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Java Graphics Objectives To understand Graphics contexts and objects To be able to manipulate colours and fonts

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Java Graphics Objectives To understand Graphics contexts and objects To be able to manipulate colours and fonts To be able to understand and use the Graphics methods The Co-ordinate System (0,0) X axis (x,y) Y axis Graphics Contexts and Graphics Objects

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Presentation Transcript
slide1

Java Graphics

  • Objectives
  • To understand Graphics contexts and objects
  • To be able to manipulate colours and fonts
  • To be able to understand and use the Graphics methods
slide2

The Co-ordinate System

(0,0)

X axis

(x,y)

Y axis

slide3

Graphics Contexts and Graphics Objects

A Java Graphics Context enables drawing on the screen.

A Graphics object manages a context by controlling how information

is drawn.

Consider the following method found in Applets:

public void paint(Graphics g)

g represents a reference to the Graphics object managing the applets

graphics context.

The paint methods is not often used directly by the programmer.

slide4

Should a programmer need to force paint, a call to the repaint method

may be made.

repaint() ;

This makes a call to the component’s update method which will

call paint directly

Colour Control

Colours are defined and manipulated in Java through class Color.

Constant colour values are defined in this class. New colours may be

defined using RGB values:

Color c = new Color(128, 128, 128) ;// Gray

slide5

Displaying Colours in an Applet

import java.awt.*;

import javax.swing.*;

public class ShowColours extends JApplet

{ public void paint(Graphics g)

{ // set new colour using integers

g.setColor( new Color(255, 0 , 0) ) ;

g.fillRect(25, 25, 100, 20) ;

g.drawString( "Current RGB: "+g.getColor(),

130, 40) ;

// set new drawing color using static colour objects

g.setColor(Color.blue) ;

g.fillRect(25, 50, 100, 20) ;

g.drawString( "Current RGB: "+g.getColor(),

130, 65) ;

}

}

slide6

Font Control

import javax.swing.*;

import java.awt.*;

public class FontTest extends JApplet

{ public void paint(Graphics g)

{ // set font to Serif (Times), bold, 12pt

g.setFont( new Font("Serif", Font.BOLD, 12) ) ;

g.drawString( "Serif 12 point bold.", 20, 50) ;

// set font to monspaced (courier), italic, 24pt

g.setFont( new Font("Monospaced",Font.ITALIC,24));

g.drawString( "Monospaced 24 point italic.",20,70);

// set font to Serif, bold+italic, 24pt

g.setFont( new Font("Serif", Font.BOLD+Font.ITALIC,

24) ) ;

g.drawString( "Serif 24 point bold and italic.",

20, 90) ;

}

}

slide7

Font Metrics

Class FontMetrics defines methods which provide measurement

information about a font.

Font f = ……

FontMetrics fm = f.getFontMetrics() ;

int a = fm.getAscent() ;

int d = fm.getDescent() ;

int h = fm.getHeight() ;

leading

Xy1Ô

height

ascent

descent

slide8

Lines, Rectangles and Ovals

public void drawLine(int x1, int y1, int x2, int y2)

g.drawLine(10,10,20,20) ;

public void drawRect(int x, int y, int width, int height)

g.drawRect(10,10,20,20) ;

public void fillRect(int x, int y, int width, int height)

g.fillRect(10,10,20,20) ;

public void drawRoundRect(int x, int y, int w, int h,

int aw, int ah)

g.drawRoundRect(10,10,20,20,5,5) ;

slide9

import javax.swing.*;

import java.awt.*;

public class GraphicsTest extends JApplet

{ public void paint(Graphics g)

{ g.drawLine(10,10,20,20) ;

g.drawRect(10,40,20,20) ;

g.fillRect(10,70,20,20) ;

g.drawRoundRect(10,100,20,20,5,5) ;

g.drawRoundRect(10,130,100,100,20,20) ;

g.drawOval(10,210,20,20) ;

g.fillOval(10,240,20,20) ;

}

}

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