CSC223, Class 27: Swing (3): Graphics (Briefly)

Admin:
* Late: Louisa
* Missing: Kat, Evan, Omondi, Luis
* Exam now due Monday.
* Questions on the exam?  Bring them Friday!
* Is the PolySci event still going on? 

Overview:
* Basics
* Typical steps
* Examples

/Graphics Basics/

* Graphics in a user interface are hard (or at least have a lot of complicating issues)
  * How do you know when to draw?  
    * When an event happens in the window (e.g., user types or clicks)
    * When something embedded within the window changes (e.g., image in a Web page)
    * When the window is changed (e.g., resized, expanded from compressed version)
    * When another window moves over it
    * When program code indicates it is necessary (e.g., animation)
    * ...
  * How do you handle all these different possibilities?
    * Redraw every N units of time: Inefficient
    * Hope that the "world" tells you when its time to redraw (Swing provides this)
  * What do you redraw? Only the portion of interest
    * Smart systems tell you what the "portion of interest" is
    * Smart systems ignore drawing commands outside the "portion of interest"
  * How do you deal with nested or overlapping objects?
    * You want your windowing toolkit to deal with this, too
* In AWT, components override the
  paint(java.awt.Graphics) 
  method
  * Problem: Expected programmer to deal with nesting
* In Swing, components override the
  paintComponent(java.awt.Grapics)
  method
  * The paint method in JComponent does the smart thing
* Painting model:
  * The point (0,0) is upper-left
  * Increasing x goes to the right
  * Increasing y goes down

/How do you write a paintComponent() method?/

	public void paintComponent(Graphics brush)
	{
* Step one (usually): Figure out the bounds of this component
  java.awt.Rectangle bounds = this.getBounds()
  int x = bounds.getX();
  int y = bounds.getY();
  int w = bounds.getWidth();
  int h = bounds.getHeight();
  * Alternate
    int x = this.getX();
    int y = this.getY();
    int w = this.getWidth();
    int h = this.getHeight();
* Step two (sometimes, for efficiency), Figure out the "clip region" (the portion that is being drawn)
 		Rectangle bounds = brush.getClipBounds()
* Repeat the following steps as often as necessary
	* Step threea: Choose a color to draw with
		brush.setColor(java.awt.Color)
	* Step threeb: Draw something
		brush.fillRect(...)
		brush.fillOval(...)
		...
* Sometimes: Call the method in the superclass
	super.paintComponent()  (first, last, middle, never)

/Example/

* Warning!  Currently doesn't work right.