Leftover Demos: JPEGEncoder, Animation-demos. Translucency demos.

1
Lecture 8

• Leftover Demos JPEGEncoder, Animation-demos.
  Translucency demos.
• Internationalization, Customization
• Accessibility
• History of Animation/Early Cinema
• Animation how-to
• Example Dungeon Dregs

2
Internationalization

• 2 System properties are typically used to
  customize program interface user.language and
  user.region
• There is a standardized set of 2-letter ISO
  codes for these. Languages en, fr, de, es, sw,
  etc. Regions US, FR, CA, CH, DE, GB, etc.
• Also called Localization

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I18N How-To

1. Subclass ResourceBundle once for every supported
   Locale. All locality-specific resources go in
   here.
2. Load ResourceBundle corresponding to users
   preference.
3. Get all locale-specific Strings and other
   resources from the bundle. Use wherever
   appropriate.

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I18N Demo1 Notes

• Some redundancy is required and desirable.
  MyResources, MyResources_en and MyResources_en_US
  are identical. These provide defaults in case
  not all system properties are set.
• Watch for pitfalls String resources may not be
  the expected size. Meanings may change in subtle
  ways.

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Formats

• To get accents and special characters, need to
  know some Unicode. \u
• NumberFormat, DateFormat.
• Constructing sentences from pieces is not so
  easy anymore. Languages differ in sentence
  structure and ordering.
• Move all sentence-constructing into bundles.
• Use MessageFormat class. Bundle format strings.

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Beyond Strings

• Can customize look and feel for different
  locales. ResourceBundles can contain filenames,
  such as image files, and can even contain
  customized classes such as dialogs or frames.
• ResourceBundles can inherit from one another.
  Might have a single resource file with common
  data for Europe.

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Customization

• User may want to change language preference for
  your program only, or alter other settings from
  the defaults.
• Easy to do for one session. Just modify the
  attributes.
• Would also like preferences to persist from one
  session to another. Need to create a preferences
  file.

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Preferences files

• Location
• Preferred location varies with system. Program
  directory for single-user PCs, user directory for
  multi-user systems.
• Format
• Serialized objects? Easy. Hard to edit.
• Custom format. Must deal with syntax.

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Preferences class

• Define a preferences class along the same lines
  as ResourceBundle. Basically a Map or Hashtable
  of keys and values.
• Write preference file using Serialize or entry
  by entry.
• On startup, load the preferences from the stored
  file. Defaults if this fails.

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What to customize

• A good topic for use case analysis and user
  surveys. What will the product be used for?
  What do users ask for?
• Better to offer users a limited set of
  ready-made preference sets than to make them
  choose everything individually.
• Options to turn features off.

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What not to customize

• Everything. Want to be able to explain to users
  how to do any given task, without having to worry
  about how they customized the application.
• Menus. Makes sense to have all commands
  accessible through menus in fixed locations.
  Customizable toolbars for commonly-used commands.

(This isnt a hard-and-fast rule)
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Accessibility

• Swing components have methods to support
  assistive technologies, which for example may
  allow vocal control and audio display of a GUI
  interface.
• Can play with this download Monkey.
• To take advantage, you need to label components
  with informative text.

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Making components accessible

1. Label all JComponents using setToolTipText(String)
   method. This also serves as help for new users.
2. When JLabels are meant to label something, use
   JLabel.setLabelFor()
3. JComponent.getAccessibleContext().setAccessible()
   where Name or Description.

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History of the Magic Lantern

• Projected Images have been around in one form or
  another since at least 1420.
• By 1700s, used for popular entertainment.
• Special effects such as rear-projection onto a
  translucent screen, projection onto cloud of
  smoke, dissolving views.
• 1895 Cinematographe invented.

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Pre-history of Cinema

• As early as 1674, idea of quick succession of
  glass slides.
• 1832 Fantoscope, Stroboscope. Illusion of
  motion created by persistence
  of vision
• 1870s combined with photography.
• 1890s celluloid film.

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Persistence of Vision

• Images remain on the retina for about 1/14 of a
  second. Small delay between bright images not
  visible.
• Frame rate of 30Hz is generally considered
  flicker-free.
• Typical monitor refresh rate is 70-130Hz. (Hz
  Hertz per second).

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Basic Animation

• Display image sequence at intervals.
• Images must line up exactly
• can detect 1-pixel shift on most monitors
• Intervals must be same length
• movement will appear jerky
• Intervals should be short.
• probably no benefit beyond 1/30 second
• User expectations vary with application

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Corollaries

• Must ensure adequate computational resources.
  Small delays lead to jerks. Example scrolling in
  IE.
• Less computationally demanding to animate small
  images, or simple images such as rectangles
  filled by solid color.
• Rendering text especially slow in Java.

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Simple animation in Swing

• Use javax.swing.Timer to generate ticks every N
  milliseconds.
• On tick, display current frame, then compute
  next frame.
• Order matters computing frame may take variable
  time displaying should not.

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Speed-up tricks downloads

• Downloading slow, and speed varies.
• Track downloads with a MediaTracker. Start
  animations after downloads complete.
• Fewer HTTP connections saves time. Combine
  images into 1 file extract with graphics
  operations. Better still put all images and
  source into a jar file, and extract locally.
• Generate graphics locally if possible.

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Speed-up tricks precompute

• Compute once, draw many times.
• Avoid Graphics.drawString (very slow)
• Precompute GlyphVectors or Images for strings
  which you draw more than once.
• Same for digits of numeric displays.
• Use antialias and transparency effects in
  precomputing. For actual display, just copy in
  the BufferedImage.

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More speed tricks

• Dont repeat graphics ops wastefully
• e.g. Triple buffering (next slide).
• Minimize area to redraw.
• Small rectangles can be updated faster.
• Graphics.setRenderHints(RENDER_SPEED)
• Ask user not to run other jobs.

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Case-study Dungeon Dregs

• About the lamest of many cool games at Jva On
  The Brain by Karl Hörnell.
• In public domain.
• Lots of game applets on the site, together with
  notes about their creation, including design
  choices and implementation details. Go browse
  it!

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Welcome to the Dungeon
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Dungeon Graphics
All the graphics for this game have been stored
in a single .gif file. This is downloaded and
stored as an Image. The individual pieces are
copied out as needed. This method reduces
download time.
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Triple-Buffering

• There are 2 buffers, farBuffer and nearBuffer
  (both class Image).
• farBuffer contains background elements, and is
  changed rarely. (e.g. crate smashed or
  prisoner freed).
• nearBuffer is redrawn frequently, with all the
  moving elements.
• nearBuffer drawn to Panel when done.

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Triple-Buffering
farBuffer static elements
nearBuffer farBuffer mobile elements
screen nearBuffer, but drawn in 1 step.
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Animation Loop

• Since this is an Applet, it uses Thread.sleep
  instead of a Timer.
• Every 85ms, tick occurs. New positions are
  computed, farBuffer and nearBuffer are updated,
  and screen is refreshed.
• Finite state machine is simulated to minimize
  processing time. Slow tasks are spread over
  several ticks.