Graphics%20Class

1
Graphics Class

• Graphics class is a class in java.awt package.
• contains methods for creating line drawings,
  rectangles, ovals, arcs, polygons.
• control color and fonts
• A Graphics object represents a particular drawing
  surface.
• We cannot directly call the constructor of
  Graphics class to create a Graphics object.
• A Graphics object is created indirectly. For
  example, each applet is associated with a
  Graphics object, and we can access this Graphics
  object.
• Any methods called with the Graphics object
  associated with an applet will affect that
  applet.
• An object of Graphics class represents a
  particular drawing surface, and Graphics class
  contains methods for drawing shapes on that
  surface.

2
An Applets Graphics Context

• An applet has a graphics context which is
  automatically passed to the paint method when it
  is invoked.
• import java.applet.Applet
• import java.awt.
• public class AnApplet extends Applet
• public void paint(Graphics g)
• // using this Graphics object g,
• // we can draw shapes on this applet.

3
Coordinate System

• 0,0
• width drawing surface of
• an applet
• height
• width-1,height-1
• Each point on the coordinate system represents a
  single pixel.
• Anything drawn outside of this area will not be
  visible.

4
An Example

• import java.applet.Applet
• import java.awt.
• public class AnApplet extends Applet
• public void paint(Graphics g)
• g.drawRect(10,10,100,50)
• top left corner width and height of the
  rectangle
• g.drawLine(10,10,110,60)
• source coordinate destination coordinate
• g.drawString(This a rectangle,10,150)
• top left corner

5
Drawing Shapes

• Graphics class directly supports the drawing of
• lines
• ovals (circles are special forms of ovals)
• rectangles
• arcs
• polygons triangles, hexagons,
• polylines a series of line segments
• Most shapes (except polylines) can be drawn
  filled or unfilled.
• We can see the other graphics objects under an
  unfilled object
• The foreground color is used to fill shapes. The
  other graphics objects under a filled object
  cannot be seen.
• Thickness cannot be specified (always 1 pixel).
  Thicker lines can be drawn by multiple lines.
• g.drawLine(10,10,200,10)
• g.drawLine(10,11,200,11)

6
Rectangles

• drawRect(xsrc,ysrc,width,height)
• fillRect(xsrc,ysrc,width,height)
• top left corner

7
Ovals

• A bounding rectangle is used to define the
  position of an oval.
• drawRect(xsrc,ysrc,width,height)
• fillRect(xsrc,ysrc,width,height)
• top left corner of the bounding rectangle
• bounding rectangle is not seen
• if width and height are equal ? a circle

8
Some Other Rectangle Related Methods

• clearRect(x,y,width,height)
• draws a (filled) rectangle in the current
  background color.
• cleans that rectangle area.
• drawRoundRect(x,y,width,height,arcwidth,archeight)
  
• fillRoundRect(x,y,width,height,arcwidth,archeight)
  
• draws a rectangle with rounded corners.
• archeight
• arcwidth

9
Arcs

• An arc is a segment of an oval.
• The segment begins at a specific angle, and
  extends for a distance specified by the arc
  angle.
• drawArc(x,y,width,height,startangle,arcangle)
• fillArc(x,y,width,height,startangle,arcangle)
• -270,90
• counter-clockwise (positive)
• 180,-180 0,360,-360
• clockwise (negative)
• 270,-90

10
Arcs (cont.)

• startangle is in degrees
• a value between 0 and 360, or between 0 and -360
• arcangle
• positive (counter clockwise)
• negative (clockwise)
• drawArc(20,20,50,50,90,90)
• drawArc(20,20,50,50,-270,90)
• drawArc(20,20,50,50,180,-90)
• drawArc(20,20,50,50,-180,-90) same arc is drawn
  by all of them
• fillArc(20,20,50,50,90,90)

11
Polygons

• A polygon is a multi-sided figure
• A polygon is defined using a series of ltx,ygt
  points which indicates the end points of the
  sides of that polygon.
• Polygons are closed. It forms a line segment from
  the last point to the first.
• End points can be specified by
• two integer arrays or
• an object of Polygon class indicating the end
  points.
• drawPolygon(int xpoints, int ypoints, int
  numofpoints)
• fillPolygon(int xpoints, int ypoints, int
  numofpoints)
• drawPolygon(Polygon poly)
• fillPolygon(Polygon poly)

12
Polygons (cont.)

• int xs 50,100,150,100 100,50
• int ys 100,50,100,150
• drawPolygon(xs,ys,4)
• 50,100 150,100
• Polygon p new Polygon()
• p.addPoint(50,100)
• p.addPoint(100,50) 100,150
• p.addPoint(150,100)
• p.addPoint(100,150)
• drawPolygon(p)

13
Polyline

• A polyline is a similar to a polygon except it is
  not closed.
• There is no line segment from the last point to
  the first one.
• Polylines cannot be filled.
• int xs 50,100,150,100
• int ys 100,50,100,150
• drawPolyline(xs,ys,4)

14
Color Class

• Color class is used to define and manage the
  color in which shapes are drawn.
• We can control the color of the shapes we draw.
• A color is defined by an R G B value
  (red,green,blue) that specifies the relative
  contribution of these three primary colors red,
  green, blue (values between 0 to 255).
• Color class contains several final static Color
  objects to define basic colors.
• blue Color.blue 0,0,255
• green Color.green 0,255,0
• red Color.red 255,0,0
• black Color.black 0,0,0
• white Color.white 255,255,255
• yellow Color.yellow 255,255,0
• gray Color.gray 128,128,128

15
Color Class (cont.)

• In addition to basic colors defined in Color
  class, we can define our own color by setting
  these three values (2563 almost 16 million
  different colors).
• Color mycolor new Color(100,100,100)
• We can change foreground (colors of shapes) and
  background (general color of the applet) colors.
  In paint method,
• setBackground(Color.white)
• changes the background color to white.
  setBackground is a method of Applet class.
• g.setColor(Color.red)
• changes the foreground color to red. setColor is
  a method of Graphics class.

16
Color Class - Example

• public void paint (Graphics g)
• setBackground(Color.white) ? background is
  white
• g.setColor(Color.yellow) ? color of pen is
  yellow
• g.drawString(This is yellow,20,20) ? This
  is yellow
• g.setColor(Color.blue) ? color of pen is blue
• g.drawLine(20,50,200,50) ?
• g.setColor(Color.green) ? color of pen is green
• g.drawRect(20,100,200,100) ?

17
Fonts

• A font defines the look of each character when it
  is printed or drawn.
• Font class provides methods for specifying fonts
  in a Java program.
• There is a specific set of fonts in each system.
  We can use one of the fonts from this list.
• Using the constructor of Font class we can create
  a Font object.
• Then we can set the current font to this Font
  object using setFont method in Graphics class.
• new Font(fontname,style,size)
• TimesRoman Font.PLAIN 12 14 16 18 20
• Helvetica Font.BOLD
• Font.ITALIC

18
Fonts -- Example

• import java.applet.Applet
• import java.awt.
• public class FontTest extends Applet
• public void paint(Graphics g)
• g.setFont(new Font("TimesRoman",Font.PLAIN,16)
  )
• g.drawString("Font is TimesRoman-PLAIN-16",10,
  30)
• ? Font is TimesRoman-PLAIN-16
• g.setFont(new Font("TimesRoman",Font.ITALIC,20
  ))
• g.drawString("Font is TimesRoman-ITALIC-20",10
  ,60)
• ? Font is TimesRoman-ITALIC-20
• g.setFont(new Font(Courier",Font.BOLDFont.ITA
  LIC,20))
• g.drawString("Font is Courier-BOLD-ITALIC-20",
  10,90)
• ? Font is Courier-BOLD-ITALIC-20
• g.setFont(new Font("Courier",Font.PLAIN,16))
• g.drawString("Font is Courier-PLAIN-16",10,120
  )
• ? Font is Courier-PLAIN-16

19
GraphicsTest

• import java.applet.Applet
• import java.awt.
• public class GraphicsTest extends Applet
• public void paint(Graphics g)
• resize(600,400)
• g.drawRect(10,10,200,100)
• g.drawLine(10,10,210,110)
• g.drawLine(10,110,210,10)
• g.drawString("This is a rectangle",10,130)
• g.setColor(Color.red)
• g.drawString("A red string",10,150)
• g.setColor(Color.blue)
• g.drawString("A blue string",10,170)
• g.fillRect(300,10,100,50)
• g.drawOval(300,100,100,50)
• g.fillOval(300,200,100,50)
• g.drawOval(300,300,40,40)
• g.fillOval(350,300,40,40)

20
Output of GraphicsTest