Java: User Interface Components and 2D Graphics

• A good GUI API or package would allow you to …
  • Create user interface components
  • Customize the behavior of the components
  • group and arrange the controls on the screen
  • access window manager facilities (e.g., reading image files, printing, and identifying which window is focused)
• User interface (WIMP - “Window, Icon, Menu, Pointing device”):
  • Window
  • Buttons
  • Menus
  • Text boxes
  • Dialog boxes
• Event handling:
  • Mouse
  • Keyboard
  • Focus / window
• These are the essentials of writing graphics-based applications

• Abstract Window Toolkit (AWT) - Native “peer” code; operating system dependent
  • Not all platforms support the same widget set (some are richer than others)
  • Also, different bugs in the AWT user interface library exist on different platforms
  • Widgets may have different behaviors on different platforms
• Swing - Consistent user experience across platforms; less dependent on underlying platform, as compared to AWT
• Many Swing components (classes) extend AWT components (classes).
  • Thus, both the AWT and Swing libraries are necessary (in most cases).
• Container - A user interface component that can contain other user interface components such as buttons and text fields
• Events
• Toolkit - Class that gets system-dependent information (e.g., getting the screen size)

• The top level window (that is, a window that is not contained inside another window)
• JFrame class of the Swing library
• JFrame extends the Frame class of the AWT library
• JFrame is a container
• Pertinent methods:
  • setSize()
  • setLocation()
  • setTitle()
  • setIconImage()
  • setVisible()

• JPanel class of the Swing library
• Provides the internal structure of a JFrame
• Is itself a container
• Has a surface onto which you can draw via paint() or paintComponent() methods
• Some Java game developers use Canvas (AWT) instead of JPanel (Swing)
  • The difference: a JPanel can contain other components while a Canvas cannot
  • paint() is used for Canvas.
  • paint() can also be used in JPanel.

• JButton
• JTextField
• JLabel
• JCheckBox
• JRadioButton
• JComboBox
• JMenuBar
• JPasswordField

• Event source (the widgets): button, text box, radio button, etc.
  • In response to mouse movement/click, keyboard press, etc.
• Event listener - An object to which a component has delegated the task of handling a particular kind of event
• The event source sends out event objects to all registered listeners when that event occurs.
• The listener objects will then use the information in the event object to determine their reaction to the event.

• MouseListener interface
• Uses MouseEvent class
• Required methods:
  • public void mouseClicked(MouseEvent e)
  • public void mousePressed(MouseEvent e)
  • public void mouseReleased(MouseEvent e)
  • public void mouseEntered(MouseEvent e)
  • public void mouseExited(MouseEvent e)

• Require FocusListener, KeyListener interfaces
• Uses KeyEvent class
• Required methods:
  • public void keyPressed (KeyEvent e)
  • public void keyTyped (KeyEvent e)
  • public void keyReleased (KeyEvent e)
  • public void focusGained (FocusEvent e)
  • public void focusLost (FocusEvent e)

• Vector:
  • Drawings defined as lines; no curves and limited colors
  • Benefits: No jagged lines (aliasing); only store endpoints of lines
  • Examples: Asteroids, Lunar Lander and Battlezone

• Raster:
  • Screen is made up of pixels
  • Colors are defined by mixtures of 3 color sources: red, green, and blue (RGB)
  • Benefits: Can easily draw solid surfaces; cheaper
  • Drawbacks: More memory-intensive (but memory is cheap); aliasing problems

• Point
• Line
• Polygon
  • Closed (all lines connected)
  • Defined by a list of vertices

• Two coordinate spaces in Java
  • User space - Where the graphics primitives are defined; device independent
  • Device space - The coordinate system of an output device, such as a screen, window, or a printer; device dependent
  • The necessary conversions between user space and device space are performed automatically during rendering

• Links:
  • http://java.sun.com/docs/books/tutorial/2d/index.html
  • http://courses.coreservlets.com/Course-Materials/java5.html (follow “Desktop Graphics in Java” link)
  • Uses older Graphics class but still useful:
    • http://www.csse.monash.edu.au/~cema/courses/CSE5910/lectureFiles/lecture7b.htm
• The Graphics class
  • Introduced in JDK version 1.0
  • Methods to draw lines and basic shapes
  • Very limited drawing options (e.g., cannot vary the line thickness; cannot rotate shapes)
• The Graphics2D class
  • Allows newer type of Graphics object: Graphics2D extends Graphics
  • More sophisticated control over geometry, coordinate transformations, color management, and text layout
  • Supports shape manipulations
• Packages (Java 2D API)
  • java.awt.*
    • The main package for the Java Abstract Window Toolkit.
  • java.awt.geom.*
    • The Java standard library of two dimensional geometric shapes such as lines, ellipses, and quadrilaterals.
  • java.awt.font.*
    • The library for manipulating glyphs in Java.
  • java.awt.color.*
    • The library dealing with the many different ways that color can be represented.
  • java.awt.image.*
    • The library for manipulating graphical images.

      public void paintComponent (Graphics g)
      {
        Graphics2D g2 = (Graphics2D)g;
        // This is where you will do your work
        ...
        ...
      }

• drawLine(int x1, int y1, int x2, int y2)
• drawRect(int x, int y, int width, int height)
• fillRect(int x, int y, int width, int height)
• drawOval(int x, int y, int width, int height)
• fillOval(int x, int y, int width, int height)
• drawString(String str, int x, int y)
• drawPolygon(int[] xPoints, int[] yPoints, int nPoints)
• fillPolygon(int[] xPoints, int[] yPoints, int nPoints)
• For more, see http://java.sun.com/javase/6/docs/api/java/awt/Graphics.html

• Use setColor() or setPaint()
• A number of standard colors in Java:
  • Color.white
  • Color.red
  • Color.blue
  • Color.cyan
  • Color.green
• Or, specify your own color using RGB values
  • Color(int r, int g, int b)
  • Color(float r, float g, float b)

• Geometric shapes are organized in an object-oriented fashion
  • Line2D
  • Rectangle2D
  • Ellipse2D
  • The three classes above implement the Shape interface
• To draw a shape, create an object of a class that implements the Shape interface and then call the draw() or fill() method of the Graphics2D class.
• setStroke() - Set the line width.
  • Need to create a stroke via BasicStroke()
• Rectangle2D.Double(double x, double y, double w, double h)
• Rectangle2D.Float(float x, float y, float w, float h)
• Ellipse2D.Double(double x, double y, double w, double h)
• Ellipse2D.Float(float x, float y, float w, float h)
• Point2D.Double(double x, double y)
• Line2D.Double(Point2D start, Point2D end)
• Line2D.Double(double startX, double startY, double endX, double endY)
• Arc2D.Double(double x, double y, double w, double h, double start, double extent, int type)
• Arc2D.Float(float x, float y, float w, float h, float start, float extent, int type)
• RoundRectangle2D.Double(double x, double y, double w, double h, double arcw, double arch)
• RoundRectangle2D.Float(float x, float y, float w, float h, float arcw, float arch)

• translate() - Specify a translation offset in the x and y directions
• rotate() - Specify an angle of rotation in radians
• shear() - Specify a shearing factor in the x and y directions

• scale() - Specify a scaling factor in the x and y directions

• Whether it's this:
  • 
• … or this:
  • →
• After you've done your painting through paint() or paintComponent()
  • Repaint:
    • repaint() - Force repainting on the screen.
      • repaint() causes paintComponent() to be called for all components.

• Need, at the very least, java.awt.image.* (Image class (AWT))
• drawImage(Image img, int x, int y, ImageObserver observer)

• Draw a red line (add code to draw more shapes at different locations)

• Drag a red line to paint a region

• Load and draw an external image file

• Use keyboard events to move a string around