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

1. 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

2. The Co-ordinate System (0,0) X axis (x,y) Y axis

3. 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.

4. 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

5. 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) ; } }

6. 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) ; } }

7. 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

8. 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) ;

9. 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) ; } }