1. Java Graphics

2. Review 3 kinds of elements in components API? Layout managers Events Extend vs. Implement

3. Useful Java DataStructures Vector (dynamic array) V = new Vector( ); V.add(item); V.elementAt(5); HashTable (maps keys to items) H = new HashTable( ); H.add(key, item); H.get(key); Iterators (automatic FOR loops) I = V.iterator( ); While (I.hasNext( )) dosomething(I.next( ));

4. Graphics Window is like a painter’s canvas App must paint its window contents Java components paint themselves Anything else: Programmer When to paint? How to paint? JButton

5. How to Paint?

6. Pixels

7. Coordinate System Upside-down Cartesian Y window = height - Y cartesian (0,0) (width,0) (0,height)(width, height)

8. Component Hierarchy Each component has its own subwindow Subwindow = rectangular area within parent component Has own coordinate system Clipping: Can’t paint outside its subwindow Can’t paint over child components? (0,0) (w p, h p ) (0,0) (w b, h b ) JPanel JButton

9. Painting Components Can paint any component JPanel is good for custom graphics area JButton JPanel

10. Painting in Java import java.awt.Graphics import java.awt.Graphics2D// Java2 1. Get the “graphics context” of component Graphics g = myJPanel.getGraphics( ); Graphics2D g2 = (Graphics2D) g; 2. Paint in it g2.drawLine(x1,y1, x2,y2);

11. Graphics Primitives DrawFill Point (x,y) Line (pt1,pt2) PolyLine (pt list) Arc Oval (pt, w,h) Rectangle (pt, w,h) RoundRectangle Polygon (pt list) Image (file, x,y) Text (string, x,y) label

12. Graphics Attributes Color Font Stroke attributes: –Line width, dash, end caps, joins, miter Paint attributes: –Color, gradient, texture Composite: –Blending Transforms: –Translate, rotate, flip, shear, scale

13. Color Combinations of Red, Green, Blue Each [0, 255] Java: new Color(255, 150, 0) Hokie Orange

14. in Java Drawing primitives: g2.drawLine( ),.drawRect( ), … g2.fillRect( ), … Object oriented: 1.Create shape: import java.awt.geom.* shape = new Point2D.Float(x, y); Line2D, Rect2D, CubicCurve2D, … 2.Draw the shape: g2.draw(shape); g2.fill(shape);

15. in Java Color and font: g2.setColor( new Color(r,g,b) ); g2.setFont( new Font(…) ); Advanced: g2.setStroke(…); g2.setPaint(…); g2.setComposite(…); g2.setTransform(…); 1.Set graphics attributes 2.Draw graphics

16. When to Paint?

17. Re-Paint Screen is like a painter’s canvas All windows paint on the same surface! Windows don’t “remember” whats under them Need to re-paint when portions are newly exposed Receive Repaint events Open, resize, bring to front When other windows in front move, resize, close

18. MyApp

19. Open WinExp, Notepad

20. Close WinExplorer Repaint event sent to: MyApp, Desktop

21. Desktop gets repaint event

22. MyApp gets repaint event MyApp JPanel gets repaint event

23. MyApp gets repaint event MyApp JPanel forwards repaint event to JButton

24. Repainting Static Graphics Repaint event: Erase subwindow (fill with background color) Draw subwindow contents

25. In Java Repaint event: Java Swing components catch repaint event, and call their paintComponent( ) method Default paintComponent( ) method paints component –E.g. panel background color Sub-class the component (typically JPanel) Over-ride paintComponent( ) method Custom graphics here Can call repaint( ) to invoke paintComponent( )

26. Code public class MyPanel extends JPanel { public void paintComponent(Graphics g){ super.paintComponent(g); // erases background Graphics2D g2 = (Graphics2D)g; //cast for java2 // my graphics: g2.setColor(new Color(255,0,0)); g2.fillRect(10,10,200,50); g2.setColor(new Color(0,0,0)); g2.drawString("Hello World", 10, 10); } Hello World

27. Typical program structure for Dynamic Graphics Store data structure of window contents E.g. user drawn picture in paint program Repaint event: Erase window (draw background color) Draw window contents using data structure Other event that alters window contents: modify the data structure send repaint event

28. In JBuilder Subclassing JPanel Overriding paintComponent( ) Using subclassed JPanel in a JFrame

29. Storing window contents 2 approaches: Store logical contents in a data structure »E.g. drawing program: lines, shapes, colors, … » Store visual contents as an off-screen image (bitmap) »E.g. pixels »Then use g2.drawImage( ) in paintComponent( ) »

30. Problem: Flashing Ugly flashing when repaint: Paint background Redraw shapes

31. Solution: Double buffering

32. Double buffered repaint: Draw all graphics in temporary off-screen image »Paint background color »Paint shapes Then paint image to JPanel Bonus: Swing does this for you! Draw graphics on JPanel JPanel maintains off-screen image

33. What Subwindows Do Directs mouse input to correct component Determines repaint events Own coordinate system Don’t need repaint when moving Clipping: hides drawing behind a subwindow Some subwindows remember what’s under them: Popup menus