouseEvent e) {
updateSize(e);
}
/*
* Update the size of the current rectangle and call repaint.
* Because currentRect always has the same origin, translate it if
* the width or height is negative.
*
* For efficiency (though that isn't an issue for this program),
* specify the painting region using arguments to the repaint()
* call.
*
*/
void updateSize(MouseEvent e) {
int x = e.getX();
int y = e.getY();
currentRect.setSize(x - currentRect.x, y - currentRect.y);
updateDrawableRect(getWidth(), getHeight());
Rectangle totalRepaint = rectToDraw.union(previousRectDrawn);
repaint(totalRepaint.x, totalRepaint.y, totalRepaint.width,
totalRepaint.height);
}
}
protected void paintComponent(Graphics g) {
super.paintComponent(g); //paints the background and image
//If currentRect exists, paint a box on top.
if (currentRect != null) {
//Draw a rectangle on top of the image.
g.setXORMode(Color.white); //Color of line varies
//depending on image colors
g.drawRect(rectToDraw.x, rectToDraw.y, rectToDraw.width - 1,
rectToDraw.height - 1);
controller.updateLabel(rectToDraw);
}
}
private void updateDrawableRect(int compWidth, int compHeight) {
int x = currentRect.x;
int y = currentRect.y;
int width = currentRect.width;
int height = currentRect.height;
//Make the width and height positive, if necessary.
if (width < 0) {
width = 0 - width;
x = x - width + 1;
if (x < 0) {
width += x;
x = 0;
}
}
if (height < 0) {
height = 0 - height;
y = y - height + 1;
if (y < 0) {
height += y;
y = 0;
}
}
//The rectangle shouldn't extend past the drawing area.
if ((x + width) > compWidth) {
width = compWidth - x;
}
if ((y + height) > compHeight) {
height = compHeight - y;
}
//Update rectToDraw after saving old value.
if (rectToDraw != null) {
previousRectDrawn.setBounds(rectToDraw.x, rectToDraw.y,
rectToDraw.width, rectToDraw.height);
rectToDraw.setBounds(x, y, width, height);
} else {
rectToDraw = new Rectangle(x, y, width, height);
}
}
}
}
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