2D graphics in Java

1
2D graphics in Java
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java.awt.Component

• Java included basic graphics capabilities as part
  of the AWT (Abstract Windowing Toolkit).
• All graphics operations in Java are performed
  using a java.awt.Graphics object. The Graphics
  object serves three purposes
• it represents the drawing surface. A Graphics
  object is used to draw into a java.awt.Component
  on the screen, to draw into an off-screen
  java.awt. Image, or to send graphics to a
  printer.
• It maintains the current state of graphics
  attributes, such as the current drawing color,
  font, and clipping region.
• It defines methods that perform various graphics
  operations, such as drawing lines, rendering
  strings of text, and copying the content of Image
  objects onto the drawing surface.

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Lines

• To draw a line at a particular location on the
  screen, we use the method
• java.awt.Graphics.drawLine(int x1, int y1, int
  x2, int y2)

4
Plotting Points

• The Java language does not offer any way to draw
  points (pixels) but we can achieve it by using
  the drawLine() method like this
• java.awt.Graphics.drawLine(int x1,
  int y1, int x1, int y1)
• That is, we use the same starting point and the
  ending point for x1 and y1. For example to plot a
  point at the 10 by 15 pixels away from the origin
  use
• java.awt.Graphics.drawLine(10, 15, 10,
  15)

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Rectangles

• The drawRect() method draws an outline rectangle.
  The left and right edges of the rectangle are at
  x and x  width. The top and bottom edges are at
  y and y  height.
• java.awt.Graphics.drawRect(int x1, int
  y1, int width, int height)
• To draw a filled rectangle we use the method
• java.awt.Graphics.fillRect(int x1, int
  y1, int width, int height)
• To draw a square 50 by 50 pixels away from the
  origin use
• java.awt.Graphics.drawRect(50, 50, 100,
  100) This will give us a rectangle starting from
  the point (50, 50) and extending up to the point
  (150, 150)

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Circles and Ovals

• This method draws a circle or an ellipse such
  that it fits within the rectangle specified by
  the x, y, width and height arguments. The center
  of the oval is the center of the rectangle. When
  the value of width and height are equal we end up
  with a circle and when they are not equal we end
  up with an oval.
• java.awt.Graphics.drawOval(int x, int
  y, int width, int height)
• To draw a circle at the center of the origin with
  the radius of 50 pixels, use the following
  values
• java.awt.Graphics.drawOval(60, 60, 50,
  50)
• The following will draw an oval with the
  center at 100, 100 with a radius of 50 for x and
  80 for y
• java.awt.Graphics.drawOval(50,
  20, 50, 100) )

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Arcs and Wedges

• To draw a circular or elliptical arc use the
  method
• java.awt.Graphics.drawArc(int x, int y,
  int width, int height, int startAngle, int
  arcAngle)
• The center of the arc is the center of the
  rectangle whose origin is (x, y) and whose size
  is specified by the width and height arguments.
  The two axes of the arc are given by the width
  and height arguments. The arc is drawn from
  startAngle to startAngle arcAngle.
• The start angle and arc angle are in degrees, not
  radians. A start angle of 0 indicates the
  3-o'clock position. A positive arc angle
  indicates a counter-clockwise rotation a
  negative arc angle indicates a clockwise
  rotation.
• To draw a filled arc use the method
• java.awt.Graphics.fillArc(int x, int
  y, int width, int height, int startAngle, int
  arcAngle)

8
Clearing an area on the Screen

• To wipe out and clean everything (or part of a
  rectangular area) of the screen with the
  background color use the method
• java.awt.Graphics.clearRect(int x, int y,
  int width, int height)

9
Drawing Text

• To write text/string on the screen we must use a
  special method to do so. The method that we used
  last week (System.out.print()) won't work as that
  method is not graphical.
• Java offer a method to draw string in graphic
  mode, this method is
• java.awt.Graphics.drawString(String s, int
  x, int y)
• s is the text/string that we want to draw. x
  and y are the location on the screen where the
  text/string should be drawn. For example
• g.drawString("Hello, Java", 290, 240)

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Color

• colors are represented by the java.awt.Color
  class.
• Color such as Color.black and Color.white.
• example
• java.awt.Graphics.setColor(Color.blue)

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Example

• //program to draw vertical line
• import java.awt.
• import java.awt.event.
• import java.util.
• //this frame appears on your secreen and goes
  away when you close it
• //use it to paint the 2d
• public class vline extends Frame
• public static void main(String args)new
  vline()
• vline()
• //name of frame
• super("draw line")
• addWindowListener(new WindowAdapter()
• public void windowClosing(WindowEvent
  e)System.exit(0))
• //size of frame
• setSize(640, 230)
• add("Center", new verline())
• show()

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Example

• class verline extends Canvas
• void showGrid(Graphics g)
• g.setColor(Color.blue)
• int x10 int y10
• for(int i1ilt100i)
• g.drawLine(x, y, x, y)
• y
• public void paint(Graphics g)
• showGrid(g)