Graphics and Java 2D

public void paint(Graphics g)

• The paint() method we've used in applets actually comes from class Component
• The paint() method for any component is called when that component needs to be drawn
• Drawing a component is typically an event-driven process (when a program starts, when another window covers then uncovers, etc). So the programmer seldom calls paint() itself
• The programmer can call repaint() (also a Component method) to force the paint operation
• method paint() takes as a parameter a reference variable of type Graphics -- which is an abstract class. The object will be a subtype that handles the drawing context for the given platform

class Graphics and other useful helper classes

• Graphics - helps manage drawing on the screen for GUI applications and applets.
  • Keeps track of state information like current font, current color, the Component object being drawn on, and more
  • Has methods for drawing various kinds of shapes (lines, ovals, polygons, rectangles, etc) as well as strings.
  • Also has methods for setting the font, the color, the current clipping area, the paint mode, and other status information
  
  
• Color - used for specifying colors in components and drawings
  • colors stored and specified with RGB (Red Green Blue) values
  • RGB values can be specified with ints (0-255) or floats (0.0-1.0)
  • Color constants exist for common colors (Color.BLUE, Color.GREEN, etc)
  • To set or find out the current drawing color, use the Graphics methods getColor() and setColor(). Example:

      g.setColor(Color.MAGENTA);
      g.setColor(new Color(255, 128, 3));	// using RGB values 

  • JColorChooser - a javax.swing component that enables application users to choose colors
  
  
• Font - specify fonts used in Graphics drawings
  • Physical fonts are actual fonts on a system -- these depend on platform and what fonts are installed on a system
  • Logical fonts are the 5 font families supported in Java: Serif, Sans Serif, Monospaced, Dialog, and DialogInput. When using logical fonts, an appropriate font on the given system will be chosen
  • Font constructor takes three parameters: font name, font style, font size
    • Font name can be physical or logical
    • Font styles are plain, italics, or bold
    • Font size measured in points
  • To set or find out the current drawing font, use the Graphics methods getFont() and setFont(). Example:

      Font f = g.getFont();			// retrieve current font
      g.setFont(new Font("Serif", Font.ITALICS, 12)); 

  • Other methods available in class Font to set or retrieve properties for a Font object
  
  
• FontMetrics - abstract class. Encapsulates information and properties about the rendering of a font on screen
  • Helps track more specific font information like height, descent, ascent, and leading (interline spacing)
  • Graphics class has a couple of methods named getFontMetrics():

       FontMetrics m1, m2;
       m1 = g.getFontMetrics();	// retrieve info about current drawing font 
       m2 = g.getFontMetrics(f1);	// retrieve info about font f1
     

• Polygon - helper class for representing information about Polygons
  • Stores a list of (x,y) coordinate pairs, representing vertices of a polygon
  • Several Graphics class methods are for drawing polygons - drawPolygon(), drawPolyLine, fillPolygon. There are versions of these last two that take a Polygon object as a parameter.
  
   

Java2D

Java 2D API -- for an overview, see this page on the Java web site.

A Java-2D Tutorial

• Allows more complex drawing, like lines of varying thickness, filling shapes with colors and patterns, drawing dashed lines, composite overlapping text and graphics, gradients and textures, and more
• Involves a variety of packages:
  • java.awt
  • java.awt.image
  • java.awt.color
  • java.awt.font
  • java.awt.geom
  • java.awt.print
  • java.awt.image.renderable
• Need to use an instance of class Graphics2D, which is a subclass of class Graphics. Must cast the Graphics object in the paint() method into a Graphics2D reference when using:

    Graphics2D g2d = (Graphics2D) g;
  

Deitel examples - Chapter 12