CS 4812: Java

1
CS 4812 Java
xemacs

• Lecture VI
• A Few Notes on Being
• Productive In Java

2
Administrative Announcement

• Effective for p3, a new augmentative grading
  system will be used.
• If you turn in a solid draft of your program by
  the 19th, you get X points added to your final
  grade for p3.
• The exact value of the additional points will be
  (100 - the lowest grade for p2.) Details to
  follow.
• So, by starting early, you pick up some insurance.

3
Image Production and Consumption in Java

• Many of the lightweights created in p2 used
  images, which relied on the paint() method to
  render the component.
• Some of you experienced delays in loading the
  images, or in getting the images to appear.
• To make full use of the paint() method, we have
  to become familiar with image manipulation in
  Java.

4
Images What?

• To allow for image manipulation, the AWT provides
  the java.awt.Image class. Images dont draw
  themselves. Instead, Images are handed off to
  other components for drawing.
• For example, you cant have an Image invoke
  drawImage on itself instead, an Image
  reference is used by a graphics object
• g.drawImage(Image, int, int, ImageObserver)

5
java.awt.Image

• public abstract int getWidth(ImageObserver)
• public abstract int getHeight(ImageObserver)
• public abstract ImageProducer getSource()
• public abstract Graphics getGraphics()
• public abstract Object getProperty (String name,
  ImageObserver)
• public abstract void flush()
• getScaledInstance(int, int, int)

6
Field Indices for hints argument to
getScaledInstance(int, int, int)

• java.awt.Image.SCALE_AREA_AVERAGING
• Use the Area Averaging image scaling algorithm.
• java.awt.Image.SCALE_DEFAULT
• Use the default image scaling algorithm.
• java.awt.Image.SCALE_FAST
• Choose an image scaling algorithm that gives
  higher priority to scaling speed than smoothness
  of the scaled image.
• java.awt.Image.SCALE_REPLICATE
• Use the ReplicateScaleFilter image scaling
  algorithm.
• java.awt.Image.SCALE_SMOOTH
• Choose an image scaling algorithm that gives
  higher priority to image smoothness than scaling
  speed.

7
The image Package

• Most of the code for manipulating images resides
  not in the Image class, but in the java.awt.image
  package.
• The heavy-lifting associated with Image
  production is performed by the Image package.
  Most of the useful methods are found in the Image
  class.

8
Image Producers/Consumers

• Image production is decidedly async in Java.
• Java handles Image production with the
  java.awt.image.ImageProducer class.
• The producer creates the bits making up an Image
  , and updates the Image as it loads.
• The java.awt.image.ImageConsumer interface has
  but a single method
• imageUpdate()
• The producer calls this method to report updates
  in the progress of an Image .

9
Image Consumers

• Just about everything in the AWT is an Image
  consumer, meaning it implements
  java.awt.image.ImageConsumer.
• Component, for example, implements this
  interface, making every widget Image -aware.
  (Light and heavy weights alike!)
• Thus, if a method takes an ImageObserver
  argument, just pass in a component
• g.drawImage(myImage, x, y, myComponet)

10
Loading images

• Image are first obtained from the toolkit. An
  applet has a toolkit with factory settings
  applications need to call the static toolkit
  reference
• APPLET
• Image I getImage(getCodeBase(), sox.gif)
• APPLICATION
• Image I Toolkit.getDefaultToolkit().getImage(get
  CodeBase(), sox.gif)
• (Note getDocumentBase() works as well)

11
Image Observer Methods

• Numerous methods take an Image observer argument
• prepareImage (in Component Toolkit)
• checkImage(in Component Toolkit)
• drawImage (in Graphics)
• getWidth/getHeight(in Image class)

12
Using Image Observers

• Since Image producers call the consumer
  imageUpdate method, we can use this method as a
  means of tracking media loading.
• We can override imageUpdate to wait on any
  repainting until allbits are loaded
• Consider
• public boolean imageUpdate(Image image, int
  flags, int x, int y, int w, int h)
• if (flags ALLBITS) !0) repaint()
• return true

13
ImageObserver Constants

• Other constants defined in ImageObserver include
• ABORT--if aborted loaded
• ALLBITS--if all bits loaded
• ERROR--if error occurs
• FRAMEBITS--another complete frame of a multiframe
  image is now available
• HEIGHT
• PROPERTIES--dimensions are known
• SOMEBITS--more pixels available
• WIDTH

14

• import java.applet.import java.net.URL
• import java.awt.Graphicsimport java.awt.Image
• public class smoothie extends Applet
• Image im
• public void init()
• super.init()
• URL base getCodeBase()
• im getImage(base, "sox.gif")
• public void paint (Graphics g)
• g.drawImage(im, 0,0, this)
• public boolean imageUpdate(Image image, int
  flags,
• int x, int y, int w, int h)
• if ((flags ALLBITS)!0)
• repaint()
• //tryThread.sleep(50)
  catch(Exception e)
• return true

15
Fun with Image Filters

• The use of an ImageFilter allows us to crop an
  Image into smaller Image objects
• Consider
• Image StripImage
• getImage(getCodeBase(), strip.gif)
• ImageFilter f
• new CropImageFilter (x, y, w, h)
• ImageProducer p new FilteredImageSource(StripI
  mage.getSource(), f)
• Image Im createImage(p)
• Also, look at RGBImageFilter class!

16
Other Image filters Memory-sourced Image

• One can also specify a range of memory (or
  rather, an object) as an Image source
• myInts new intSIZE
• MemoryImageSource m new MemoryImageSource(w,
  h, myInts, start, width)

17
Pixel-Grabbing

• A complement to memory Image sourcing is grabbing
  an Image s pixels and stuffing them into an
  array
• pixels new intwh
• PixelGrabber pig new PixelGrabber (image, x, y,
  w, h, pixels, 0, width)
• trypig.grabPixels()
• catch (InterruptedException e)
• We can use pixel grabbers and memory Image
  sources to manipulate and edit Images on a very
  small level.