Graphics in Swing. Engineering 5895 Faculty of Engineering & Applied Science Memorial University of Newfoundland

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Nickolas Jefferson
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1 Graphics in Swing Engineering 5895 Faculty of Engineering & Applied Science Memorial University of Newfoundland 1

2 paintcomponent and repaint Each Swing component has the following paint methods: void paintcomponent( Graphics g ) void repaint() paintcomponent( Graphics g ) Override when extending JComponent to change the visual presentation of the component Called when part or all of the screen devoted to a Component needs redrawing. Should generally call super.paintcomponent(g) as your first action repaint() Schedules a later call to paint your component; May combine calls repaint(x, y, width, height) For efficiency, marks only the specified rectangular region as requiring painting 2 / 15

3 Painting in Swing In JComponent, the paint( Graphics g ) method follows (roughly) the following algorithm: public void paint( Graphics g ) { paintcomponent( g ); paintborder( g ); paintchildren( g ); } The children appear to be in front of their parent Do not override or call paint directly Override paintcomponent and call repaint The Graphics object will come already configured: Foreground and background colour, font, and other attributes are set to those of the JComponent 3 / 15

4 Example from Java Tutorials: SwingPaintDemo3 4 / 15

5 The Graphics class Provides a uniform interface to multiple raster devices Typically we just use the Graphics object passed to paintcomponent Note that paintcomponet is thus polymorphic it operates on any underlying object that extends Graphics We can also create Graphics objects To the screen / the printer / images in memory This is an example of the Adapter pattern! Component.getGraphics() Image.getGraphics() PrintJob.getGraphics() g.create() // A clone of graphics object g. g.create( x, y, w, h ) // a translated clone. Always call Graphics.dispose() on any Graphics object you create! 5 / 15

6 Graphics Graphics objects provide two kinds of methods Methods that access/mutate the state of the Graphics object: setcolor( Color ) setclip( Shape ) setfont( Font ) setpaintmode() / setxormode() hitclip( x, y, w, h ) Methods that affect the underlying raster: drawrect( x, y, w, h ) / fillrect( x, y, w, h ) drawoval( x, y, w, h ) / filloval( x, y, w, h ) drawline( x0, y0, x1, y1 ) drawstring( x, y, string ) drawimage( image, x, y, observer ) 6 / 15

7 Example: ClipDemo 7 / 15

8 Coordinate systems All coordinates are in terms of pixels and are ints. (x,y) is the point between four pixels: (x-1,y-1), (x-1,y), (x,y-1), (x,y) We can obtain the width and height of the component by Component.getWidth() and Component.getHeight() (0,0) is the top left of corner (getwidth(), 0) is the top right corner (0, getheight()) is the lower left corner 8 / 15

9 Screen Coordinates 0 The effect of g.fillrect( 0, 0, 3, 4) and 2 g.drawrect(3, 1, 3, 4) / 15

10 Text To paint text on the screen: g.setfont( font ) ; g.drawstring( x, y, string ) ; (x,y) is the leftmost point of the string s baseline i.e. descenders will go below the line y. The rest of each letter is above. The font is an object of class Font e.g. new Font(Font.SANS_SERIF, Font.PLAIN, 10 ) ; Possible font names: {Font.DIALOG, Font.DIALOG_INPUT, Font.MONOSPACED, Font.SERIF, Font.SANS_SERIF} Possible font styles: {Font.PLAIN, Font.ITALIC, Font.BOLD, Font.ITALIC Font.BOLD} 10 / 15

11 Font Metrics Given a string we may want to know how much space it will take. For this we use a FontMetrics object Height FontMetrics fm = g.getfontmetrics(font) ; int h = fm.getheight() ; // Standard height int w = fm.stringwidth(message) ; Happy Birthday Descent Leading Ascent 11 / 15

12 Graphics2D Graphics2D extends Graphics and adds new capabilities As long as your runtime environment (JRE) is at least version 1.2, the Graphics object passed to paint (because of a call to repaint()) can be trusted to actually be an instance of protected void paintcomponent( Graphics g ) { super.paintcomponent( g ); assert g instanceof Graphics2D, Graphics2D is required by +this.getclass(); Graphics2D g2d = (Graphics2D) g; and from here on we use g2d instead of g } 12 / 15

13 Graphics2D Graphics2D objects work in terms of floating point not integers Affine transformations are supported: Translation, rotation, scaling, shearing Graphics2D objects can draw a variety of Shape objects: Shape shape; g2d.draw( shape ); g2d.fill( shape ); 13 / 15

14 Shapes Shape is an interface with lots of implementations Point2D Point2D Shape l Shape r p0 = new Point2D.Double(x, y); p1 = new Point2D.Double(x+w, y+h) ; = new Line2D.Double( p0, p1 ) ; = new Rectangle2D.Double( x, y, w, h) ; Shape e = new Ellipse2D.Double( x, y, w, h) ; 14 / 15

15 Examples: TransformDemo1 TransformDemo2 RobotDemo 15 / 15

Java How to Program, 9/e. Copyright by Pearson Education, Inc. All Rights Reserved.

Java How to Program, 9/e. Copyright by Pearson Education, Inc. All Rights Reserved. Java How to Program, 9/e Copyright 1992-2012 by Pearson Education, Inc. All Rights Reserved. Overview capabilities for drawing two-dimensional shapes, controlling colors and controlling fonts. One of