Download presentation
Presentation is loading. Please wait.
Published byIreland Simer Modified over 9 years ago
1
1 Drawing C Sc 335 Object-Oriented Programming and Design Rick Mercer
2
2 Drawing Outline Drawing with a Graphics object Graphics and Graphics2D paintComponent and repaint draw and fill messages Strings, Lines, Rectangle, Ellipse, Polygons Colors Text and Fonts Drawing Images Toolkit to convert jpg and gif files into Images
3
3 Drawing Drawing with a Graphics Object The use of graphics is common among modern software systems Java has strong support for graphics coordinate system for Java graphics drawing shapes such as lines, ovals, rectangles,... basic animation techniques the use of color the use of fonts drawing images
4
4 Drawing The Coordinate System A simple two-dimensional coordinate system exists for each graphics context or drawing surface Each point on the coordinate system represents a single pixel top left corner of the area is coordinate // This string will be drawn 20 pixels right, // 40 pixels down as the lower left corner; // other shapes are upper right g2.drawString("is in Panel1", 20, 40); A drawing surface has a width and height Anything drawn outside of that area is not visible
5
5 Drawing The Coordinate System x y Y X
6
6 Drawing Draw on a JPanel Need to extend a class that extends JComponent JPanel is good To draw things: extend JPanel have the class override the paintComponent method panel surface is transparent, so send drawing messages inside paintComponent to the graphic context a Graphics2D object we'll reference with g2
7
7 Drawing Put something in a JPanel Implement a JPanel class and draw a few strings import java.awt.*; public class DrawingPanel extends javax.swing.JPanel { // Override the paintComponent method in JPanel @Override public void paintComponent(Graphics g) { super.paintComponent(g); // Always call this Graphics2D g2 = (Graphics2D) g; g2.drawString("Put this in g, which", 20, 20); g2.drawString("is in Panel", 20, 40); g2.drawString("which is in MyFrame", 20, 60); }
8
8 Drawing Then add the JPanel to a JFrame to see the drawing import javax.swing.JFrame; public class DrawOnAPanel extends JFrame { public static void main(String[] args) { new DrawOnAPanel().setVisible(true); } public DrawOnAPanel() { setTitle("A Frame with a panel"); setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); setSize(200, 120); add(new DrawingPanel()); }
9
9 Drawing The Graphics Object paintComponent 's Graphics g argument represents a "graphical context" object. You can tell it to draw things on the panel If you want another method to draw, pass the Graphics object to it—it like a canvas that understands draws The actual object passed to every JPanel is a Graphics2D, so you can cast to Graphics2D Never send paintcomponent messages send repaint() messages instead
10
10 Drawing The Graphics Context Graphics is still around, but Java added an improved 2D Library in Java 1.3, use Graphics2D Better drawing capabilities It is analogous to using swing ( JButton, JFrame ) rather than older awt components ( Button, Frame )
11
11 Drawing First cast Graphics to Graphics2D Send messages to g2 such as drawString draw fill setColor and setFont Rectangle2D body = // xcoord, ycoord, width, height new Rectangle2D.Double(30.0, 70.0, 200.0, 50.0); g2.draw(body); Shape leftWheel = // xcoord, ycoord, width, height new Ellipse2D.Double(50.0, 110.0, 50.0, 50.0); g2.setColor(Color.BLACK); g2.fill(leftWheel); // 30.0, 70.0: upper left corner Font aFont = new Font("SansSerif", Font.BOLD, 16); g2.setFont(aFont); g2.setPaint(Color.MAGENTA); g2.drawString("A car with no top", 45, 180);
12
12 Drawing So far… We know how to subclass a JPanel and use a Graphics2D object as a drawing canvas inside the paintComponent method. Sometimes we need to use an existing image rather than draw something ourselves
13
13 Drawing Drawing an Image Java’s Image class in java.awt abstracts a bitmap image for use in drawing. Images can be drawn to a panel through a Graphics object An important Graphics2D method: drawImage But first…
14
14 Drawing How do we load an image? java.awt contains a method that returns an image from a file on your disk Image img = ImageIO.read(new File("fileName")); Once we have an image and a graphics object, we can draw it // some other drawing code // 'g2' is a Graphics context object and img // is an initialized Image. 12 is x, 24 is y pixels g.drawImage(img, 12, 24, null);
15
15 Drawing Drawing Our Image This code will draw img at the coordinates (12, 24) on the panel The final ‘null’ is for an ImageObserver object, which we'll not need
16
16 Drawing Summary To draw a jpg or gif image 1. Extend JPanel 2. Declare Image instance variables in that class 3. Let the constructor initialize 4. Overide paintComponent 5. Call super.paintComponent() 6. get a Graphics2D object named g2 perhaps 7. send drawImage messages to g2
17
17 Drawing Example code that needs 6 jpg files in images public class CardsOnTheWater extends JPanel { private Image ocean, card1, card2, card3, card4, card5; public CardsOnTheWater() { try { ocean = ImageIO.read(new File("images/ocean.jpg")); card1 = ImageIO.read(new File("images/14h.jpg")); card2 = ImageIO.read(new File("images/13h.jpg")); card3 = ImageIO.read(new File("images/12h.jpg")); card4 = ImageIO.read(new File("images/11h.jpg")); card5 = ImageIO.read(new File("images/10h.jpg")); } catch (IOException e) { e.printStackTrace(); }
18
18 Drawing This method is called when the panel needs to be redrawn @Override public void paintComponent(Graphics g) { Graphics2D g2 = (Graphics2D) g; g2.drawImage(ocean, 0, 0, null); g2.drawImage(card1, 10, 10, null); g2.drawImage(card2, 30, 15, null); g2.drawImage(card3, 50, 20, null); g2.drawImage(card4, 70, 25, null); g2.drawImage(card5, 90, 30, null); }
Similar presentations
© 2024 SlidePlayer.com. Inc.
All rights reserved.