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UID – Swing and Graphics Chris Coleman

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1 UID – Swing and Graphics Chris Coleman (

2 Today Graphics When / Why ? Painting What can be done Java 2D Full Screen API

3 Graphics – A big topic Could run a whole lecture course on how to use the various graphics capabilities that Swings APIs provide. Use the Tutorials and API docs at:

4 When do I need to use graphics? (1) Avoid using graphics if possible You may well only need icons labels and buttons borders styled text areas JEditorPane JTextPane

5 When do I need to use graphics? (2) May need graphics if Wish to drastically change appearance of an existing component Draw shapes to screen Draw text to screen Animation Invent / customise your own component

6 Painting (1) Component painting repaint() automatically called when necessary. Eg Window unhidden revalidate() automatically called before repaint when needed. Eg when component sizes or position have changed Threads and painting painting on the event-dispatching thread repaint() and revalidate() are thread safe

7 Painting (2) Double buffering Painting performed to off screen buffer, then flushed to screen when finished. Opaque components Improves performance. Time not spent painting behind components. Shape of painting areas always rectangular non-opaque (transparent) components can appear any shape, although need to use glass panes to mask hit detection area

8 Painting order Visibility based on containment hierarchy Background (if opaque) Custom painting Border Child components repaints if transparent component repaints, all components under it must also repaint. This is costly, therefore use opaque when possible

9 What graphics tools are available in Swing? Java AWT Graphics Basic but usually enough Shapes Text Images Java 2D graphics Extends the AWT graphics to provide much more, eg gradients, textures etc

10 Custom painting (1) Occurs between background and border Extend component and customise JPanel recommended e.g. class myPaintingPanel extends JPanel { can also use atomic components e.g. class myPaintingButton extends JButton { Code goes in overridden paintComponent() method public void paintComponent(Graphics g) {

11 Custom painting (2) When writing custom painting code should not reproduce painting functionality of any other Swing component Before doing anything else in paintComponent() invoke super.paintComponent() or setOpaque(false)

12 Painting coordinates Component sizes in pixels (0,0) at top left corner (width-1,height-1) at bottom right corner Border sizes (e.g. a 1-pixel border) (1,1) at top left (width-2, height-2) at bottom right General painting area for b pixel border [ {b,b} : {w-(b+1), h-(b+1)} ]

13 Getting painting coordinates Use component getWidth() and getHeight() Get border sizes with getInsets() e.g. to get width and height of custom painting area use something like: Insets insets = getInsets(); int currentWidth = getWidth() - insets.left - insets.right; int currentHeight = getHeight() - - insets.bottom;

14 Repainting custom paints Calling repaint() method requests a repaint to occur repaint() paints whole component & any others that need it if transparent repaint(int leftx,int lefty,int width,int height); only repaints a specified area Component painted after all pending events dispatched. Painting should be kept short - Done in event thread - slows GUI

15 Graphics - shapes and text (1) Properties stored in Graphics object. Represents state eg Color, Font, etc Methods of Graphics can draw... Shapes lines, rectangles, 3D rectangles, round-edged rectangles, ovals, arcs, polygons Text Draw string to screen as a graphic

16 Graphics - shapes and text (2) Drawing a shape on screen Use paintComponent Graphics void paintComponent(Graphics g) { super(g) g.setColor(Color.RED); g.drawRect(x, y, width, height); } shapes: x and y specify upper left

17 Graphics - shapes and text (3) Drawing a string on screen Use paintComponent Graphics again void paintComponent(Graphics g) { super(g) g.setFont(new Font(Serif, Font.PLAIN, 12)); g.drawSring(Java Swing, x, y); } x and y specify baseline left of text

18 Graphics - Images Swing Icons by far and away the easiest method of displaying graphics. If more features needed then use the AWT/Graphics functionality Supports GIF, PNG and JPEG NOT BMP Loading and displaying images Image myImage = Toolkit.getDefaultToolkit().getImage(filename); g.drawImage(myImage, x, y, this); g.drawImage(myImage, x, y, width, height,this);

19 Tracking Images MediaTracker class utility class used to track the status of a number of images for a particular component. Can get information about any errors and associated images ImageObserver interface implemented by all components can use to get notifications about loading progress of image as its constructed.

20 Java2D API (Graphics2D) Provides enhanced image, graphics and text capabilities Done through extensions to AWT Graphics API Amongst others provides Hit detection on Shapes text and images Complex Printing Support Texture rendering Complex Shapes/lines

21 Java2D Shapes Rectangle Shapes QuadCurve2D and CubicCurve2D GeneralPath Arbitrary shapes made by connecting lines

22 Java 2D - Text Often easier to use JLabels since much of the work is done for you Use the drawString method Eg g.drawString(Hello, x, y); To set font use setFont method Create an instance of Font

23 Java 2D - Images Much more powerful than basic image display Images are best rendered in a Buffer off screen as a BufferedImage Then drawn to screen with call to Graphics2D.drawImage Graphics2D provides variety of image filtering options sharpen/blur, rotate, transform, scale etc

24 Java 2D – (VERY) Basic use Simply cast the Graphics object to Graphics2D void paintComponent(Graphics g) { super(g); Graphics g2 = (Graphics2D)g.create(); g2.setColor(Color.BLACK); g2.drawRect(x, y, width, height); g2.dispose(); }

25 The Full Screen API Full Name: Full Screen Exclusive API Introduced in JDK 1.4 Allows programmer to suspend windowing system and draw directly to the screen Good for games, slide shows and dedicated terminal applications Not covered here, but excellent tutorial found here:

26 Coursework (1) Tips… Remember to relate features you design back to the users you defined. Any design of application is ok SO LONG AS ITS REASONABLY JUSTIFIED WITH REFERENCE TO YOUR USERS AND DESIGN PRINCIPLES Grab images off web to increase niceness of your application

27 Coursework (2) Finally, if the Swing is a struggle – remember that time spent adding little bits of functionality could also be spent writing the report which is still worth 40% of the total. Its a UID course – NOT a Swing Showcase…

28 Coursework (3) Not allowed to use JBuilder – sorry… Must code all Swing yourself Deadline 3:30pm Thursday 15th November Plagiarism – (Cheating) and a reminder not to All code is checked against all others, the web and the past couple of years submissions by a very clever computer…

29 Coursework (3) Support Email Will answer as much as I can, Try to provide as much info as possible about the problem. Labs Mondays 2-5 A05 Example Code available at:

30 Summary Swing +ves Swings good because its Platform Independent Swing makes it easy to construct simple GUIs quickly Swing –ves Swing is not always as Platform Independent as it claims Can get confusing when GUIs get BIG, but aided by using an IDE Java - its not the fastest language ever...

31 The End.

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