Java
TOPIC 11 –GRAPHICS FUNCTIONS

LESSON NOTE

GOAL

The goal of this lesson is to continue to develop your understanding of using function prototypes all while learning a little bit about computer graphics.

NOOPDraw.java

To do this, you will use a library called NOOPDraw.java which is a file that provides you with functionality to create a window and draw in it by doing simple function calls. To use this file, you will have to bring it into your project. The easiest way is to go on our website in the Resource section and copy and paste all the code into a class called NOOPDraw.java.

This file is available for download in the Resource section of this course.

Graphics in Java make use of object orientated programming (OOP). However, this file hides all OOP concepts from the programmer and is therefore called NOOPDraw, short for No OOP Draw. Students in the course will learn about OOP concepts later on in the course.

FIRST STEP – CREATING THE WINDOW

The first step when using NOOPDraw is to create the window. The createWindow() function does this for you. There are three versions (function overloading) that you can use.

public static void createWindow()

public static void createWindow(int width, int height)

public static void createWindow(int width, int height, String title)

The window above was created using:

NOOPDraw.createWindow(300, 200);

COORDINATE SYSTEM

In Java, the origin (0,0) is found that the top left of the window. As expected, the x coordinate increases as you go to the right. However, unlike in math class, the y coordinate increases as you go downwards.

DRAWING FUNCTIONS

Here is a full listing of drawing functions as of version 0.9:

public static void drawString(String s, double x, double y)

Draws the string s at coordinates (x,y).

public static void drawEllipse(double x, double y, double w, double h)

Draws ellipse of specified width and height with the top left of the bounding box at (x,y).

public static void fillEllipse(double x, double y, double w, double h)

Draws filled ellipse of specified width and height with the top left of the bounding box at (x,y).

public static void drawRectangle(double x, double y, double w, double h)

Draws rectangle of specified width and height with top left corner at (x,y).

public static void fillRectangle(double x, double y, double w, double h)

Draws filled rectangle of specified width and height with top left corner at (x,y).

public static void drawLine(double x1, double y1, double x2, double y2)

Draws lines from (x1, y1) to (x2, y2).

public static void drawTriangle(double x1, double y1, double x2, double y2, double x3, double y3)

Draws triangle with three specified points (x1, y1), (x2, y2) and (x3, y3).

public static void fillTriangle(double x1, double y1, double x2, double y2, double x3, double y3)

Draws filled triangle with three specified points (x1, y1), (x2, y2) and (x3, y3).

EXAMPLE

Here is a small program that makes use of the drawEllipse and fillEllipse functions:

THE CODE

THE RESULT

FUNCTIONS TO CHANGE DRAWING STYLE

Here is a list of functions that allow you to alter how the drawing occurs:

public static void setBrushSize(double r)

Sets the size of the drawing brush to a radius of r.

public static void setColor(int r, int g, int b)

Sets the drawing color created by rgb.

public static void setColor(String s)

Sets the drawing color created by a color’s name inserted in a String. For example, you can provide “black” or “green”.

EXAMPLE

Here is the same example as above but with different colours.

THE CODE

THE RESULT

SAVING TO FILE

You can also save your image to a file. All you need to do is provide a filename. The file will automatically be saved in the project folder.

public static void save(String filename)

Saves the image to a file in the project folder. The filename has to end with either .jpg, .gif or .png for this to work.