Part IV: Chapter 3

1
Part IV Chapter 3

• Debugging
• Alert
• Connections
• Resources
• Game Graphics
• Media

2
Debugging

• While programming in WTK, you can use
  System.out.println() method for debugging your
  program.
• In an emulator, System.out.println() usually
  outputs to the emulator console or log. In a real
  device, it may just get junked. However, some
  devices echo standard output and standard error
  to their serial ports, so if you plug in a
  terminal or terminal emulator, you might be able
  to see the output.

3
Alert

• An alert dialog is a term for a particular type
  of dialog box that occurs in a graphical user
  interface. It is also known as an alert box,
  alert window, or alert popup.
• Alerts were designed for two main uses. The first
  is to inform the user than an operation could not
  continue or complete due to some insurmountable
  error. The second is to warn them that the
  current course of action could be in some way
  dangerous or detrimental, and to offer the option
  of not proceeding.

4
Alert

• private Alert alert
• ...
• alert new Alert("Busy", "Please try again.",
  null, AlertType.WARNING)
• alert.setTimeout(Alert.FOREVER)
• display.setCurrent(alert, form)

5
Socket Connection

• Sockets are used for sending and receiving
  information over the network (WAP, OTA, etc.)
• The creation of Connections is performed
  dynamically by looking up a protocol
  implementation class whose name is formed from
  the platform name (read from a system property)
  and the protocol name of the requested
  connection(extracted from the parameter string
  supplied by the application programmer.)
• The parameter string that describes the target
  should conform to the URL format as described in
  RFC 2396.
• This takes the general form
• schemetargetparms
• where scheme is the name of a protocol such as
  http.
• The target is normally some kind of network
  address.
• Any parms are formed as a series of equates of
  the form xy. Example typea

6
Socket Connection example

• InputStream is
• OutputStream os
• SocketConnection sc
• Sender sender
• ...
• try
• sc (SocketConnection) Connector.open("socket//l
  ocalhost5000")
• si.setText("Connected to server")
• is sc.openInputStream()
• os sc.openOutputStream()
• while (true) // Loop forever, receiving data
• StringBuffer sb new StringBuffer()
• int c 0
• while (((c is.read()) ! '\n') (c ! -1))
• sb.append((char) c)
• if (c -1) break
• catch (ConnectionNotFoundException cnfe)

7
Server Socket

• SocketConnection sc
• ServerSocketConnection scn
• ...
• scn (ServerSocketConnection) Connector.open("soc
  ket//5000")
• // Wait for a connection.
• ...
• sc (SocketConnection) scn.acceptAndOpen()

8
HTTPConnection

• Using HHTP connection instead of a stream socket.
  This code looks very similar to the socket code,
  but there is a striking difference. The socket
  code first opened an OutputStream and sent the
  request to the web server before trying to read
  the response.
• HttpConnection conn
• InputStream is
• ...
• String url "http//java.sun.com/"
• conn (HttpConnection)Connector.open(url,
  Connector.READ_WRITE)
• if (conn.getResponseCode( ) HttpConnection.HTTP
  _OK)
• is conn.openInputStream( )
• final int MAX_LENGTH 128
• byte buf new byteMAX_LENGTH
• int total 0
• while (total lt MAX_LENGTH)
• int count is.read(buf, total, MAX_LENGTH -
  total)
• if (count lt 0) break
• total count
• is.close( )

9
Image from HTTP

• You can also use HTTPConnection for downloading
  images to the device
• HttpConnection conn
• InputStream is
• ...
• ...
• is conn.openInputStream()
• Image NewImage Image.createImage(is)

10
Resources

• Application resource files are accessed
  usinggetResourceAsStream(String name) in
  java.lang.Class.
• In the MIDP specification, getResourceAsStream is
  used to allow resource files to be retrieved from
  the MIDlet Suites JAR file.
• Resource names refer to the contents of the
  MIDlet suite JAR file. Absolute pathnames,
  beginning with / are fully qualified file names
  within the jar file.

11
Resources

• InputStream is null
• try
• is getClass().getResourceAsStream(
• "/level1.dat")
• if (is ! null)
• while ((c is.read()) ! -1)
• ... // Process input
• is.close()
• catch (java.io.IOException ex)
• ...

12
GameCanvas

• The GameCanvas class provides the basis for a
  game user interface. In addition to the features
  inherited from Canvas (commands, input
  events,etc.) it also provides game-specific
  capabilities such as an off-screen graphics
  buffer and the ability to query key status.
• A dedicated buffer is created for each GameCanvas
  instance. Since a unique buffer is provided for
  each GameCanvas instance, it is preferable to
  re-use a single GameCanvas instance in the
  interests of minimizing heap usage.

13
Layer

• A Layer is an abstract class representing a
  visual element of a game. Each Layer has position
  (in terms of the upper-left corner of its visual
  bounds), width, height, and can be made visible
  or invisible. Layer subclasses must implement a
  paint(Graphics) method so that they can be
  rendered.
• The Layers (x,y) position is always interpreted
  relative to the coordinate system of the Graphics
  object that is passed to the Layers paint()
  method.

14
Sprite

• A Sprite is a basic visual element that can be
  rendered with one of several frames stored in an
  Image.
• Different frames can be shown to animate the
  Sprite.
• Several transforms such as flipping and rotation
  can also be applied to a Sprite to further vary
  its appearance. As with all Layer subclasses, a
  Sprites location can be changed and it can also
  be made visible or invisible.

15
Sprite Frames

• The raw frames used to render a Sprite are
  provided in a single Image object, which may be
  mutable or immutable.
• If more than one frame is used, the Image is
  broken up into a series of equally-sized frames
  of a specified width and height.
• The same set of frames may be stored in several
  different arrangements.
• The developer must manually switch the current
  frame in the frame sequence. This may be
  accomplished by calling setFrame(int),
  prevFrame(), or nextFrame() methods.
• private Sprite createBody() throws IOException
• Image image Image.createImage("/body.png")
• return new Sprite(image, 27, 32)

16
LayerManager

• The LayerManager manages a series of Layers. The
  LayerManager simplifies the process of rendering
  the Layers that have been added to it by
  automatically rendering the correct regions of
  each Layer in thea ppropriate order.
• The Layer Manager maintains an ordered list to
  which Layers can be appended, inserted and
  removed.A Layers index correlates to its
  z-order the layer at index 0 is closest to the
  user while the Layer with the highest index is
  furthest away from the user.

17
LayerManager

• The indices are always contiguous that is, if a
  Layer is removed, the indices of subsequent
  Layers will be adjusted to maintain continuity.
• private LayerManager mLayerManager
• ...
• mLayerManager.append(Sprite1)
• mLayerManager.append(TiledLayer)
• mLayerManager.setViewWindow(0, 0, screenWidth,
  screenHeight)
• ...
• mLayerManager.paint(g, 0, 0)

18
TiledLayer

• The TiledLayer is a little like Sprite but it is
  mainly meant for backgrounds, roads or other
  larger areas. TiledLayer consists of a grid of
  cells, which can be filled with images or
  tiles.This can be used by game developers for
  developing tiled layers in their aplications.
• A TiledLayer can be rendered by manually calling
  its paint method it can also be rendered
  automatically using a LayerManager object.

19
TiledLayer

• TiledLayer tiledLayer
• Image bg
• int tileData8,8,8,9,9,8,8,8,8,8,8,14,8,8,8,8
  ,10,10,10,
• 10,10,8,8,14,8,8,10,10,10,10,10,8,8,8,8,10,9,10,9,
  10,
• 8,8,14,8,8,8,8,14,8,8,8,8,8,8,8,8,10,8,10,9,9,
• 8,8,9,9,8,8,9,11,11
• ...
• try
• bgImage.createImage("/bg.png")
• catch(Exception e)
• tiledLayernew TiledLayer(tileData0.length,
• tileData.length, bg, 30, 30)
• //Set the tile data
• for(int i0iltset.lengthi)
• for(int j0jlttileData0.lengthj)
• tiledLayer.setCell(j,i, setij)

20
Media Playback

• javax.microedition.media package is introduced in
  MIDP2.0 profile.
• This package supports sound and upward
  compatibility with MultiMedia API.It has Manager,
  Player and Control as main objects.
• Different audio files, from various locations can
  be played on mobile.

21
Simple Media Playback

• try
• Player p Manager.createPlayer(
• "http//webserver/music.wav")
• p.start()
• catch (IOException ioe)
• catch (MediaException me)

22
Playing Back from Media Stored in JAR

• try
• InputStream is getClass().getResourceAsStream("m
  usic.wav")
• Player p Manager.createPlayer(is,
  "audio/X-wav")
• p.start()
• catch (IOException ioe)
• catch (MediaException me)