Programs - Designer

Programmer’s Guide

Game Designer Pack for MS-DOS™

Contents

Introduction

Accessing Source Code

Program Execution

Game Play Unit

Designing Units

Other Units

System Dependence

Introduction

Welcome to the world of Game Designer Pack from Darkskies. This guide outlines the programming techniques used in Game Designer Pack and how they are implemented.

Accessing Source Code

The source code is supplied on a disk labelled ‘Game Designer Pack Source Code’. It is contained in a .zip file. This standard is well known and any unzipper such as PKUNZIP or WinZip will read the file format. The program is arranged into several units. Each unit has its own task which it must perform.

Program Execution

The program starts by running the initialization procedure. It then displays the welcome screen and displays the menu. Nothing more is executed until after the menu and therefore the program is ended and the exit procedure installed during initialization is executed.

This procedure is responsible for setting up everything required for the program to run. It does the following:

  • Scan drives for the I/O unit.
  • Enter graphics mode and set-up colours
  • Initialize mouse, set sensitivity and limits and cursor
  • Installs exit procedure.
  • Allocate memory for data structures

Display the welcome message along with the copyright message on the screen and waits for the user to press a key or button.

The entire menu procedure does very little. It sets up a pointer to a menu structure that is composed of a linked list created by procedures in the menu unit. It then uses the menu unit to display the menu and act on the user’s choice. It then de-allocates the menu structure to save memory and returns to the main program.

Most of the sub-units have complex entry procedure requirements and it is not possible to pass them from the menu unit therefore ‘wrappers’ have been written that will allow the menu to execute the procedures.

The menu options basically are:

  • Play Game
  • Edit Game
    • Edit Sprites
    • Edit Mappings
    • Edit Rooms
    • Edit Plans

On execution the procedure clears up all allocated structures and returns the user to text mode.

Game Play Unit

This unit allows the user navigate around the worlds that have been created, exploring them, collecting the artefacts and fighting monsters.

Obviously more than a single type of game could be played – user must select one to play.

Clears the screen and uses the get file function in the I/O unit to retrieve the name of a game file. This file is then loaded using the load game procedure.

This procedure opens the file whose name is passed as a variable. It then verifies that the file is of the correct format and reads the version number from it. It then reads the relevant information from the file and uses the load plan and load sprite map procedures to further populate the data structures.

Progress Display

  • The routine facilitates the passing through of the pointer to the progress display procedure, which will be discussed later in the plan and sprite maps loading procedures.

Before the game can proceed the user needs to select which icon they will be using as their character.

  • Starts by clearing the screen and setting up text displays.
  • Collect all available player icons and remember what we have.
  • Repeat
    • Check for key presses
    • Act on key pressed
    • Check for mouse movement and if applicable select the icon that the mouse is over.
    • Check for buttons pressed
  • Until selection has been made or play cancelled

This is the entry that allows the user to actually play the game.

  • Check whether the user has selected an icon to play with, if not run the choose player procedure
  • Repeat
    • Check for key presses
    • Act on keys pressed
    • Check for mouse movement
    • Check for buttons pressed and move character to that position
  • Until End of Game
  • Display totals screen

Go

A procedure that is passed a direction and processes that request to find out what the program must do. Operations include:

  • Move on the current screen
  • Move between screens
  • Going up and down stairs – only if it is possible to traverse them.
  • Collecting objects and update inventory

Refresh

This incorporates the following procedures:

Draw Frames

  • Draws playing frames

Draw Sprite

  • Processes the whole room to draw it in its totality

Inventory

  • Updates the title and list of objects collected

Saving / Loading

  • Allow the user the option of saving a game that he is halfway through.

Designing Units

These units incorporate everything needed to edit an existing game or to create a new one.

Sprites

These are the little graphics that will be used to animate the game. 
e.g. the main character, walls, doors, stairs, animals, stuff to collect

Sprite Unit

This unit is designed to edit sprites. That is the part of the sprite that you can see will be stored in a separate file.

Load Image

  • Opens the file specified by the parameter passed
  • Checks the header and file version
  • Allocates the required memory for the image
  • Reads the image header
  • Reads the image

Save Image

  • Opens the file specified by the parameter passed
  • Write header and file version
  • Write image with header

Edit Sprites

The header of this procedure contains lots of constant variables that are defined as rectangles. This is so that drawing and detecting whether the mouse is in one of the rectangles is very much easier.
  • Set-up data structures.
  • Check if pre-load is needed
  • Repeat
    • Check for key presses
    • Act on any keys appropriately
    • Check for mouse movement
    • Check for mouse in editing areas and buttons down and if so alter image to reflect user’s directions.
    • Check for mouse button click and act accordingly
    • Update display of mouse position over editing areas, or colour palette
  • Until user presses escape or clicks on exit
  • Update passed file name

Pre-Load

This procedure is called if the edit sprite procedure is passed a file name. It will load the image from the file and refresh the screen to indicate that the file has been automatically loaded.

Refresh

  • Draw Frames

This procedure draws all the frames around the drawing and editing areas. It also draws the buttons and the colour palette at the bottom of the screen.

  • Update Colours

This refreshes the indicator that shows the currently selected colours. It also prints the colour numbers.

  • Repeat Pattern

This takes the small image and repeats it many times so that a mosaic effect is created. This shows the user what the image would look like when titled together.

  • Enlarge Pattern

This reads the small image and enlarges it to the main editing window. This is only used in those procedures that only change the small image. I.e. normal editing handles both small and enlarged images.

Load / Save

Both of these procedures provide an interactive interface to the user so that he or she is able to load or save an image easily.
  • Load Image
    • Clear screen and set-up load frames
    • Save current image to memory
    • Get name for file to load
    • Load new image from file
    • Clear screen and redraw editing frames
    • Display new image or old image if load failed
    • Enlarge and tile new image
    • Update name of image on screen
  • Save Image
    • Clear screen and set-up save frames
    • Save current image to memory
    • Ask for file name to save as
    • Save image to file
    • Restore screen editing frames and image
    • Re-enlarge and tile image
    • Restore name of image on screen

Editing

  • Clear Pattern

    Clears the screen and all related image data, resets the name of the currently edited file.

  • Move Image

    This procedure is used to move the entire image one pixel’s worth in a certain direction.

  • Save current image, except for one pixel width on the leading edge
  • Clear current image
  • Load image back, but now in the new position.

Draw Sprites

  • This is a generic procedure to draw a table of sprites at any position on the screen with any number of columns and rows.

Convert BMP

  • This procedure asks the user for the name of a bitmap file and the name of a destination sprite file and proceeds to convert the bitmap image into a sprite. This is so that the user could use an alternative editor to edit images and then import them into Game Designer.

Mapping Unit

Each game will have a resource of 255 separate sprites – there images stored in separate files. Each separate sprite in the game will have different properties. This means that a sprite can be used for more than one thing in more than one game without storing the image twice.

Load Sprite Map

Opens the file referred to by the parameter passed

Read the file header and version

Loop for each sprite

  • If a call back procedure was specified, call it now.
  • Read the sprite’s file name
  • Load the sprite’s image using load image
  • Read the sprite’s name
  • Read the sprite’s properties
Return success or failure
Call-back procedure
This is another example of procedures being passed as pointers. The calling procedure can write a procedure and pass this procedure its address. Every time this procedure starts to load a new sprite it will call the procedure pointer to by the variable passed. This enabled the calling procedure to display a percentage bar of some sort. The call back procedure need not even exist let alone be the same for all loading and therefore much flexibility is extended.

Save Sprite Map

  • Opens the file referred to by the parameter passed
  • Save file header and version
  • Loop for each sprite
    • Write the sprite’s file name
    • Write the sprite’s name
    • Write the sprite’s properties
  • Return success or failure

Edit Sprite Map

  • Set-up data structures.
  • Repeat
    • Check for key presses
    • Act on any keys appropriately
    • Check for mouse movement
    • Check for mouse in property areas and buttons down and if so alter properties to reflect user’s directions. When appropriate call another procedure to facilitate the altering of the property
    • Check for mouse button click and act accordingly
    • Update display of mouse position over sprite table
  • Until user presses escape or clicks on exit

Properties

  • Is Solid

E.g. a wall

  • Is Collectable

The player can collect these things, and can put them down later

  • Can Play it

The user will be able to navigate around the game using one of these sprites.

  • To Vanish

The user uses this object to make this sprite disappear

  • Is Stairs

These allow the user to navigate up or down

  • To Traverse

The user must have this object to be able to go past, over, through, up, down this sprite

  • Is Deadly

If the player touches one of these they can die

  • To Protect

This object will protect the player from being killed. I.e. if players try to pass this point without the object – they will die.

Refresh

Clears the screen, draws the frames, draw the table of sprites, updates the currently selected sprite and draw the current sprite map’s filename.
Draw Frames

Draw the borders and buttons onto the screen. Draw the titles of the sprites’ properties.

Update Selected Sprite

Draw the currently selected