====== User Interface Components and 2D Graphics ======

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===== User Interface and Interactive Components =====

  * 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

===== The Java Approach =====

  * Abstract Window Toolkit (AWT) - Native "peer" code; operating system dependent
          * Not all platforms support the same widget set (some richer than others)
          * Different bugs in the AWT user interface library 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 extend AWT components.
    * 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 Frame ====

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

{{ http://www.javacoder.co.cc/wp-content/uploads/2009/07/upd1.png?200|JFrame-JPanel relationship}}

==== The Panel ====

    * JPanel
    * **The internal structure of a JFrame**
    * Is 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.

==== Swing User Interface Components ====

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

==== Event Handling ====

    * 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.

=== Handling Mouse Clicking Events ===

    * MouseListener class
    * MouseEvent
    * 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)

=== Handling Keyboard Events ===

    * Require FocusListener, KeyListener classes
    * KeyEvent
    * 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)

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===== 2D Graphics =====

==== Vector vs. Raster Graphics ====

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

==== 2D Rendering Primitives ====

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

==== Coordinate System ====

    * 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

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===== 2D Graphics in Java =====

    * Links:
      * http://java.sun.com/docs/books/tutorial/2d/index.html
      * http://courses.coreservlets.com/Course-Materials/java5.html (follow "Java 2D" link)
      * Uses older Graphics class but still useful:
        * http://www.csse.monash.edu.au/~cema/courses/CSE5910/lectureFiles/lecture7b.htm      
        * http://java.sun.com/products/jfc/tsc/articles/painting/
    * 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)
    * Graphics2D class
          * A new 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.
          * java.awt.print.*
            * The library of tools for writing to paper.


==== The Java 2D paintComponent() Method in a JPanel ====

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

==== Old Graphics Primitive Methods (That Still 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

==== Colors ====

    * 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)

{{ http://www.csse.monash.edu.au/~cema/courses/CSE5910/lectureFiles/images/lect8a/lect8aGraphicsClassHierarchy.png?250|Class Diagram for (some of) Java's graphics routines}}

==== Graphics2D Primitive Methods ====

    * 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)

==== Manipulations and Transformations ====

    * 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

==== Moving Pictures ====

    * Whether it's this:
      * {{http://rockhopper.monmouth.edu/~jchung/cs498gd/media/spaceinvaders.gif}}
    * ... or this:
      * {{http://rockhopper.monmouth.edu/~jchung/cs498gd/media/Minesweeper_0.gif}} -> {{http://rockhopper.monmouth.edu/~jchung/cs498gd/media/Minesweeper_flag.gif}}
    * 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.

==== Drawing Images (external images, e.g. gif, png, jpg) ====

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

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===== Code Samples =====

  * [[http://rockhopper.monmouth.edu/~jchung/cs498gd/labs/ui2d/drawLine.java|Draw a red line]]

  * [[http://rockhopper.monmouth.edu/~jchung/cs498gd/labs/ui2d/moveLine.java|Failed attempt to animate a line]]

  * [[http://rockhopper.monmouth.edu/~jchung/cs498gd/labs/ui2d/moveStringKb.java|Use keyboard events to move a string around]]

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===== Lab Activity - Etch-A-Sketch (tm) emulator? =====

  * Purpose: Utilize Java Swing, Graphics2D, and KeyListener to construct an Etch-A-Sketch (tm) emulator.

  * Introduction
    * You are to construct an electronic version of a [[http://www.dilbert.com/dyn/str_strip/000000000/00000000/0000000/000000/20000/0000/900/20939/20939.strip.gif|famous childhood toy]] that draws lineographic images.
    * Instead of using two knobs to control the drawing stylus, the arrow keys will be moved.

  * Instructions
    * In Eclipse, create a new Java project "Sketch"
    * Download the [[http://rockhopper.monmouth.edu/~jchung/cs498gd/labs/ui2d/moveStringKb.java|template Sketch.java]] into your project folder
          * The template is partially complete with the application window / frame and key listener implemented. The drawing function(s) are left out.

  * Additional
    * Make holding down the shift key produce a longer line.
    * Update the program so that a press of the spacebar will clear your sketch drawing.
    * Update the program so it will accept key combinations to draw diagonal lines.
      * For example: <up>+<right> draws a diagonal line up and to the right.
        * Of course, it would be simpler to just map a single key to draw a diagonal line, but many games use a combination of the arrow keys to produce certain actions, such as jumping across obstacles.

  * Links
    * http://java.sun.com/javase/6/docs/api/java/awt/Image.html (AWT Image Class)
    * http://java.sun.com/javase/6/docs/api/java/awt/event/InputEvent.html (handling keyboard modifiers, e.g. <shift>)
    * http://math.hws.edu/eck/cs124/javanotes3/c6/s5.html (something on Java VK_ keycodes)

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