Robotron: 2084: Routine at 52047

52047: Main Game Loop

Used by the routine at Stage_Next_Wave. Wave-active game loop entry, called from Stage_Next_Wave once the entity list and playfield are ready. Initialises the player's starting screen position and frame counters, copies the sprite template via Initialise_Wave_Start_Sprites, then falls into the per-frame control poll at Main_Loop_Poll. Each frame: reads the controller via Read_Control_Input, moves and redraws the player sprite, spawns one new entity every three frames adjacent to the player, dispatches all active entity handlers via DispatchWordFromHL, updates the colour bar and protection checks, then loops back to Main_Loop_Poll.
Initialise the player's screen position and frame counters for the start of the wave.
Main_Game_Loop	52047	LD HL,50388	Point HL at Player_Y_Position and set the starting screen row to 92.
	52050	LD (HL),92
	52052	INC HL
	52053	LD (HL),125	Set the starting screen column to 125 and reset the wave-start delay counter at Wave_Start_Delay to 26.
	52055	LD A,26
	52057	LD (50483),A
	52060	LD A,15	Set the animation frame counters at Animation_Frame_Counter_One and Animation_Frame_Counter_Two to 15 and copy the sprite template via Initialise_Wave_Start_Sprites.
	52062	LD (50484),A
	52065	LD (50486),A
	52068	CALL Initialise_Wave_Start_Sprites
This entry point is used by the routine at Dispatch_Narrow_Entity_Approach. Per-frame start: check whether the wave is still active before processing input.
Main_Loop_Poll	52071	LD A,(50483)	If the wave-start delay counter at Wave_Start_Delay is non-zero, jump to Dispatch_Narrow_Entity_Approach (wave-end / game-over handling).
	52074	AND A
	52075	JP NZ,Dispatch_Narrow_Entity_Approach
This entry point is used by the routine at Animate_Wave_Start_Sequence. Read the controller and map the input to player movement directions.
Main_Loop_Frame	52078	CALL Read_Control_Input	Read the controller state via Read_Control_Input.
	52081	LD A,C	Apply vertical input processing via Compute_Entity_Approach_Position_Short and store the result in C.
	52082	CALL Compute_Entity_Approach_Position_Short
	52085	LD C,A
	52086	LD A,B	Apply horizontal input processing via Compute_Entity_Approach_Position and store the result in B.
	52087	CALL Compute_Entity_Approach_Position
	52090	LD B,A
	52091	CP 15	If the direction is neutral (15), skip to Main_Loop_Update_Y.
	52093	JR Z,Main_Loop_Update_Y
	52095	LD (50456),A	Store the updated X direction at Player_X_Direction.
Main_Loop_Update_Y	52098	LD A,C	If the vertical direction changed, store it at Player_Y_Direction.
	52099	CP 15
	52101	JR Z,Main_Loop_Move_Player
	52103	LD (50455),A
Move the player sprite if a direction was input. Neutral direction (15) means no movement — skip directly to entity spawning.
Main_Loop_Move_Player	52106	LD A,B	If no horizontal direction, skip to Main_Loop_Entity_Spawn.
	52107	CP 15
	52109	JR Z,Main_Loop_Entity_Spawn
	52111	LD E,A	Build the sprite frame word offset from the X direction and stash it; point HL at Intro_Closing_Sprite and erase the current player sprite via Erase_Entity_Sprite.
	52112	SLA E
	52114	LD D,0
	52116	PUSH DE
	52117	LD HL,50387
	52120	CALL Erase_Entity_Sprite	Erase the current player sprite via Erase_Entity_Sprite.
	52123	POP DE	Look up the movement delta for the current direction in the table at Movement_Delta_Table; add the Y delta to Player_Y_Position.
	52124	LD HL,50862
	52127	ADD HL,DE
	52128	EX DE,HL
	52129	LD HL,50388
	52132	LD A,(DE)
	52133	ADD A,(HL)
	52134	CP 16
	52136	JR C,Main_Loop_Clamp_X
	52138	CP 173	Reject the Y move if the new position is above the playfield top or below the bottom edge.
	52140	JR NC,Main_Loop_Clamp_X
	52142	LD (HL),A	Write the updated Y position.
Main_Loop_Clamp_X	52143	INC HL	Add the X delta to Player_X_Position.
	52144	INC DE
	52145	LD A,(DE)
	52146	ADD A,(HL)
	52147	CP 8
	52149	JR C,Main_Loop_Update_Sprite	Reject the X move if the new position is past the left edge.
	52151	CP 242
	52153	JR NC,Main_Loop_Update_Sprite	Reject the X move if past the right edge.
	52155	LD (HL),A	Write the updated X position.
Select the sprite frame for the new direction and redraw the player.
Main_Loop_Update_Sprite	52156	LD A,(50456)	Look up the sprite frame index for the current X direction in Sprite_Frame_Table; write it to Intro_Closing_Sprite.
	52159	LD E,A
	52160	LD D,0
	52162	LD HL,54816
	52165	ADD HL,DE
	52166	EX DE,HL
	52167	LD A,(DE)
	52168	LD HL,50387
	52171	LD (HL),A
	52172	EXX	Set the player colour to INK: WHITE, PAPER: BLACK (BRIGHT) in B' and redraw the player sprite via Draw_Entity_Sprite.
	52173	LD B,71
	52175	EXX
	52176	CALL Draw_Entity_Sprite
Every three frames spawn one new entity adjacent to the player.
Main_Loop_Entity_Spawn	52179	LD HL,50383	Decrement the entity spawn timer at Entity_Spawn_Timer.
	52182	DEC (HL)	Decrement the entity spawn timer at Entity_Spawn_Timer.
	52183	JP NZ,Main_Loop_Entity_Update	If the timer has not reached zero, skip to Main_Loop_Entity_Update.
	52186	LD (HL),3	Reset the spawn timer to 3.
	52188	LD HL,(50385)	Load the entity list end pointer from Playfield_Entity_List_Pointer and write the movement handler address Move_And_Redraw_Entity to the entity list.
	52191	LD DE,54749
	52194	LD (HL),E	Advance past the handler address word in the entity list.
	52195	INC HL
	52196	LD (HL),D
	52197	INC HL
	52198	LD (50394),HL	Save the entity record write pointer to Entity_Record_Pointer.
	52201	LD A,(50455)	Load the Y direction index from Player_Y_Direction.
	52204	EX DE,HL	Index the entity type table at Entity_Type_By_Direction_Table by Y direction and write the entity type to the entity record.
	52205	LD C,A
	52206	LD B,0
	52208	LD HL,54513
	52211	ADD HL,BC
	52212	EX DE,HL
	52213	LD A,(DE)
	52214	LD (HL),A
	52215	INC HL	Advance to the next entity record field.
	52216	LD A,(50455)	Load the Y direction again, scale it to a byte offset (×8), and look up the sprite pixel offsets in Narrow_Entity_Sprite_Data.
	52219	LD C,A
	52220	SLA C
	52222	SLA C
	52224	SLA C
	52226	LD B,0	Clear the high byte of the offset and index into Narrow_Entity_Sprite_Data.
	52228	EX DE,HL
	52229	LD HL,51151
	52232	ADD HL,BC	Add the direction offset to the sprite data base address.
	52233	LD A,(50388)	Compute the entity's initial Y position from Player_Y_Position plus the sprite Y offset; write both bytes to the entity record.
	52236	ADD A,(HL)
	52237	LD (DE),A
	52238	INC HL
	52239	INC DE
	52240	LD A,(50389)
	52243	ADD A,(HL)	Write the X position bytes derived from Player_X_Position.
	52244	LD (DE),A
	52245	INC HL
	52246	INC DE
	52247	LD A,(50388)	Add the sprite Y check offset to the player Y position and reject the spawn if the result is above the playfield top edge.
	52250	ADD A,(HL)
	52251	CP 16
	52253	JR C,Main_Loop_Abort_Spawn	Reject the spawn if the Y position is below the playfield bottom edge (184).
	52255	CP 184
	52257	JR NC,Main_Loop_Abort_Spawn	Reject if below the bottom edge.
	52259	LD (DE),A	Write the validated Y position field to the entity record.
	52260	INC HL
	52261	INC DE
	52262	LD A,(50389)	Check the X position is within the playfield horizontal bounds (8–247).
	52265	ADD A,(HL)
	52266	CP 8
	52268	JR C,Main_Loop_Abort_Spawn	Reject the spawn if the X position is past the left edge.
	52270	CP 248	Reject the spawn if the X position is past the left edge.
	52272	JR NC,Main_Loop_Abort_Spawn	Reject if past the right edge.
	52274	LD (DE),A	Write the validated X position field to the entity record.
	52275	INC HL
	52276	INC DE
	52277	LD BC,4	Copy the remaining four entity record bytes via LDIR.
	52280	LDIR	Copy the remaining four entity record bytes via LDIR.
	52282	EX DE,HL	Mark the end of the entity record and update the entity list end pointer at Playfield_Entity_List_Pointer.
	52283	LD (HL),255
	52285	INC HL
	52286	LD (50385),HL
	52289	LD E,1	Initialise the entity via Initialise_Entity_State.
	52291	CALL Initialise_Entity_State	Initialise the entity via Initialise_Entity_State.
	52294	LD HL,(50394)	Reload the entity record pointer from Entity_Record_Pointer and set the entity colour to INK: WHITE, PAPER: BLACK (BRIGHT) in B'.
	52297	EXX
	52298	LD B,71
	52300	EXX
	52301	CALL Draw_Narrow_Entity_Sprite	Draw the spawned entity sprite via Draw_Narrow_Entity_Sprite.
	52304	LD HL,(50385)	Reload the entity list end pointer from Playfield_Entity_List_Pointer.
Main_Loop_Write_Terminator	52307	LD DE,52834	Write the playfield entity handler 52834 and the 255 sentinel as the entity list terminator.
	52310	LD (HL),E
	52311	INC HL
	52312	LD (HL),D
	52313	INC HL
	52314	LD (HL),255
Dispatch all active entity handlers, update animation and colour bar.
Main_Loop_Entity_Update	52316	LD HL,24832	Set HL to the start of the entity list at Entity_List_Base.
	52319	CALL DispatchWordFromHL	Dispatch all entity handlers in the list via DispatchWordFromHL.
	52322	LD HL,(50459)	Decrement the animation counter at Animation_Frame_Pair if it is non-zero.
	52325	LD A,H
	52326	OR L
	52327	JR Z,Main_Loop_Colour_Bar_Update
	52329	DEC HL
	52330	LD (50459),HL
Main_Loop_Colour_Bar_Update	52333	CALL UpdateAttributeBar	Update the colour bar via UpdateAttributeBar, run the protection check via CheckScoreAwardLife, and call the game state update via Dispatch_Entity_State_Handler.
	52336	CALL CheckScoreAwardLife
	52339	CALL Dispatch_Entity_State_Handler
	52342	CALL CheckScoreAwardLife_SessionGate	Run the copy protection gate via CheckScoreAwardLife_SessionGate and loop back to Main_Loop_Poll.
	52345	JP Main_Loop_Poll
Out-of-bounds abort: the new entity would fall outside the playfield. Skip the spawn but still write the entity list terminator.
Main_Loop_Abort_Spawn	52348	LD HL,(50385)	Reload the entity list end pointer from Playfield_Entity_List_Pointer and jump to Main_Loop_Write_Terminator.
	52351	JR Main_Loop_Write_Terminator