Final Project by Boris Klaydman

CS306

Processing Systems and Structures

B. Klaydman

Final Project
Word School

Updated on 4-20-2002

Updated again on 4-21-2002

Team members:

Project leader and programmer: Boris Klaydman.

This is a single user project and was implemented solely by me. This implementation includes:

Displaying of images on the screen
Reading and processing user input
Logic and interrupt handing
Responsibilities also included graphic files and user interface design

Introduction

This project is an Assembler implementation of educational game for pre-school age children. When player loads the game he or she is presented with a random picture that represents a word. The child has three attempts to guess the correct letter. Each time the child presses a letter it is graphically displayed on the screen with a corresponding message letting him/her know if the guess was right. If the number of guesses exceeds three or child guesses correctly the new image loaded and the game starts over.

Problem Description:

The most challenging aspect of the project is the time frame (only a week left with 3 other labs due on the same week) and total isolation (working on the project alone). The project is designed to as practice of displaying graphic image files on the screen using assembler. The PCX format was chosen as primary graphic format of images that the user interface is composed of. In the project the programmer has to deal with processing of the user input, refreshing small positions of the screen, randomly selecting objects for displaying. The scope of the problem is limited, but it extendable. Other options may include use of sound, transitions between images, and creating different modes of the game. For example, the game can be changed with some effort to a math game, where the user has to guess the result of the simple calculations, but this option requires a team of at least 2 people to be done in time.

Implementation:

Since the main focus of the problem is loading and displaying of the PCX files and the target to the game is letter recognition, there will be two main byte sizes arrays that hold the names of the files to process. The names of the files are null terminated and contain only 8 characters for easy access using the shift operation (SHL BX, 3 multiplies by 8). Array of picture files: Pict db 'p00.pcx', 0 db 'p01.pcx', 0 db 'p02.pcx', 0 db ............ db 'p26.pcx', 0 Array of letter files: Lett db 'L00.pcx', 0 db 'L01.pcx', 0 db 'L02.pcx', 0 db ............ db 'L26.pcx', 0 ; Holds array of picture that represent answers to a question Ansr db 'an0.pcx', 0 db 'an1.pcx', 0 db 'an2.pcx', 0 db 'an3.pcx', 0 ; Holds array of picture that represent guess number Tryn db 'tr0.pcx', 0 db 'tr1.pcx', 0 db 'tr2.pcx', 0 db 'tr3.pcx', 0 Screen db 'screen.pcx', 0 ; The main screen The main procedure loops until user presses the escape key. During each iteration of the loop the input from the user is processed and the screen is updated accordingly. The main component of the project is the PCX loading routine. This routine loads image files from the disk and displays them starting from position specified by DX. The size of current picture is specified in variables: XSize dw 0 ; Size of currently loaded picture PicStart dw 0 ; End position of current picture on the screen PicEnd dw 0 ; End position of current picture on the screen To clear the parts of the screen the empty images are loaded and displayed in correct places. The whole algorithm of the project is based on splitting the screen into small pieces and loading them in correct places and order.

Additional constants:

; Video Memory Segments (Store in ES) VIDTEXTSEG EQU 0B800h ; Text-mode video VIDGRSEG EQU 0A000h ; Graphics video SCREENSTART EQU 0; Starting position of screen on the screen SCREENEND EQU 320*200; Ending position of screen on the screen SCREENWIDTH EQU 320 ; Width of screen on the screen LETTERSTART EQU 30*320 -187 ; Starting position of letters on the screen LETTEREND EQU 30*320 -187 + 121*320 + 130; Ending position of letters on the screen LETTERWIDTH EQU 130 ; Width of letters on the screen PICTURESTART EQU 37*320 ; Starting position of pictures on the screen PICTUREEND EQU 37*320 + 125*320 + 186; Ending position of pictures on the screen PICTUREWIDTH EQU 186 ; Width of pictures on the screen TRYSTART EQU 175*320 + 80; Starting position of tries on the screen TRYEND EQU 175*320 + 80 + 24*320 + 22; Ending position of tries on the screen TRYWIDTH EQU 22 ; Width of tries picture on the screen ANSSTART EQU 160*320 ; Starting position of answers on the screen ANSEND EQU 160*320 + 40*320 + 200; Ending position of answers on the screen ANSWIDTH EQU 200 ; Width of tries answers on the screen

Procedures:

main

Purpose:
- Process the user input
Input:
- None
Output:
- None
Registers:
- Not relevant
Assumptions:
- Assumes that graphic files are all in the same directory with the program
Notes:
Description:
- This is the main section of the program. It is responsible for processing any keyboard input and calling appropriate routines. First main changes the video mode to graphic mode, then it clears the graphic screen by drawing appropriate pictures in right places. Then a random number in chosen in range 0 to 25 (for representation of the current letter), appropriate picture for the letter is loaded and maximum 3 guesses of the letter allowed by the loop. The main procedure was extended. Now the game has 3 parts. The first one is described above. The second part of the game loads images and corresponding letters so the child can memorize them. The third part lets the child press a letter and shows both the picture and letter that corresponds to this picture.

clearScreen

Purpose:
- Writes the default content on the screen
Input:
- None
Output:
- Writes to graphic screen
Registers:
- All modified preserved
Assumptions:
- Assumes that graphic files are all in the same directory with the program
Notes:
Description:
- The procedure sets DX to point to the correct name for default pictures, set their sizes and correct locations and repeatedly calls the DisplayPicture to clear the screen.

displayPicture

Purpose:
- Loads and displays a PCX file of specified size starting from specified location
Input:
- [PicEnd] - has ending point on the screen
- [PicStart] - has starting point on the screen
- [XSize] - has the width of the picture
- DX - First byte of the of the name of the file to load
Output:
- Writes to PCX image on the screen
Registers:
- All modified preserved
Assumptions:
- Picture must be in the same directory with the program
Notes:
- Handles the file read errors, but in that case no image is displayed
Description:
- The header of the PCX file is skippedand and each pixel on the screen set accordingly, which draws the picture on the screen. The supplied size of the picture used for correct pixel placement.

randomNum

Purpose:
- Generate a random number in range 1 to 26 for file section
Input:
- None
Output:
- BX - contains value 1 to 26
Registers:
- All modified preserved
Assumptions:
Notes:
Description:
- Sets BX to a value between 1 and 26 for correct file access operation by using the IN command from prot 40h and manipulating the result.

showLetter

Purpose:
- Shows user entered letter on the screen
Input:
- BX - contains a index (between 0 and 26) of selected letter
Output:
- Writes to graphic screen
Registers:
- All modified preserved
Assumptions:
Notes:
- When BX = 0 the letter is replaced with default question mark
Description:
- Set DX and picture dimentions according to the value in BX for displaying correct picture in correct place and calls the displayPicture that does the work.

showPicture

Purpose:
- Shows user a picture that represents a letter on the screen
Input:
- BX - contains a index (between 0 and 26) of selected letter
Output:
- Writes to graphic screen
Registers:
- All modified preserved
Assumptions:
Notes:
- When BX = 0 the picture is deleted by drawing an empty picture on the screen
Description:
- Set DX and picture dimentions according to the value in BX for displaying correct picture in correct place and calls the displayPicture that does the work.

showGuessNum

Purpose:
- Shows guess number on the screen
Input:
- AL - contains code of the guess number (0 - clear, 1 - try #1, 2 - try #2 , 3 - try #3)
Output:
- Writes to graphic screen
Registers:
- All modified preserved
Assumptions:
Notes:
Description:
- Set DX and picture dimentions according to the value in AL for displaying correct picture (Guess number) in correct place and calls the DisplayPicture that does the work.

showGuess

Purpose:
- Shows responce to a guess - correct or incorrect
Input:
- AL - contains code of the guess (0 - clear, 1 - try again, 2 - correct , 3 - wrong)
Output:
- Writes to graphic screen
Registers:
- All modified preserved
Assumptions:
Notes:
Description:
- Set DX and picture dimentions according to the value in AL for displaying correct picture (Guess-related message) in correct place and calls the DisplayPicture that does the work.

External Routines:

In the project some of the library functions from MP5 are used:

The kbdin is used to process the input
dosxit to exit the program
showPCX Found this code on the internet and converted it to a SetPallet procedure that is called only once in the beginning of the program to set the pallet. The code for actual drawing of the pictures on the screen is my and it is original. The modifications were done on 4-21-2002 after my procedure was complete. Thanks to Eric Meidel, Nathan Jachimiec, and Peter Johnson for modifing the MASM code that they also found on the net and making it possible for me to use as setPallet procedure in my program.

Final Project Word School