Lecture 7 A First Graphic Program And Data Structures & Drawing

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1 Lecture 7 A First Graphic Program And Data Structures & Drawing

2 Objective The objective is that you will understand: How to program the generation of 2D and 3D images. How to manipulate those images through Scaling, translation, rotation and projection. How to color and shade the images. Remove hidden surfaces and create realistic lighting effects. Before any of that however, we must learn more about how to describe a drawing in terms that a computer can understand.

3 Graphics Primitives A graphics primitive: is a drawing function which the system makes available to the applications programmer. Example is the Java drawline() method. 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.

4 Features of a simple graphic program Gapp and Gcanvas 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.

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

6 simple graphic program- initcomponents() 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.

7 simple graphic program- Paintcomponent() it is passed a Graphics object ( g ) - line 12. drawline() which is a member of the Graphics class. The drawline() method takes 4 parameters, x1, y1, x2, y2 which represent the start and end points of the line you wish to draw.

8 abstract void drawline( int x1, int y1, int x2, int y2) abstract void drawoval( int x, int y, int width, int height) abstract void drawpolygon( int[] xpoints, int[] ypoints, int npoints) abstract void drawpolyline(int[] xpoints, int[] ypoints, int npoints) void drawrect(int x, int y, int width, int height) abstract void drawroundrect(int x, int y, int width, int height, int arcwidth, int archeight) abstract void drawstring(attributed- CharacterIterator iterator, int x, int y) Graphics Primitives Draws a line, using the current color, between the points (x1, y1) and (x2, y2) in this graphics context's coordinate system. Draws the outline of an oval. Draws a closed polygon defined by arrays of x and y coordinates. Draws a sequence of connected lines defined by arrays of x and y coordinates. Draws the outline of the specified rectangle. Draws an outlined round cornered rectangle using this graphics context's current color. Draws the text given by the specified iterator, using this graphics context's current color.

9 void fill3drect( int x, int y, int width, int height, boolean raised) abstract void fillarc(int x, int y, int width, int height, int startangle, int arcangle) abstract void filloval(int x, int y, int width, int height) abstract void fillpolygon(int[] xpoints, int[] ypoints, int npoints) abstract void fillrect(int x, int y, int width, int height) abstract void fillroundrect(int x, int y, int width, int height, int arcwidth, int archeight) abstract void clearrect(int x, int y, int width, int height) abstract void cliprect(int x, int y, int width, int height) abstract void copyarea(int x, int y, int width, int height, int dx, int dy) Graphics Primitives Paints a 3-D highlighted rectangle filled with the current color. Fills a circular or elliptical arc covering the specified rectangle. Fills an oval bounded by the specified rectangle with the current color. Fills a closed polygon defined by arrays of x and y coordinates. Fills the specified rectangle. Fills the specified rounded corner rectangle with the current color. Clears the specified rectangle by filling it with the background color of the current drawing surface. Intersects the current clip with the specified rectangle. Copies an area of the component by a distance specified by dx and dy.

10 Process of Generating Graphic Image

11 Point 2d Class A point is basically two coordinates, x and y, which are real numbers. Point2d is a Java class to represent a point and used to store the x and y coordinates of the point.

12 The Basic 2d data structure Line2d Class Lines are the basic item of drawings. Each line has two end points. This suggests that an appropriate way to describe the drawings would be in terms of two classes: Line2d and Point2d. Thus to represent L1 in this scheme, we need 3 objects:

13 Line2d Class The square has 4 corners (nodes). Notice in the drawing that a line is defined between two nodes ( for example line L1 connects nodes N1 and N2 ) but not all nodes are connected by lines (for example N1 is not connected to N3). The square have 4 nodes and 8 Point2d. Duplicating Data.

14 Line2d Class Is Duplication necessary? Well, yes and no. You can do it using 4 points and save your self 4 objects, but that means that those lines share instances of the points and CAN NEVER BE CHANGED INDEPENDANTLY. From a data modeling point of view, the corners of the square are in fact two points that JUST HAPPEN to be in the same place.

15 The Basic 2d data structure Line2d Class

16 Shape2d Class Can be described as a collection of lines. is a class which maintains a list of all of the lines that make up a shape (vector of lines). numberoflines describes how many lines make up our shape.

17 The Basic 2d data structure Shape2d

18 Drawing2d Class A drawing can consist of many shapes - We can therefore add a final class to our data model: Drawing2d, which can maintain another list (Vector) of the various shapes.

19 Drawing2d Class

20 The Basic 2d data structure Summary So, in full, we have a drawing object, which has a list of shape objects, which have lists of line objects, which have two point objects each.

21 The Basic 2d data structure Class Diagram Drawing2d has Many Shapes Shape2d has many Lines Line2d has tow points

22 A working Gcanvas

23 The Completed system of a graphic program The final class diagram of the system should look something like this.

24 Exercises

25 Exercises

26 Exercises 1. Describe the structure of simple graphics program? 2. List the basic operations that can be performed using the initiatecomponent() In the Gapp class? 3. What is graphics primitive? 4. List at least five graphics primitive, determine the required parameter, and the job function required? 5. How can a program generate image or drawing on the computer screen? 6. Describe the following data structures: Point2d - Line2d - Shape2d - Drawing2d 1. Describe the structure of simple graphics program? 2. For the following figures: Draw the class diagram. Represent these figures in format like outstaring format?

Graphics Applets. By Mr. Dave Clausen

Graphics Applets. By Mr. Dave Clausen Graphics Applets By Mr. Dave Clausen Applets A Java application is a stand-alone program with a main method (like the ones we've seen so far) A Java applet is a program that is intended to transported