CSC 308 – Graphics Programming

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

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.php3?bid=19

Features • Main window • Graphics canvas • Some lines drawn

Let’s Say “Hi!”

Java’s 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.

Gapp and Gcanvas are ours – we’re 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 isn’t 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

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

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.WindowAdapter() { public void windowClosing(java.awt.event.WindowEvent e) { thisWindowClosing(e); } }); }//end - initComponents

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); }

Upon Closer Examination… you may be asking, this program doesn’t actually seem to call the paintComponent method and where does it get “g” the Graphics object from? You are right, it doesn’t. paintComponent is what is known as a “callback” method. It’s 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 don’t have to worry about it.

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, it’s easiest to create a grid, label it, and plot your points.

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. Let’s take a look at their description…

Java Graphics Class API • http://java.sun.com/j2se/1.5.0/docs/api/

Homework: Due Wednesday, 8/30/06 • Modify the Gcanvas.java code to draw a square. • Create from this a “Swirling Square” as seen below.

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)+(u*Qx) and P1y = ((1-u)*Py)+(u*Qy) and so on and so on…

CSC 308 – Graphics Programming