![Color
• Combinations of Red, Green, Blue
• Each [0, 255]
• Java: new Color(255, 150, 0)
Hokie Orange](https://image.slidesharecdn.com/java4-graphics-221211043938-1ad936e4/85/Java4-Graphics-ppt-13-320.jpg)
Java4-Graphics.ppt
- 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
- 6. Pixels
- 7. Coordinate System • Upside-down Cartesian • Ywindow = height - Ycartesian (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) (wp, hp) (0,0) (wb, hb) JPanel JButton 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 Draw Fill • 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
- 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
- 32. Solution: Double buffering • 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