Final Project: Zelda 291: Input

Introduction

Zelda 291 will accept information from both the keyboard and either a joystick or gamepad.

Problem Description

This part of the program is fairly straightfoward. It basically just uses a common keyboard interrupt and a standard joystick function. If two direction keys are pressed, the program will move in one direction and must "remember" the other direction in case the player releases the other key. A new aspect of this that was not done in the machine problems is that we will use press and release interrupts for the keyboard.

I also worked on various introduction screens. Perhaps the most difficult part of this was implementing a scrolling feature. It was also a challenge to display the scrolling file since it was 800 lines long and only 200 can be on the screen at once.

Keyboard

The gaming controls on the keyboard will be functional only when the joystick is on. The control keys will always be functional. The keyboard will accept the following commands:

• Arrow Keys -- Movement (Cardinal Directions)
• Alt -- Primary Attack
• Space Bar -- Pause
• J -- Toggle Joystick On/Off
• Esc -- Exit the Game

Joystick/GamePad

The joystick will only become functional if the user presses the Y key at the intial screen. Some joysticks contain only two buttons (A and B). However, the Gravis Gamepad contains four buttons, two of which will be used. It will accept the following inputs:

• D-pad or Joystick -- Movement (Cardinal Directions)
• Button A -- Primary Attack
• Button D -- Pause

Scrolling

The scrolling was implemented by first loading the screen with the first 64000 bytes of the uncompressed file. Then, to implement scrolling, each line on the screen was shifted up one row, and the last row was filled with the next block of data from the file.

Procedures

• InputInstKbdInt
• • Purpose: Installs InputNewKbdInt as the new interrupt
  • Inputs: None
  • Outputs: Stores old interrupt in OldKIVector
• InputDeInstKbdInt
• • Purpose: OldKIVector is installed as the interrupt
  • Inputs: None
  • Outputs: None
• InputNewKbdInt
• • Purpose: The keyboard interrupt used for the game
  • Inputs: None
  • Outputs: Writes InputAction, InputX_Direction and InputY_Direction
• InputGetJstkInfo
  • Purpose: Polls the joystick for x,y values and gets the buttons pressed
  • Inputs: Joystick input
  • Outputs: Writes Action, X_Direction and Y_Direction
• InputJstkCalib
• • Purpose: Calibrates the joystick
  • Inputs: None
  • Outputs: Writes Xmin, Xmax, Ymin, Ymax
  • Notes:
  • • First, an inital screen is shown asking the user to choose joystick input.
    • Then, if Y is pressed, another screen appears, instructing the user.
    • The user holds direction in upper left position and presses button A.
    • Then, another screen appears, instructing the user.
    • The user holds direction in lower right position and presses button A.
    • If 'N' is pressed at title screen, the function skips to normal gameplay.
    • The function calculates an automatic 12.5% tolerance on all the inputs.
• DisplayStory
  • Purpose: Displays the initial scrolling screen
  • Inputs: None
  • Outputs: Writes to screen
• GetPallette
  • Purpose: Gets the pallette from the file pallette.pcx. Used because the pallette must be set before the scrolling screen begins.
  • Inputs: None
  • Outputs: Writes to Screen
• LoadPCX
  • Taken directly from my mp4. It worked then, why won't it work now.