CS4812: Java Lecture IX

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CS4812 JavaLecture IX

• A Stay of Execution
• or
• The Broken Shaft

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(Course Administration Note)

• So far, students have completed
• An aggressive P1, which required code above and
  beyond simple IO handling
• A difficult P2, which covered numerous detailed
  topics
• Event Handling
• Graphics
• GUI design/layout
• Innovative subclass
• Delays in the quarter make it unreasonable to
  assign a complete p3 on the eve of dead week.

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(Course Administration Note)

• Options
• Skip p3 altogether, thereby rendering our
  discussion of graphics/buffering quite irrelevant
  to your CS4812 experience.
• Assign p3, and curve it. (Read shaft.)
• Rework p3 into a pass/fail lab with explicit
  steps, thereby giving exposure to lightweight
  components, etc.
• Lessons Learned
• Student Grading A good thing.
• Its only 2 credits
• Students learn better if the material, and not
  the grade, is made the focus of the course.

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Implementing a double-buffered light-weight
container in Java (JDK 1.1.x)

• Thus far, we have considered
• Problems associated with heavy-weight components.
  (Solution light-weights!)
• Problems associated with animation. (Solution
  double buffering/clipping areas)
• The lab (read final) version of p3 will
  require the combination of these techniques.
• Today, we cover some specific problems associated
  with images and image loading

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Images Why?

• Our light weights all have a paint() method
  useful for describing the look and feel of our
  component.
• To make full use of the paint() method, we have
  to become familiar with image manipulation in
  Java.

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Images What?

• The AWT provides the java.awt.Image class.
  Images are handed off to other components for
  drawing.
• For example, you never have an image draw itself
  rather, an image reference is drawn used by a
  graphics object
• g.drawImage(Image, int, int, ImageObserver)

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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()

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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 peformed by the image package.
  Most of the methods you will use are found in the
  Image class.

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Image Producers/Consumers

• Image production is decided 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.

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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

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Loading images

• Images are first obtained from the toolkit. An
  applet has a toolkit with factor 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)

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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)

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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

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ImageObserver Constants

• Other constant 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

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• 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(500)
• //catch(Exception e)
• return true

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Fun with Image Filters

• The use of image filters allows us to crop images
  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!

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Other image filters Memory-sourced images

• 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)

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Pixel-Grabbing

• A complement to memory image sourcing is grabbing
  an images 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.