Chapter 15Java: an Introduction to Computer Science & Programming - Walter Savitch 1 Chapter 15 l...

Chapter 15 Java: an Introduction to Computer Science & Programming - Walter Savitch 1

Chapter 15

Basic Figures Colors Fonts and Other Text Details

Graphics Objects


Earlier chapters explain how to make graphical user interfaces (GUIs).

This chapter explains a different way of using graphics in Java: drawing pictures.

We will learn how to basic figures such as lines, ovals, and rectangles.

Basic figures can be combined to create elaborate pictures.

An optional section explains how to draw polygons.

Basic Figures


Screen Coordinate System

(0, 0)

origin

Y-coordinate is positive and increasing in the downward direction.

X-coordinate is positive and increasing to the right.

All coordinates are normally positive.



(100, 75)

(0, 0)

origin

X-coordinate:100 pixels from left edge of screen

Y-coordinate:75 pixels from top edge of screen

Location of a rectangle is specified by coordinates of upper left corner.



(100, 75)

(0, 0)

origin

Location of an oval is specified by a tightly fitting rectangle.


The paint Method

Most Swing and Swing related components have a method named paint.

The paint method draws the component on the screen.

To draw basic figures such as ovals and rectangles, you need to redefine the paint method.

The paint method is called automatically and should not be invoked in the programmer’s code.


public void paint(Graphics g)

{

super.paint(g);

g.drawOval(X_FACE, Y_FACE, FACE_DIAMETER, FACE_DIAMETER);

//Draw Nose:

g.fillOval(X_NOSE, Y_NOSE, NOSE_DIAMETER, NOSE_DIAMETER);

//Draw Eyes:

g.fillOval(X_LEFT_EYE, Y_LEFT_EYE, EYE_WIDTH, EYE_HEIGHT);

g.fillOval(X_RIGHT_EYE, Y_RIGHT_EYE, EYE_WIDTH, EYE_HEIGHT);

//Draw eyebrows:

g.drawLine(X1_LEFT_BROW, Y1_LEFT_BROW,

X2_LEFT_BROW, Y2_LEFT_BROW);

g.drawLine(X1_RIGHT_BROW, Y1_RIGHT_BROW,

X2_RIGHT_BROW, Y2_RIGHT_BROW);

//Draw Mouth:

g.drawArc(X_MOUTH, Y_MOUTH, MOUTH_WIDTH, MOUTH_HEIGHT,

MOUTH_START_ANGLE, MOUTH_ARC_SWEEP);

}

The complete paint method from Madeleine.java

The program draws this picture.



{

super.paint(g);


//Draw Nose:


//Draw Eyes:



//Draw eyebrows:





//Draw Mouth:



}

The face, nose, and eyes are ovals. The eyebrows are lines, and the mouth is an arc.

The method for drawing each shape has numeric parameters telling where to draw the shape and how big to make it.



{

super.paint(g);


//Draw Nose:


//Draw Eyes:



//Draw eyebrows:





//Draw Mouth:



}

The paint method receives one parameter, which is an object of the Graphics class.

The Graphics parameter is the calling object for all of the methods that draw lines and shapes.

Calling the paint method of the parent class is a good programming practice.


The Graphics class

Contains methods used to draw basic shapes and lines Is part of the AWT package (or library) so the AWT must be

imported:

import java.awt.*; Most methods for painting shapes have two versions:

» A draw version which only draws the outline of the shape

drawOval» A fill version which fills in the shape

fillOval


Drawing Rectangles and Ovals

(100, 120)

(0, 0)

g.fillOval(100, 120, 40, 20);

(100, 50)

width

height40

20

Graphics object

20

40

g.fillRect(100, 50, 40, 20);

X and Y coordinates of upper left corner


Drawing Arcs

An arc is specified by giving an oval and then specifying what portion of the oval will be used for the arc.

To tell which part of the oval will be used, specify the beginning angle and the degrees of the sweep.

positive direction

0 degrees

width

height

(x,y)

gdrawArc(x, y, width, height, 0, 360);


Arc Examples

positive direction

0 degrees

negative direction

0 degrees

180 degrees

gdrawArc(x, y, width, height, 0, -90);




plus 90 degrees


Round Rectangles

Round rectangle is a rectangle where corners have been replaced with arcs.

Specify by giving rectangle information and then height and width of corner arcs.

arcWidth

width

height

(x,y)

gdrawRoundRect(x, y, width, height, arcWidth, arcHeight);

arcHeight


Polygons

drawPolygon allows a program to draw shapes with any number of sides.

public void drawPolygon(int[] x, int[] y, int point)

Each point in the polygon will have an x coordinate from the first parameter and a y coordinate from the corresponding element of the second parameter.

The third parameter tells how many points the polygon will have. Always draws a closed polygon. If first and last points are not equal,

draws a line from last to first. drawPolyline is similar but can draw an open figure. fillPolygon is similar but fills with color instead of drawing outline.


Action Drawings and repaint

The SadMadeleine program demonstrates how a program can change a picture.

In the original picture, the face has a frown. When the user clicks on the button, the picture changes to a

smiling face and moves up on the screen.


Action Drawings and repaint

The actionPerformed method changes the smile variable that the paint method uses.

When the smile variable is changed to true, the paint method knows to draw a smile instead of a frown.

public void actionPerformed(ActionEvent e)

{

if (e.getActionCommand().equals("Click for a Smile."))

smile = true;

else

System.out.println("Error in button interface.");

repaint();

}


Action Drawings and repaint Unless the repaint method is called, the change will not be

shown on screen. The repaint method calls paint to update the picture. The paint methd should not be called directly.

public void actionPerformed(ActionEvent e)

{

if (e.getActionCommand().equals("Click for a Smile."))

smile = true;

else

System.out.println("Error in button interface.");

repaint();

}


Colors

Draw and fill methods like fillOval will use the current color. You can use the setColor method of a Graphics object to

change the current color. To draw a red mouth you could change the paint method of the

Madeleine program to include these lines:

//Draw Mouth:

g.setColor(Color.red);




Defining Colors

The Color class mixes amounts of red, green, and blue to produce a new color.

Since colors are made by combing different amounts of red, green, and blue, this is called the RGB color system.

The parameters to the Color constructor must be type int or float.

When integers are used as parameters to the Color constructor they should be in the range 0 to 255.

When floats are used as parameters to the Color constructor they should be in the range 0.0 to 1.0.

Color brown = new Color(204, 102, 0);


Fonts and Other Text Details

A font is a style of text. A program can use the drawString method to display text on

the screen. The first parameter tells which characters to display. The last two parameters to drawString are coordinates that

tell where on the screen to put the text.

g.drawString(theText, X_START, Y_START);


Setting the Font

The method setFont in a Graphics object can be used to change the current font.

Java guarantees that at least three fonts will be available:» Monospaced» SanSerif» Serif


Using the Font Constructor

To specify a font with a particular name, style, and size, use the Font constructor.

Size of the font is specified in points.

Each point is 1/72 of an inch, but point sizes are only approximate.

Font f = new Font(“Serif”, Font.BOLD|Font.ITALIC,

POINT_SIZE);

g.setFont(f);

Name of the font Style of the font: bold and italic

Size of the font in points (an integer)


Summary

You can draw figures such as lines, ovals, and rectangles using methods in the class Graphics.

You can specify the color of each figure drawn using the method setColor of the Graphics class.

You can define your own colors using the class Color. Colors are defined using the RGB (Red/Green/Blue) system. You can add text to a a graphics drawing by using the

Graphics method drawString. You can set the font and point size for a text written using

drawString with the Graphics method setFont.

Chapter 15Java: an Introduction to Computer Science & Programming - Walter Savitch 1 Chapter 15 l...

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