This is the main entry point for Invaders. At the top of this file, please note the .merge commands to load in the other source. Please refer to SWIFT help, however this is a very good feature, allowing moduled code development and when calling functions you will note the prefix (file name) before the function name. Allow flexable function names and is more readable.

   ;-------------------------------------------------------------------------------

   ;  Main  - Invaders ...

   ;  Written by Neil Beresford.

   ;

   ;

   ;  Copyright 2008,2009 Neil Beresford

   ;

   ;    This file is part of Sparse Invaders.

   ;    Sparse Invaders is free software: you can redistribute it and/or modify

   ;    it under the terms of the GNU General Public License as published by

   ;    the Free Software Foundation, either version 3 of the License, or

   ;    (at your option) any later version.

   ;

   ;    Sparse Invaders is distributed in the hope that it will be useful,

   ;    but WITHOUT ANY WARRANTY; without even the implied warranty of

   ;    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

   ;    GNU General Public License for more details.

   ;

   ;    You should have received a copy of the GNU General Public License

   ;    along with Sparse Invaders.  If not, see <http://www.gnu.org/licenses/>.

   ;

   ;

   ;

   ;-------------------------------------------------------------------------------

   

   .ORG $0900                         ; Good place to start, so it fits ...

   ;.ORG $0900

   

   .require "Constands"               ; BBC and general constants

   .require "Macros"                  ; general macros

   

   .merge   "ScreenFunctionality"     ; screen functionality

   .merge   "SpriteController"        ; Sprite controller and drawer

   ;.merge   "FileLoad"                ; File System loading 

   ;.merge   "Debug"                   ; debug functionality

   .merge   "Timer"                   ; VSync timer

   .merge   "Keyboard"                ; Keyboard handling

   .merge   "Invader_Player"          ; Invader code - player setup

   .merge   "BlockDrawer"             ; Block Drawer ...

   .merge   "Invader_Baddies"         ; Baddies for the invader game

   .merge   "Invader_Bullets"         ; Baddie bullets

   .merge   "Invader_Bases"           ; Bases, logic and drawing...

   .merge   "Invader_Hiscore"         ; Hiscore display...

   .merge   "Sound"                   ; Sound init and generation...

Main is the starting point (0x900), this initializes the sound, video, keyboard and timer etc.

   ;-------------------------------------------------------------------------------

   ;  Main - 

   ;     Main Entry Point

   ;-------------------------------------------------------------------------------

   

   Main:

  

      ; initialization of the system...

      jsr  Sound._INITSOUND

      `MODE 2

      `CURSOROFF

   

   

      jsr  ScreenFunctionality.Screen_Clear   ; clear the screen...

   

   

      jsr  SpriteController.SpriteInit          ; init the sprite system

   

      jsr  BlockDrawer.BlockInit                ; init the block system

      jsr  Keyboard.Keyboard_Init               ; setup the keyboard handling

   

   

      jsr  Timer.Timer_Init                     ; set the user timer off to handle VBlanks our own way...

      jsr  Invader_Hiscore.Invader_Hiscore_Init ; init the hiscore, only done here to allow the score to be kept between games

   

      LDA  #0

      STA  FIREBUTTON_DELAY

main_restart main drops through into 'main_restart'. At this point the game is setup, so this is a good point to jump to upon game over.

Intro screen is displayed, followed by start level screen - then clears and draws the score, life, invaders and bases.

   main_restart:

   

      LDA #0       ;fire bullet

      JSR Sound._MAKE_SOUND

     

      jsr  ScreenFunctionality.Screen_Clear  ; Display main message...

      jsr  Invader_Player.Player_GameMessage

      jsr  ScreenFunctionality.Screen_Clear  ; clear the screen...

   

      LDA #0       ;fire bullet

      JSR Sound._MAKE_SOUND

   

      ; main game initialization

      jsr  Invader_Baddies.BaddiesNewGame     ; initializes a new game

      jsr  Invader_Bases.Init

   

      jsr  Invader_Player.PlayerInit          ; initialize the player, 

      jsr  Invader_Baddies.BaddiesInit

          

      jsr  Invader_Player.Player_StartLevel

      jsr  ScreenFunctionality.Screen_Clear   ; clear the screen...

      LDA   #100

      STA   FIREBUTTON_DELAY

   

      ; pre-draw the screen ...

      jsr  ScreenFunctionality.DrawScore      ; draw score and lifes

      jsr  Invader_Baddies.BaddiesDraw        ; draw the invaders

      jsr  Invader_Bases.DrawBases            ; draw the bottom bases

   

      LDA #0       ;fire bullet

      JSR Sound._MAKE_SOUND

      

main_loop is the main game loop. It basically does the following

• Sprite Draw

• Game Logic

• Sprite Wipe

Please note the commented out macros that change the background colour. This allows for timing of functionality, I used to this when sorting out the game so it ran in one game timer frame. Once the game logic has been processed the loop waits for a vertical blank before removing the sprites.

   main_loop: 

   

      ;

      ;  Please note the importance of the spritewipe being just

      ;  before the spritedraw and where the vsync timer flag is 

      ;  placed...

      ;

   

   ;;   `BORDERCOLOUR 2

   

      jsr  SpriteController.SpritesDrawActive 

   

   ;;   `BORDERCOLOUR 3

   

      jsr  keyboard.Keyboard_checkkeys

      jsr  keyboard.Keyboard_MovePlayer

      jsr  Invader_Baddies.BaddiesUpdate

      jsr  Invader_Baddies.BaddiesUpdateMother

      jsr  Invader_Player.Player_BulletMove

      jsr  ScreenFunctionality.UpdateScreen

   

      jsr  Invader_Baddies.BaddiesGeneralUpdate

   

   ;;   `BORDERCOLOUR 0

   

      LDA  #0

      STA  TIMER_FLAG

   VB:

      LDA  TIMER_FLAG

      BEQ  VB

      LDA  #0

      STA  TIMER_FLAG

   

   ;;   `BORDERCOLOUR 1

    

      jsr  SpriteController.SpritesWipeActive 

      jsr  Invader_Bullets.Control

   

      jmp  main_loop

      

   end:   

      rts

      

   

   

   ;-------------------------------------------------------------------------------

   ;-------------------------------------------------------------------------------

   ; End of Main

   ;-------------------------------------------------------------------------------