Routines
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57347: Process Entity Record
Processes one entity slot in the wave entity list. If the slot is active, the enemy's animation colours are updated on screen via Paint_Narrow_Entity_Attributes and its animation counter decremented. If the counter expires the enemy is erased and the slot retired. If the slot holds spawn data (Process_Entity_Record_Inactive), a new enemy position is found and the enemy is placed in the play area.
Input
HL Pointer to the entity type/state byte
Process_Entity_Record_Fast 57347 LD A,(HL) Read the entity's animation counter.
57348 JP Process_Entity_Record_Tick Jump to Process_Entity_Record_Tick.
Process_Entity_Record 57351 LD A,(HL) Read the entity's animation counter.
57352 AND A Jump to Process_Entity_Record_Inactive if the entity slot is inactive.
57353 JP Z,Process_Entity_Record_Inactive
Update the enemy's on-screen colour then advance its animation counter. If the counter expires the enemy is erased.
Process_Entity_Record_Tick 57356 AND %00000111 Extract the three-bit animation frame number.
57358 INC HL Move past the animation counter byte.
57359 PUSH HL Stash the entity data pointer on the stack.
57360 EXX Pass the animation frame number to the colouring routine.
57361 LD B,A
57362 EXX
57363 CALL Paint_Narrow_Entity_Attributes Call Paint_Narrow_Entity_Attributes to colour the entity on screen.
57366 POP HL Restore the entity data pointer from the stack.
57367 DEC HL Step back to the animation counter byte.
57368 DEC (HL) Advance the animation frame and jump to Process_Entity_Record_Next7 if not yet expired.
57369 JP NZ,Process_Entity_Record_Next7
The animation counter has run down to zero: remove the enemy from the screen.
57372 INC HL Move past the animation counter byte.
57373 PUSH HL Stash the entity data pointer on the stack.
57374 CALL Erase_Entity_Sprite Call Erase_Entity_Sprite to erase the enemy sprite from the screen.
57377 POP HL Restore the entity data pointer from the stack.
57378 DEC HL Step back to the entity handler address field.
57379 DEC HL
57380 DEC HL
57381 LD DE,57388 Load Process_Entity_Record_Next7 as the replacement entity handler.
57384 LD (HL),E Write Process_Entity_Record_Next7 into the entity handler address field.
57385 INC HL
57386 LD (HL),D
57387 INC HL
This entry point is used by the routines at Handle_Homing_Enemy and Animate_Wall_Bouncing_Enemy_Death.
Process_Entity_Record_Next7 57388 LD DE,7 Skip to the next entity record and return.
57391 ADD HL,DE
57392 RET
This slot holds spawn data for a new enemy. Erase any ghost at the target position, check it falls within the play area, then try to place the enemy.
Process_Entity_Record_Inactive 57393 INC HL Move past the animation counter byte.
57394 PUSH HL Stash the entity data pointer on the stack.
57395 CALL Erase_Wide_Entity_Sprite Call Erase_Wide_Entity_Sprite to erase any residual sprite at the spawn position.
57398 POP HL Restore the entity data pointer from the stack.
57399 INC HL Move to the entity's Y position.
57400 EXX Set the play area boundary data address for the bounds check.
57401 LD HL,50388
57404 EXX
57405 CALL HitTestBounds8AtHL Call HitTestBounds8AtHL to test if the spawn position is within the play area.
57408 JP NC,Process_Entity_Record_Kill Jump to Process_Entity_Record_Kill if the position is outside the play area.
57411 DEC HL Step back to the entity type state byte.
57412 DEC HL
57413 DEC HL
57414 CALL Generate_Random_Byte Call Generate_Random_Byte to determine whether the enemy should change type.
57417 CP 240 Stay with the current enemy type if the random roll is below 240.
57419 JP C,Process_Entity_Record_Keep_Type
Process_Entity_Record_Cycle_Type 57422 DEC HL Step back to the entity type state byte.
57423 LD A,(HL) Read the entity type state.
57424 INC A Advance to the next animation variant.
57425 AND %00110011 Wrap within the valid entity type range (51).
57427 LD (HL),A Save the new entity type state.
57428 INC HL Move to the entity's animation frame data.
57429 JP Process_Entity_Record_Apply_Delta Jump to Process_Entity_Record_Apply_Delta.
The random roll was below 240 so the enemy keeps its current type. Load the unchanged type state and fall through to apply a movement step.
Process_Entity_Record_Keep_Type 57432 DEC HL Step back to the entity type state byte.
57433 LD A,(HL) Read the entity type state.
57434 INC HL Move to the entity's animation frame data.
Apply a one-step movement from the direction table at Direction_Delta_Table. The direction is derived from the low two bits of the entity type state.
Process_Entity_Record_Apply_Delta 57435 EX DE,HL Preserve the entity data pointer in DE.
57436 AND %00000011 Isolate the movement direction (two bits).
57438 SLA A Index into the direction delta table at Direction_Delta_Table.
57440 LD C,A
57441 LD B,0
57443 LD HL,57626
57446 ADD HL,BC
57447 EX DE,HL Restore HL to the entity data and DE to the delta entry.
57448 LD A,(DE) Apply the Y movement delta to the enemy's current Y position.
57449 ADD A,(HL)
57450 CP 171 Retry with a new type if the enemy moves below the play area.
57452 JP NC,Process_Entity_Record_Cycle_Type
57455 CP 16 Retry with a new type if the enemy moves above the play area.
57457 JP C,Process_Entity_Record_Cycle_Type
57460 LD C,A Save the validated Y position.
57461 INC HL Advance to the enemy's X position and the X delta.
57462 INC DE
57463 LD A,(DE) Apply the X movement delta to the enemy's current X position.
57464 ADD A,(HL)
57465 CP 241 Jump to Process_Entity_Record_Retry if the new X overshoots the right edge.
57467 JP NC,Process_Entity_Record_Retry
57470 CP 8 Accept the position if it is within the play area's left boundary.
57472 JP NC,Process_Entity_Record_Register
Process_Entity_Record_Retry 57475 DEC HL Step back to the Y delta entry.
57476 JP Process_Entity_Record_Cycle_Type Retry with a new enemy type.
The enemy's new position is inside the play area. Write it to the record and draw the enemy on screen.
Process_Entity_Record_Register 57479 LD (HL),A Write the new screen position into the entity record.
57480 DEC HL
57481 LD (HL),C
57482 DEC HL
57483 PUSH HL Stash the entity record pointer on the stack.
57484 EXX Set the spawn display attribute (INK: WHITE, PAPER: BLACK (BRIGHT) ) in the shadow register.
57485 LD B,71
57487 EXX
57488 CALL Draw_Wide_Entity_Sprite Call Draw_Wide_Entity_Sprite to spawn the enemy and draw it on screen.
57491 POP HL Restore the entity record pointer from the stack.
This entry point is used by the routines at Handle_Homing_Enemy, Handle_Horizontal_Enemy_Entity, Animate_Wall_Bouncing_Enemy_Death, Process_Replacement_Enemy_Entity and Process_Final_Phase_Enemy_Entity.
Process_Entity_Record_Next6 57492 LD DE,6 Skip to the next entity record and return.
57495 ADD HL,DE
57496 RET
This entry point is used by the routine at Handle_Horizontal_Enemy_Entity.
The enemy was placed successfully. Increment the scroll position counter before advancing to the next record.
Process_Entity_Record_Counter_Up_Next6 57497 EX DE,HL Preserve the entity list pointer in DE.
57498 LD HL,(50485) Add 64 to *50485.
57501 LD BC,64
57504 ADD HL,BC
57505 LD (50485),HL
57508 EX DE,HL Restore the entity list pointer.
57509 JP Process_Entity_Record_Next6 Jump to Process_Entity_Record_Next6.
This entry point is used by the routine at Handle_Homing_Enemy.
Same as Process_Entity_Record_Counter_Up_Next6 but steps over a seven-byte record.
Process_Entity_Record_Counter_Up_Next7 57512 EX DE,HL Preserve the entity list pointer in DE.
57513 LD HL,(50485) Add 64 to *50485.
57516 LD BC,64
57519 ADD HL,BC
57520 LD (50485),HL
57523 EX DE,HL Restore the entity list pointer.
57524 JP Process_Entity_Record_Next7 Jump to Process_Entity_Record_Next7.
The enemy has left the play area. Flash it with its death sprite then add a kill bonus to the player's score.
Process_Entity_Record_Kill 57527 DEC HL Rewind to the entity handler address field.
57528 DEC HL
57529 DEC HL
57530 DEC HL
57531 DEC HL
57532 LD (HL),50 Switch the entity to the kill sequence handler.
57534 INC HL Move to the entity colour attribute byte.
57535 LD A,(HL) Read the entity colour attribute.
57536 PUSH AF Stash the entity colour attribute on the stack.
57537 LD A,(50398) Set the entity's death colour from the current kill tally.
57540 ADD A,19
57542 LD (HL),A
57543 PUSH HL Stash the attribute pointer on the stack.
57544 EXX Set the death flash attribute ( WHITE) in the shadow register.
57545 LD B,7
57547 EXX
57548 CALL Draw_Entity_Sprite Call Draw_Entity_Sprite to draw the entity's death animation sprite.
57551 POP HL Restore the attribute pointer from the stack.
57552 LD A,(50398) Read the enemy kill value from the wave counter.
57555 SLA A Multiply by 16 for the score contribution.
57557 SLA A
57559 SLA A
57561 SLA A
57563 EX DE,HL Save the entity pointer while accessing the score.
57564 LD HL,50181 Point HL at the player's score.
57567 ADD A,(HL) Add the kill score to the ones digit of the player's score (BCD).
57568 DAA
57569 LD (HL),A
57570 JP NC,Process_Entity_Record_Wave_Count Jump to Process_Entity_Record_Wave_Count if the ones digit did not overflow.
57573 DEC HL Move to the tens digit.
57574 LD A,1 Carry one into the tens digit of the player's score (BCD).
57576 ADD A,(HL)
57577 DAA
57578 LD (HL),A
57579 JP NC,Process_Entity_Record_Wave_Count Jump to Process_Entity_Record_Wave_Count if the tens digit did not overflow.
57582 DEC HL Move to the hundreds digit.
57583 LD A,1 Carry one into the hundreds digit of the player's score (BCD).
57585 ADD A,(HL)
57586 DAA
57587 LD (HL),A
Process_Entity_Record_Wave_Count 57588 LD A,(50398) Jump to Process_Entity_Record_Decrement_Count if the maximum kill count for this wave is reached.
57591 CP 5
57593 JP Z,Process_Entity_Record_Decrement_Count
57596 INC A Increment the wave kill counter.
57597 LD (50398),A
Process_Entity_Record_Decrement_Count 57600 POP AF Restore the entity colour attribute from the stack.
57601 SRL A Extract the entity type to use as a count table index.
57603 SRL A
57605 SRL A
57607 SRL A
57609 LD C,A
57610 LD B,0 Form a pointer to the entity count entry for this type.
57612 LD HL,50215
57615 ADD HL,BC
57616 DEC (HL) Decrement the on-screen enemy count for this type.
57617 EX DE,HL Restore the entity list pointer.
57618 PUSH HL Stash the entity list pointer on the stack.
57619 CALL Clear_Colour_Bar_Column Call Clear_Colour_Bar_Column to update the score and wave display.
57622 POP HL Restore the entity list pointer from the stack.
57623 JP Process_Entity_Record_Next6 Jump to Process_Entity_Record_Next6.
Movement delta table: one two-byte entry (Y delta, X delta) per cardinal direction, indexed by the low two bits of the entity type state. Order: up, right, down, left.
Direction_Delta_Table 57626 DEFB 255,0
57628 DEFB 0,1
57630 DEFB 1,0
57632 DEFB 0,255
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