CSC 308 Graphics Programming

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CSC 308 Graphics Programming

• Say Hi to Graphics
• i.e. A first, simple graphics program

Dr. Paige H. Meeker Computer Science Presbyterian
College, Clinton, SC
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Lecture 2

• Creating Simple Graphics in Java
• Homework
• Material modified from Computer Graphics via
  Java by Ian Ferguson online ebook and a nice
  download) http//www.ablibris.com/site/review.php
  3?bid19

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Features

• Main window
• Graphics canvas
• Some lines drawn

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Lets Say Hi!
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Javas Machinery

• In order to draw things on screen (which is what
  this is all about) you have to have quite a bit
  of Java machinery in place before you can start.

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Gapp and Gcanvas are ours were developing
them. JFrame and JPanel from which they inherit,
are part of the Java Foundation Classes - in
particular they are part of the swing GUI
components. The class Gapp inherits from
JFrame, so when a Gapp object is created, a new
GUI window appears on the screen. A
Gcanvas/JPanel is simply something we can draw
on, but it isnt allowed to be on screen by
itself, it must be part of a JFrame. So what we
actually need is an instance of Gapp with an
instance of Gcanvas inside it
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Gapp main()

• static public void main(String args)
• // Main entry point
• try
• Gapp myGapp new Gapp()
• myGapp.initComponents()
• myGapp.setVisible(true)
• catch (Exception e)
• e.printStackTrace()
• //end main

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Gapp initComponents()

• public void initComponents() throws Exception
• setLocation(new java.awt.Point(0, 30))
• setSize(new java.awt.Dimension(350, 400))
• setTitle("Graphics Application")
• getContentPane().add(new Gcanvas())
• addWindowListener(new java.awt.event.WindowAdapte
  r()
• public void windowClosing(java.awt.event.WindowE
  vent e)
• thisWindowClosing(e)
• )
• //end - initComponents

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• public void paintComponent(Graphics g)
• g.drawLine(100,50,100,150)
  g.drawLine(100,100,150,100)
  g.drawLine(150,100,150,150)
  g.drawLine(200,150,200,100)
  g.drawLine(200,50,200,60)

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Upon Closer Examination

• you may be asking, this program doesnt actually
  seem to call the paintComponent method and where
  does it get g the Graphics object from? You are
  right, it doesnt. paintComponent is what is
  known as a callback method. Its actually
  called by the system everytime the JPanel object
  it belongs to needs to be displayed on screen and
  likewise the system passes us the mysterious g
  to provide all of those useful functions - we
  dont have to worry about it.

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So,

• Our program hi is actually a simple drawing of
  5 lines, each with its own start and end point.
  To draw using this technique, its easiest to
  create a grid, label it, and plot your points.

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Graphics Primitives

• A graphics primitive can be loosely defined as a
  drawing function which the system makes available
  to the applications programmer.
• Java implements a comprehensive set of graphics
  primitives. Lets take a look at their
  description

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Java Graphics Class API

• http//java.sun.com/j2se/1.5.0/docs/api/

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Homework Due Wednesday, 8/30/06

• Modify the Gcanvas.java code to draw a square.
• Create from this a Swirling Square as seen
  below.

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Homework Hint

• This basically draws a square, then a second
  square inside the first reduced in size by 0.1
  and slightly rotated. This continues for 40
  iterations.
• HINT P1x ((1-u)Px)(uQx) and P1y
  ((1-u)Py)(uQy) and so on and so on