Using Graphics in Java

1
Using Graphics in Java

• CSE301
• University of Sunderland
• Harry R Erwin, PhD

2
Resources

• Flanagan, David (2000). Java Foundation Classes
  in a Nutshell, OReilly.
• Darwin, Ian F. (2004). Java Cookbook, OReilly.
• Flanagan, David (2004). Java Examples in a
  Nutshell, OReilly.

3
Goals

• The goal of these two lectures is to provide the
  student an understanding of graphics in Java.
• GUI1 explores the Java 2D API, the basic graphics
  primitives.
• GUI2 explores image processing, image I/O, and
  animation.

4
Topics

• Gotchas in Java graphics
• Graphics in Swing
• Graphics2D
• Image Processing
• Image I/O
• Animation

5
Gotchas in Java graphics

• Dont use both the fill and draw methods for a
  shape unless you need the outline and interior to
  be different colours.
• Override the paint() or paintComponent() (in
  Swing) method to draw anything.

6
Graphics in Swing

• Basically similar to AWT, but
• Override paintComponent(Graphics g) instead of
  paint(Graphics g). This handles interaction with
  borders and similar graphical elements better.
• The first thing paintComponent(Graphics g) should
  do is call super.paintComponent(g)
• Note this is different from paint(Graphics g),
  which should not call super.paint(g)

7
Graphics2D

• See Knudsen J. Java 2D Graphics, OReilly.
• Graphics2D is a direct subclass of Graphics.
• Your paint(Graphics g) and paintComponent(Graphics
  g) are called with a Graphics2D object.
• Hence, it is convenient to typecast g to a
  Graphics2D object early in your method
• Graphics2D g2 (Graphics2D)g
• That allows you to call Graphics2D methods when
  you need them.

8
Important Graphics2D Attributes

• Foreground colorsuperseded by fill style
  attribute and Paint interface.
• Clipping regiona Shape, not restricted to
  rectangles.
• Line stylea Stroke. Allows you to control line
  attributes.
• Fill stylea Paint object. A Color, TexturePaint,
  or GradientPaint
• Compositingcombines pixel colours
• Transformcoordinate system (defined by
  translate(), scale(), rotate(), and shear()
  methods)
• Hintsantialiasing and other preferences

9
Important Graphics2D Methods

• draw()outlines an arbitrary Shape
• fill()fills an arbitrary Shape
• hit()detects whether a rectangle intersects an
  arbitrary Shape
• drawString()
• drawGlyphVector()
• drawImage(), drawRenderableImage(),
  drawRenderedImage()

10
The Paint Interface

• Any of the following
• A Color (solid colour)
• A TexturePaint (a tiled image)
• A GradientPaint (a colour gradient)
• TexturePaint and GradientPaint objects are
  immutable.

11
The Shape Interface

• A shape
• Does not have to enclose an area. Can represent a
  path.
• Fundamental Shape-related methods in Graphics2D
• draw()
• fill()
• clip()
• hit()

12
Shape Implementations

• Rectangle (three)
• Round rectangle (two)
• Ellipse/circle (two)
• Polygon
• Line segment (two)
• Arc (ellipse segment, two kinds)
• Bezier curve (four)

13
Stroke

• Describes the pen or brush used to draw.
• BasicStroke is usually suitable
• Lots of details.

14
Fonts and Text

• You can add fonts to the standard ones.
• Provides a method to load a TrueType font by
  name.
• Test for the existence of the font before you try
  to load it.
• You can define attributes for the font and
  transform it.
• You can also provide rendering hints.
• You can define text strings as GlyphVectors that
  can be drawn repeatedly.

15
BufferedImage

• A subclass of Image.
• Represents image data in memory (an Image is data
  being transferred over a network).
• Image processing of a BufferedImage is powerful
  and sophisticated.
• In Swing applications, load an image as an
  ImageIcon.
• Image theImage new javax.swing.ImageIcon(theFil
  eName).getImage()

16
Sample Code

• private BufferedImage the32x32png
• File the32x32File new File("32x32.png")
• the32x32png ImageIO.read(the32x32File)
• ImageIcon the32Symbol new ImageIcon(((BufferedI
  mage)the32x32png).getSubimage(32,0,32,32))

17
More on BufferedImage

• To create an empty one, call createImage() on a
  component. Cast the returned object as a
  BufferedImage
• Use createGraphics() on it to get a Graphics2D
  object.
• Use the Graphics2D object to draw data from an
  Image into the BufferedImage
• Use the com.sun.image.codec.jpeg package for
  reading jpeg data into a BufferedImage and for
  encoding a BufferedImage as a jpeg.

18
Image Processing

• BufferedImage supports image processing. Use the
  filter() method.
• Look at the java.awt.image package.
• Operations supported include
• Arbitrary geometric transformations
• Colour conversions
• Convolution
• Lookup table operations in colour space
• Rescaling in colour space

19
Animation

• Use a background thread to drive the animation.
• To avoid flickering, use double buffering.
• Draw the next frame off-screen, then
• Copy the frame onto the screen all at once.
• Try to avoid redrawing the entire frame, too.
• Note, swing does this automatically.

20
Example Code

• Java Examples in a Nutshell, chapter 12, example
  19