1. Java Software Solutions Lewis and Loftus Chapter 7 1 Copyright 1997 by John Lewis and William Loftus. All rights reserved. Graphics -- Introduction The use of graphics is common among modern software systems Java has strong API support for graphics in the java.awt (abstract windowing toolkit) package Chapter 7 focuses on: –the coordinate system for Java graphics –the use of color –drawing shapes such as lines, ovals, rectangles, etc. –the use of fonts –basic animation techniques

2. Java Software Solutions Lewis and Loftus Chapter 7 2 Copyright 1997 by John Lewis and William Loftus. All rights reserved. The Graphics Class An object of the Graphics class represents a particular drawing surface It defines a graphics context in which drawn shapes will be rendered The Graphics class contains methods for drawing various shapes and controlling visual aspects like font and color An applet has a graphics context, which is automatically passed to the paint method when it is called

3. Java Software Solutions Lewis and Loftus Chapter 7 3 Copyright 1997 by John Lewis and William Loftus. All rights reserved. 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 The top left corner of the area is coordinate A drawing surface has a particular width and height Anything drawn outside of that area will not be visible See Coordinates.java

4. Java Software Solutions Lewis and Loftus Chapter 7 4 Copyright 1997 by John Lewis and William Loftus. All rights reserved. The Coordinate System x y Y X

5. Java Software Solutions Lewis and Loftus Chapter 7 5 Copyright 1997 by John Lewis and William Loftus. All rights reserved. Color The Color class is used to define and manage the color in which shapes are drawn Colors are defined by their RGB value, which defines the relative contribution of the primary colors red, green, and blue Each drawing surface has a foreground color and a background color The setColor method of the Graphics class defines the foreground color, and the setBackground method of the component (the applet) sets the background color

6. Java Software Solutions Lewis and Loftus Chapter 7 6 Copyright 1997 by John Lewis and William Loftus. All rights reserved. Color The Color class contains several predefined colors, defined as public, static constants See Nature.java Many other colors can be defined using the constructor of the Color class Over 16 million colors can be defined, but humans cannot distinguish between many similar colors Furthermore, the hardware of most systems has limitations to the color options available

7. Java Software Solutions Lewis and Loftus Chapter 7 7 Copyright 1997 by John Lewis and William Loftus. All rights reserved. XOR Mode Drawing in normal mode causes shapes of the same color to blend together Drawing in XOR mode causes the overlapping portions of the shapes to be rendered in a contrasting color This effect can be used to "erase" a shape by redrawing it in the same color in the same spot while in XOR mode See XOR_Demo.java

8. Java Software Solutions Lewis and Loftus Chapter 7 8 Copyright 1997 by John Lewis and William Loftus. All rights reserved. Drawing Shapes The Graphics class contains methods for drawing several specific shapes: lines, ovals, rectangles, arcs, polygons, and polylines Most shapes can be drawn filled or unfilled A line, drawn with the drawLine method, is always one pixel wide and cannot be filled

9. Java Software Solutions Lewis and Loftus Chapter 7 9 Copyright 1997 by John Lewis and William Loftus. All rights reserved. Ovals An oval is defined by its bounding rectangle: The methods that draw an oval take four parameters, all integers: drawOval (x, y, width, height) fillOval (x, y, width, height) width height

10. Java Software Solutions Lewis and Loftus Chapter 7 10 Copyright 1997 by John Lewis and William Loftus. All rights reserved. Ovals The first two parameters are the coordinate of the top-left corner of the bounding rectangle The third and fourth parameters specify the width and height of the bounding rectangle The drawOval method draws an unfilled oval and the fillOval method draws a filled (opaque) oval See Ovals.java and Rotating_Disk.java

11. Java Software Solutions Lewis and Loftus Chapter 7 11 Copyright 1997 by John Lewis and William Loftus. All rights reserved. Rectangles Rectangles can be drawn –filled or unfilled –with squared or rounded corners –with a slight three-dimensional effect or not The primary parameters for all rectangle drawing methods define the upper left corner of the rectangle and its width and height The shape of the rounded corner of a rounded rectangle are defined by an arc width and height

12. Java Software Solutions Lewis and Loftus Chapter 7 12 Copyright 1997 by John Lewis and William Loftus. All rights reserved. Rectangles A three dimensional rectangle is shown using a small highlight on two sides of the rectangle The highlight appears on the bottom and right or the top and left as specified by a boolean parameter to the 3D drawing methods See Rectangles.java, Rounded_Rectangles.java, and Three_D_Rectangles.java

13. Java Software Solutions Lewis and Loftus Chapter 7 13 Copyright 1997 by John Lewis and William Loftus. All rights reserved. Arcs An arc is defined as a segment of an oval The first four parameters to the arc drawing methods define the bounding rectangle of the oval (top left corner, width, and height) The other two parameters define the start angle and the arc angle The start angle indicates where the arc begins and the arc angle determines how far the arc sweeps across its defining oval See Arc.java

14. Java Software Solutions Lewis and Loftus Chapter 7 14 Copyright 1997 by John Lewis and William Loftus. All rights reserved. Arcs The start angle can be specified using both positive and negative values: 90 -270 45 -315 0 360 -360 270 -90 180 -180

15. Java Software Solutions Lewis and Loftus Chapter 7 15 Copyright 1997 by John Lewis and William Loftus. All rights reserved. Arcs An arc angle can also be positive or negative A positive arc angle sweeps counterclockwise, and a negative arc angle sweeps clockwise Therefore, the same arc can be specified using four different combinations of start and arc angles Arcs can also be filled or unfilled See Arcs.java

16. Java Software Solutions Lewis and Loftus Chapter 7 16 Copyright 1997 by John Lewis and William Loftus. All rights reserved. Polygons A polygon is a multisided figure defined by a series of ordered points Line segments connecting the points form the polygon The points are defined by corresponding arrays of x and y coordinate values, and can already be incorporated into an object of the Polygon class Polygons are closed, forming a line segment from the last point back to the first See Polygons.java

17. Java Software Solutions Lewis and Loftus Chapter 7 17 Copyright 1997 by John Lewis and William Loftus. All rights reserved. Polylines A polyline is similar to a polygon except that it is not closed That is, there is no line segment from the last point back to the first unless explicitly specified They are convenient for specifying certain kinds of complex shapes Polylines cannot be filled See Polylines.java

18. Java Software Solutions Lewis and Loftus Chapter 7 18 Copyright 1997 by John Lewis and William Loftus. All rights reserved. Fonts A font defines the look of each character when it is printed or drawn The Font class provides methods for specifying fonts in a Java program Each computer system supports a specific set of fonts See Font_Lister.java The setFont method defines the current font for a program

19. Java Software Solutions Lewis and Loftus Chapter 7 19 Copyright 1997 by John Lewis and William Loftus. All rights reserved. Fonts A font is defined using the Font class constructor and a combination of: –font name –font style: plain, bold, italic, or bold+italic –font size, in points Constants are defined in the Font class to specify the font style See Entropy.java

20. Java Software Solutions Lewis and Loftus Chapter 7 20 Copyright 1997 by John Lewis and William Loftus. All rights reserved. Animations Simple animations can be accomplished by drawing a shape, then erasing it, then drawing it again in a slightly altered position Erasing can be accomplished through careful use of XOR mode Timing must be controlled so that the animation does not move too fast See Bouncing_Ball.java