Machine Problem 5: Network Tag

Introduction

A screen shot of an actual game is shown below:

We each represent ourself in the game with our unique bitmapped image. When we enter the game, we transmit our 32x32, 16-color, BMP image to everyone else in the game within a HELLO message. Upon receiving a HELLO message, other players store our image into a local variable on their machine called ImageArray and note that we are active by updating a flag in the Player variable. Once every two seconds, we retransmit our HELLO message to reach new players that may have just entered the game.

The position of the mouse will be used to determine the position of our image on the screen. Over the network, we will transmit our position in an UPDATE message to the other players in the game.

We learn of the positions of other players by listening to the network. We store information from other players in our local Player variable. Positions are specified as an offset on a mode-13 VGA screen. Our movements are limited to within the perimeter of the 320x200-pixel screen.

Program Operation

When the game first begins, one player may become it by pressing the left mouse button. For the rest of the game, It is transferred by contact with another player. when we become it, we cannot tag back the player that just touched us (i.e., no tag-backs). Pressing the right mouse is a cheat buttom that releases it.

We can leave the game at any time by pressing both the left and right mouse buttons at the same time. Just before we exit, we send a GOODBYE message to the other players in the game to let them know we are no longer active in the game.

Run the program in the lab on one or more machines until you understand how it works.

If MP5 doesn't run on your home machine, it is because NetBIOS is not properly installed on your machine. For this MP, it is suggested that you work in the lab.

Network Protocol

Multicast Datagrams are used to transmit messages among players. All Messages are sent to a NetBIOS group called ECE291MP5 are received by all players in the game. When a player first joins they game, they are given the first available name between ECE291Player00 and ECE291Player63.

To simplify the programming for NetBIOS, you have been given NETLIB.LIB -- a library which provides function calls to send and receive datagrams. The NetLIB library calls are summarized below. Additional documentation about NetBIOS and Lockwood's NetLIB functions can be found on our ECE291 Class Resources Web Page.

NetInit: Initializes Network - Returns: Player num in AL SendPacket: Transmits data in TXBuffer - Inputs: AX = Length NetRelease: Release network resources netpost : Procedure called when datagram arrives. Called with AX = Length, BX = Pointer to RXBuffer Must preserve all registers modified Ends with RET (not IRET) TXBuffer: Transmit Buffer (1024 bytes) - Write your data here RXBuffer: Receive Buffer (1024 bytes) - Read from here !

Important Variables

• Player: 64-element array of PlayerType.
  Stores position and status of remote users.
  Modified when packets arrive and used to redraw the screen.
• ImageArray: 64-element array of 1024-byte, uncompressed images.
  Holds local copy of remote user images.
• MyNum: My player number (as determined by NetINIT)
• ItNum: The number of the player that I think is it.
• TagNum: The number of the player that tagged me
• MyPosition: My location on the screen (an from the top-left offset)

Problem Assignment

You may cut & paste your graphic routines from MP4 into MP5.ASM. Edit MP5.ASM to add your new procedures for mouse control, data reception, and updating the screen.

Network, Mouse, and Screen Routines

• All routines should preserve the values of any registers modified
• Use proper segments where needed

• MouseMove
  • Purpose: Position self on the screen at the location of the mouse
  • Variables Updated
    • MyPosition: Sets MyPosition to correspond to mouse location
      
      • Recall that MyPosition is specified to be the screen offset for the top-left corner of MyImage.
      • Limit the range of MyPosition to prevent drawing MyImage to the extreme right or extreme bottom of the the screen.
    • ItNum/TagNum: Set ItNum=MyNum and TagNum=63 if left button pressed
      (allow me to become it)
    • ItNum/TagNum: Set ItNum=63 if right button pressed
      (force self to not be it)
    • ExitFlag: Set ExitFlag=1 if right mouse button pressed
      (allow program to exit)
  • Hints
    • MouseMove can poll the mouse position using an Int 33h routine.
    • Recall that mouse positions range over X=(0..639) and Y=(0..199).
    • Note that MyPosition is based on a screen resolution of 320x200.

• ReDrawScreen
  • Purpose: Redraw the screen with up to 63 players
  • Array Variable Used: Player
  • Output: Writes directly to screen
  • Calls Functions: DrawBox, DrawEmptyBox, DrawBMP
  • Description: Redraw each ACTIVE player on the screen at their current position.
    Outline the player with an empty box when they are it.
    If a player is DEPARTING, remove their image and set their staus to INACTIVE.

• NetPost
  • Purpose: Process Incoming Datagrams
  • Array Variables Modified: Player
  • Output registers: None! (processed within an interrupt)
  • Calls Functions: StoreBMP
  • Description: The NetPost function is called by NetLIB whenever a datagram arrives. The actions taken depend on the message type.
    • HELLO: Set the player status to active and store their image to the array.
    • UPDATE:
      • Update the player's current position.
        
      • If some other player is it AND that player overlapping me AND that player wasn't tagged by me, then I should become it. (ItNum=MyNum, TagNum=PlayerNum).
        
      • If some other player is it AND that player is NOT overlapping me then let him/her become it (ItNum=PlayerNum).
        
      • If some other player is it AND that player was tagged by me, let him/her continue to be it then let him/her become it (ItNum=PlayerNum).
        
    • GOODBYE: Set the player status to departing. Let the ReDrawScreen take care of removing the user from the screen.
  • Hints:
    • You will receive messages from yourself!

Points

• MouseMove: 15 pts
• ReDrawScreen: 15 pts
• NetPost: 20 pts

Preliminary Procedure

1. Obtain the MP5 files by downloading them from the web as mp5.zip or copying them from the netork drive with the following command:
   xcopy /s V:\ECE291\MP5\ W:\MP5
   
2. Copy the 'myimage.bmp' you created for MP4 into your MP5 directory:
   copy W:MP4\MyImage.bmp W:\MP5
3. Run the code in the lab to understand how it works. Experiment with the operation of the left mouse button, the right mouse button, and pressing both the left and right mouse buttons together.
4. Read the existing code given in MP5.ASM. Be sure that you understand the program framework before you write the individual routines.

MP5.ASM