Baklava

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Baklava
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Baklava

• Baklava is a free Sprite Animation Toolkit
• Source code and documentation are included
• There are quite a lot of methods, but it's easier
  to learn them than to write them all yourself
• Baklava uses Java 1.0
• Baklava appears to support only Applets
• http//www.boutell.com/baklava/

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Baklava concepts

• Baklava has Sprites and a Playfield
• Any visible object that has a behavior (moves,
  interacts with other objects) should be a Sprite
• Baklava Sprites have useful predefined behaviors
• holding and displaying an image
• movement, and collisions
• detecting mouse clicks, etc.
• ...but you still probably need to extend the
  Sprite class
• The Playfield is just a container for Sprites

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Backgrounds

• A background is just an image
• Backgrounds typically have no behavior
• Even a moving background doesn't do anything
• In side-scrolling games with ledges, etc., the
  ledges are Sprites the rest may or may not be
• In Baklava, a background is a kind of Sprite

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Importing Baklava

• Download the Baklava classes
• There are only five Sprite, Playfield, Timer,
  GlobalTimerObserver, and FastVector
• Make sure these are in a folder named baklava
• Put the folder as a subfolder of your working
  folder
• If you put the baklava folder somewhere else, add
  it to your CLASSPATH
• Add import baklava. to your program

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Directory structure

• myWorkingDirectory
• myProgram.java
• myProgram.class
• myHero.gif
• myMonster.gif
• baklava (folder)
• Sprite.class
• Playfield.class
• etc.

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How to use Baklava

• import baklava.
• Create a Playfield
• Create some Sprites
• Sprites must be created in a Playfield
• Tell the Sprites what to do
• There are many properties you can set
• For additional behaviors, extend the Sprite class
• Start and display the Playfield

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Create a Playfield

• Playfield p
• p new Playfield(this,
  getBounds().width,
  getBounds().height)
• this the Applet itself
• getBounds() returns the size of the Applet
• For simple Applets, use setLayout(null)

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Create some Sprites

• Sprite s new Sprite(p)
• p the Playground
• Sprite ss new SpritenSpritesfor (int i
  0 i lt nSprites i) ssi new Sprite(p)
• Creating a background Sprite
• Sprite background new Sprite(p)background.setB
  ackground(true)

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Attaching images to Sprites

• First, find out where the Applet is
• base getCodeBase().toString()
• Next, load the image from the same place
• Image image p.getImage(base "/image.jpg")
• Finally, attach the image to the Sprite
• s.setImage(image)
• You can also
• Load from an images subdirectory
• Combine the loading and attaching steps

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Telling Sprites how to move

• sprite.setDirection(degrees)

• sprite.setSpeed(pixelsPerSecond)

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Sprite behavior at edges

• sprite.setEdgeHandling(action)
• tells the Sprite what to do when it hits the edge
• action is one of
• Sprite.edgeSolid -- just stop moving
• Sprite.edgeBounce -- bounce off edge
• Sprite.edgeWrap -- go off and reappear on other
  side

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Telling Sprites where to go

• sprite.setDirectionToward(int x, int y)
• sprite.setDirectionToward(anotherSprite)
• sprite.setTarget(int x, int y)
• Sprite automatically stops moving when it
  arrives, and calls the next method
• sprite.onArrival( )
• This method does nothing (override it)

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Z-order

• Sprites have a Z position as well as X and Y
• Larger Z values are "in front," closer to the
  user
• sprite.setLevel(int level)
• Sprites are created at level 0
• A background should be set to level -1
• Sprites at different levels can still collide

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Collisions

• Baklava detects collisions between Sprites...
• ...but it doesn't do anything about collisions
• To do something when there is a collision
• Create a subclass of Sprite
• Override public void collisionWith(Sprite other)
• Each Sprite will get a collisionWith message
• If they interpenetrate, they will get multiple
  messages

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What did I just hit?

• Java has a class named Class
• object.getClass( ) returns the Class to which the
  object belongs
• Class.forName(String className) returns the Class
  with the given name
• Class objects can be compared with
• Example
• public void collisionWith(Sprite other) if
  (other.getClass() this.getClass()) ...

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Using a timer

• You can set a "timer" on a Sprite
• sprite.setTimer(int milliseconds, int id)
• To react to the timer, override timer(int id)
• public void timer(int id) switch(id) ....
• You can set a timer that notifies every Sprite
• public void setTimerAll(int delay, int timerId)
• There are also "global" timers to send timer
  events to the Applet itself

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Responding to keypresses

• Keyboard and mouse handling is Java 1.0
• I hope to be able to do something about that
• Meanwhile,
• public void keyDown(Event evt, int key)
  if (((char) key) ' ') ...
• Every Sprite will receive this message

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Responding to mouse clicks

• void mouseDown(Event evt, int x, int y)
• void mouseUp(Event evt, int x, int y)
• void mouseMove(Event evt, int x, int y)
• void mouseDrag(Event evt, int x, int y)
• void mouseEnter(Event evt, int x, int y)
• void mouseExit(Event evt, int x, int y)
• Playfield.mouseDrag( ) erroneously calls
  Sprite.mouseMove( ) instead of Sprite.mouseDrag( )

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Dragging a Sprite

• To drag a Sprite
• On mouseDown( ), save old speed and set speed to
  0
• For each mouseMove( ) event, adjust Sprite x and
  y
• On mouseUp( ), restore speed (if desired)
• Adjusting the Sprite's x and y
• public void mouseMove(Event event, int x, int
  y) if (beingDragged)
  setX(getX() x - oldMouseX)
  setY(getY() y - oldMouseY)

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Problems with dragging

• The Java 1.0 event model isn't very good
• Playfield.mouseDrag( ) erroneously calls
  Sprite.mouseMove( ) instead of Sprite.mouseDrag(
  )
• If you move too fast you can "drop" the Sprite
• These problems can be fixed, with some effort
• Baklava still seems a good starting point

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The End