1. 2D Graphics in Java COMP53 Nov 14, 2007

2. Applets and Applications Java applications are stand-alone programs – start execution with main() – runs in JVM directly under the OS Java applets are browser programs – start in class derived from JApplet – event driven – runs in JVM within the browser

3. Basic Applet // Java core packages import java.awt.*; // Java extension packages import javax.swing.*; public class BlankGraphicsApplet extends JApplet { public void paint(Graphics g) { // call superclass's paint method (paints background) super.paint(g); // Here's where we'd put // application specific drawing instructions }

4. Embedding Applet in Web Page

5. Basic Graphics Application import java.awt.*; import java.awt.event.*; import javax.swing.*; public class BlankGraphicsFrame extends JFrame { public BlankGraphicsFrame() { super("Blank Graphics Frame"); setSize(600, 400); show(); } public void paint(Graphics g) { super.paint(g); // Here's where we'd put application specific drawing instructions } public static void main(String args[]) { BlankGraphicsFrame application = new BlankGraphicsFrame(); application.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE ); }

6. When to paint()? System calls paint, usually for one of the following reasons: – The component is first made visible on the screen. – The component is resized. – The component has damage that needs to be repaired. For example, a covering window has been moved. The application calls paint, because its internal state has changed. – a button press triggers change in graphics – animated objects move or change

7. Basics of Drawing Drawing commands are methods of the Graphics object passed to paint() Coordinates are from top left of window x increase to right y increase downward

8. Selecting a Drawing Color predefined color: – g.setColor(Color.red) – orange, pink, cyan, magenta, yellow, black, white, gray, lightGray, darkGray, red, green, blue RGB defined color: – g.setColor(new Color(200,20,250)) – red, green and blue in range 0 to 255 RGB defined color: – g.setColor(new Color(0.7,0.1,0.8)) – red, green and blue in range 0.0 to 1.0

9. Basic Shapes rectangles and ovals – (x1,y1) is upper left corner of shape – g.drawRect(x1,y1,width,height) rectangle outline – g.fillRect(x1,y1,width, height) solid rectangle – g.drawOval(x1,y1,width,height) oval outline – g.fillOval(x1,y1,width, height) solid oval – g.drawLine(x1,y1,x2,y2) line from (x1, y1) to (x2,y2)

10. Text select font: g.setFont(new Font(“Arial”, Font.BOLD, 12)) font name, font attributes, font size draw text: g.drawString(“Print This!”, 20, 40) string to draw, (x1,y1) top left postion