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Routines |
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Used by the routine at GameStart.
The real start of the game. It checks the loader's signature, clears the game variables, builds the lookup tables, shows the title screen and menu, sets up the first player and then falls into the main loop at MainLoop.
When a game has ended and the high score has been shown, control comes back to RestartGame so that the title screen is shown again.
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| InitialiseGame | 41837 | LD SP,24064 | Reset the stack pointer to just below the start of the game. | |
| 41840 | LD A,(23673) | Fetch the high byte of the system frame counter. | ||
| 41843 | CP 86 | Return unless it holds 86 which is the value the tape loader leaves there. | ||
| 41845 | RET NZ | |||
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Clear the game variables.
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| 41846 | LD HL,41479 | Clear everything from MovementSoundCounter onwards, 358 bytes in all, which covers every game variable. | ||
| 41849 | LD BC,358 | |||
| 41852 | JR InitialiseGame_Clear | Skip over the shorter clear below. | ||
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This entry point is used by the routine at CheckTopScore.
This entry point is used when the game has ended. It keeps the frame counter, the random seeds and the control method chosen on the menu.
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| RestartGame | 41854 | LD HL,41532 | Clear everything from SoundNotesLeft onwards, 305 bytes in all. | |
| 41857 | LD BC,305 | |||
| InitialiseGame_Clear | 41860 | CALL FillMemory | Fill the memory with zero. | |
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Set up the machine and show the title screen.
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| 41863 | CALL BuildShiftTables | Build the pixel shifting lookup tables. | ||
| 41866 | LD A,195 | Write the opcode for a 195 (JP) instruction to SpriteJumpOpcode, ready for the sprite drawing routines to use. | ||
| 41868 | LD (41508),A | |||
| 41871 | XOR A | Set the border to black. | ||
| 41872 | OUT (254),A | |||
| 41874 | CALL GameMenu | Show the title screen and wait for the player to start the game. | ||
| 41877 | LD A,(41500) | Fetch the option flags. | ||
| 41880 | OR %00001000 | Set bit 3, which records that a game is under way. | ||
| 41882 | LD (41500),A | Store the option flags again. | ||
| 41885 | CALL PrepareTopScoreText | Convert the top score into text for the telegram panel. | ||
| 41888 | CALL SetUpPlayers | Give both players their starting values. | ||
| 41891 | CALL ClearBuffer | Clear the off-screen playfield buffer. | ||
| 41894 | LD A,1 | Write 1 to StageRunningFlag to show that a new stage is starting. | ||
| 41896 | LD (41536),A | |||
| 41899 | LD A,(41500) | Fetch the option flags again. | ||
| 41902 | BIT 0,A | Test bit 0, which is set for a two player game. | ||
| 41904 | CALL NZ,ShowPlayerNumber | Print the current player number if there are two players. | ||
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Draw the screen for the next stage of the game and run it.
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| StartStage | 41907 | LD A,(41574) | Fetch the border and paper colour for the stage and keep the stage colour in E. | |
| 41910 | LD E,A | |||
| 41911 | CALL DrawGameScreen | Draw the screen furniture. | ||
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The main loop. It runs once for every frame of the game.
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| MainLoop | 41914 | XOR A | Write 0 to ObjectsDrawnCount to clear the count of objects drawn this frame. | |
| 41915 | LD (41539),A | |||
| 41918 | LD SP,24064 | Reset the stack pointer, so that nothing can build up on the stack. | ||
| 41921 | CALL CheckSheriffLost | Check whether the player has been lost and deal with it if so. | ||
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Run the handler for each of the fifteen object slots in turn.
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| 41924 | LD IX,41597 | Point IX at ObjectSlot_01. | ||
| MainLoopNextObject | 41928 | LD A,(IX+0) | Fetch the type of the object in this slot. | |
| 41931 | LD BC,42002 | Point BC at ObjectHandlerTable. | ||
| 41934 | CALL RunTableRoutine | Call the handler for the type of object. | ||
| 41937 | CALL UpdateRandomNumbers | Update the random number seeds. | ||
| 41940 | LD BC,16 | Set the size of an object slot in BC. | ||
| 41943 | ADD IX,BC | Move IX on to the next slot. | ||
| 41945 | PUSH IX | Copy the slot address into HL (using the stack). | ||
| 41947 | POP HL | |||
| 41948 | LD BC,41837 | The address past the last object slot goes into BC. | ||
| 41951 | AND A | Loop back to MainLoopNextObject until IX has moved past the last slot. | ||
| 41952 | SBC HL,BC | |||
| 41954 | JR C,MainLoopNextObject | |||
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Now do everything which does not belong to a single object.
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| 41956 | CALL AdvanceFrameCounter | Advance the frame counter. | ||
| 41959 | CALL RunStageScript | Create any objects which the current stage needs. | ||
| 41962 | CALL DrawScenery | Draw the scenery sprites. | ||
| 41965 | CALL DrawTown | Draw the town. | ||
| 41968 | CALL FlashChamber | Flash the chamber of the revolver which has just fired. | ||
| 41971 | CALL CopyBufferAndClear | Copy the playfield buffer to the screen. | ||
| 41974 | CALL PlaySoundEffect | Play the next note of any sound effect. | ||
| 41977 | CALL TypeTelegram | Print the next letter of the telegram. | ||
| 41980 | CALL FinishTownStage | Check whether the outlaw has been caught. | ||
| 41983 | CALL CreateTownObjects | Create new townspeople, the outlaw and the other town objects. | ||
| 41986 | CALL PauseGame | Pause the game if the pause key is being pressed. | ||
| 41989 | LD A,(41572) | Fetch the number of targets remaining in the stage and keep the number of targets left in C. | ||
| 41992 | LD C,A | |||
| 41993 | LD A,(41539) | Fetch the count of objects drawn this frame. | ||
| 41996 | OR C | Combine the two counts. | ||
| 41997 | JP Z,ReturnToTown | Jump to ReturnToTown if the stage has nothing left to do. | ||
| 42000 | JR MainLoop | Otherwise loop back to MainLoop for the next frame. | ||
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