Lecture 3 A First Graphic Program

1. Lecture 3 A First Graphic Program

2. Features of a simple graphic program

3. Gapp and Gcanvas are ours – Are New Developed. • Inherited from JFrame and panel which are part of the Java Foundation Classes - in particular they are part of the swing” GUI components. • when a Gapp object is created, a new GUI window appears on the screen. Features of a simple graphic program

4. A Gcanvas/JPanel is simply something we can draw on, but it isn’t allowed to be on screen by itself, it must be part of a JFrame. So what we actually need is an instance of Gapp with an instance of Gcanvas “inside” it (Figure 23). Features of a simple graphic program

5. Main() The main entry point for the system is in class Gapp. simple graphic program – Main()

6. sets the window’s screen position and size • (lines 22,23), sets up some Java apparatus to allow the program to shut down cleanly. • (lines 27-31) and creates an instance of a Gcanvas (graphics canvas) . • line 25. This GCanvas object is “added” to the Gapp object and hence becomes part of that window. simple graphic program- initComponents()

7. it is passed a Graphics object (“g”) - line 12. • drawLine() which is a member of the Graphics class. • The Graphics class is part of the standard Java class library and its member functions are termed “graphics primitives”. • There exist a whole range of methods for drawing and coloring in a variety of shapes (boxes, polygons, ovals etc.) • Take a look at the Java API documentation for full details. simple graphic program- Paintcomponent()

8. simple graphic program- Paintcomponent() The drawLine() method takes 4 parameters, x1, y1, x2, y2 which represent the start and end points of the line you wish to draw.

9. First Program

10. First Program

11. First Program

12. First Program

13. First Program - Running

14. A graphics primitive is a drawing function which the system makes available to the applications programmer. Example is the Java “drawLine()” method. Graphics Primitives

15. Graphics Primitives

16. Graphics Primitives

17. Graphics Primitives

18. Graphics Primitives