Routines
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E003: 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 E003 LD A,(HL) Read the entity's animation counter.
E004 JP Process_Entity_Record_Tick Jump to Process_Entity_Record_Tick.
Process_Entity_Record E007 LD A,(HL) Read the entity's animation counter.
E008 AND A Jump to Process_Entity_Record_Inactive if the entity slot is inactive.
E009 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 E00C AND %00000111 Extract the three-bit animation frame number.
E00E INC HL Move past the animation counter byte.
E00F PUSH HL Stash the entity data pointer on the stack.
E010 EXX Pass the animation frame number to the colouring routine.
E011 LD B,A
E012 EXX
E013 CALL Paint_Narrow_Entity_Attributes Call Paint_Narrow_Entity_Attributes to colour the entity on screen.
E016 POP HL Restore the entity data pointer from the stack.
E017 DEC HL Step back to the animation counter byte.
E018 DEC (HL) Advance the animation frame and jump to Process_Entity_Record_Next7 if not yet expired.
E019 JP NZ,Process_Entity_Record_Next7
The animation counter has run down to zero: remove the enemy from the screen.
E01C INC HL Move past the animation counter byte.
E01D PUSH HL Stash the entity data pointer on the stack.
E01E CALL Erase_Entity_Sprite Call Erase_Entity_Sprite to erase the enemy sprite from the screen.
E021 POP HL Restore the entity data pointer from the stack.
E022 DEC HL Step back to the entity handler address field.
E023 DEC HL
E024 DEC HL
E025 LD DE,$E02C Load Process_Entity_Record_Next7 as the replacement entity handler.
E028 LD (HL),E Write Process_Entity_Record_Next7 into the entity handler address field.
E029 INC HL
E02A LD (HL),D
E02B INC HL
This entry point is used by the routines at Handle_Homing_Enemy and Animate_Wall_Bouncing_Enemy_Death.
Process_Entity_Record_Next7 E02C LD DE,$0007 Skip to the next entity record and return.
E02F ADD HL,DE
E030 RET
This slot holds spawn data for a new enemy. Erase any ghost at the target position, check it falls within the play area, then try to place the enemy.
Process_Entity_Record_Inactive E031 INC HL Move past the animation counter byte.
E032 PUSH HL Stash the entity data pointer on the stack.
E033 CALL Erase_Wide_Entity_Sprite Call Erase_Wide_Entity_Sprite to erase any residual sprite at the spawn position.
E036 POP HL Restore the entity data pointer from the stack.
E037 INC HL Move to the entity's Y position.
E038 EXX Set the play area boundary data address for the bounds check.
E039 LD HL,$C4D4
E03C EXX
E03D CALL HitTestBounds8AtHL Call HitTestBounds8AtHL to test if the spawn position is within the play area.
E040 JP NC,Process_Entity_Record_Kill Jump to Process_Entity_Record_Kill if the position is outside the play area.
E043 DEC HL Step back to the entity type state byte.
E044 DEC HL
E045 DEC HL
E046 CALL Generate_Random_Byte Call Generate_Random_Byte to determine whether the enemy should change type.
E049 CP $F0 Stay with the current enemy type if the random roll is below F0.
E04B JP C,Process_Entity_Record_Keep_Type
Process_Entity_Record_Cycle_Type E04E DEC HL Step back to the entity type state byte.
E04F LD A,(HL) Read the entity type state.
E050 INC A Advance to the next animation variant.
E051 AND %00110011 Wrap within the valid entity type range (33).
E053 LD (HL),A Save the new entity type state.
E054 INC HL Move to the entity's animation frame data.
E055 JP Process_Entity_Record_Apply_Delta Jump to Process_Entity_Record_Apply_Delta.
The random roll was below F0 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 E058 DEC HL Step back to the entity type state byte.
E059 LD A,(HL) Read the entity type state.
E05A 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 E05B EX DE,HL Preserve the entity data pointer in DE.
E05C AND %00000011 Isolate the movement direction (two bits).
E05E SLA A Index into the direction delta table at Direction_Delta_Table.
E060 LD C,A
E061 LD B,$00
E063 LD HL,$E11A
E066 ADD HL,BC
E067 EX DE,HL Restore HL to the entity data and DE to the delta entry.
E068 LD A,(DE) Apply the Y movement delta to the enemy's current Y position.
E069 ADD A,(HL)
E06A CP $AB Retry with a new type if the enemy moves below the play area.
E06C JP NC,Process_Entity_Record_Cycle_Type
E06F CP $10 Retry with a new type if the enemy moves above the play area.
E071 JP C,Process_Entity_Record_Cycle_Type
E074 LD C,A Save the validated Y position.
E075 INC HL Advance to the enemy's X position and the X delta.
E076 INC DE
E077 LD A,(DE) Apply the X movement delta to the enemy's current X position.
E078 ADD A,(HL)
E079 CP $F1 Jump to Process_Entity_Record_Retry if the new X overshoots the right edge.
E07B JP NC,Process_Entity_Record_Retry
E07E CP $08 Accept the position if it is within the play area's left boundary.
E080 JP NC,Process_Entity_Record_Register
Process_Entity_Record_Retry E083 DEC HL Step back to the Y delta entry.
E084 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 E087 LD (HL),A Write the new screen position into the entity record.
E088 DEC HL
E089 LD (HL),C
E08A DEC HL
E08B PUSH HL Stash the entity record pointer on the stack.
E08C EXX Set the spawn display attribute (INK: WHITE, PAPER: BLACK (BRIGHT) ) in the shadow register.
E08D LD B,$47
E08F EXX
E090 CALL Draw_Wide_Entity_Sprite Call Draw_Wide_Entity_Sprite to spawn the enemy and draw it on screen.
E093 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 E094 LD DE,$0006 Skip to the next entity record and return.
E097 ADD HL,DE
E098 RET
This entry point is used by the routine at Handle_Horizontal_Enemy_Entity.
The enemy was placed successfully. Increment the scroll position counter before advancing to the next record.
Process_Entity_Record_Counter_Up_Next6 E099 EX DE,HL Preserve the entity list pointer in DE.
E09A LD HL,($C535) Add 40 to *C535.
E09D LD BC,$0040
E0A0 ADD HL,BC
E0A1 LD ($C535),HL
E0A4 EX DE,HL Restore the entity list pointer.
E0A5 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 E0A8 EX DE,HL Preserve the entity list pointer in DE.
E0A9 LD HL,($C535) Add 40 to *C535.
E0AC LD BC,$0040
E0AF ADD HL,BC
E0B0 LD ($C535),HL
E0B3 EX DE,HL Restore the entity list pointer.
E0B4 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 E0B7 DEC HL Rewind to the entity handler address field.
E0B8 DEC HL
E0B9 DEC HL
E0BA DEC HL
E0BB DEC HL
E0BC LD (HL),$32 Switch the entity to the kill sequence handler.
E0BE INC HL Move to the entity colour attribute byte.
E0BF LD A,(HL) Read the entity colour attribute.
E0C0 PUSH AF Stash the entity colour attribute on the stack.
E0C1 LD A,($C4DE) Set the entity's death colour from the current kill tally.
E0C4 ADD A,$13
E0C6 LD (HL),A
E0C7 PUSH HL Stash the attribute pointer on the stack.
E0C8 EXX Set the death flash attribute ( WHITE) in the shadow register.
E0C9 LD B,$07
E0CB EXX
E0CC CALL Draw_Entity_Sprite Call Draw_Entity_Sprite to draw the entity's death animation sprite.
E0CF POP HL Restore the attribute pointer from the stack.
E0D0 LD A,($C4DE) Read the enemy kill value from the wave counter.
E0D3 SLA A Multiply by 10 for the score contribution.
E0D5 SLA A
E0D7 SLA A
E0D9 SLA A
E0DB EX DE,HL Save the entity pointer while accessing the score.
E0DC LD HL,$C405 Point HL at the player's score.
E0DF ADD A,(HL) Add the kill score to the ones digit of the player's score (BCD).
E0E0 DAA
E0E1 LD (HL),A
E0E2 JP NC,Process_Entity_Record_Wave_Count Jump to Process_Entity_Record_Wave_Count if the ones digit did not overflow.
E0E5 DEC HL Move to the tens digit.
E0E6 LD A,$01 Carry one into the tens digit of the player's score (BCD).
E0E8 ADD A,(HL)
E0E9 DAA
E0EA LD (HL),A
E0EB JP NC,Process_Entity_Record_Wave_Count Jump to Process_Entity_Record_Wave_Count if the tens digit did not overflow.
E0EE DEC HL Move to the hundreds digit.
E0EF LD A,$01 Carry one into the hundreds digit of the player's score (BCD).
E0F1 ADD A,(HL)
E0F2 DAA
E0F3 LD (HL),A
Process_Entity_Record_Wave_Count E0F4 LD A,($C4DE) Jump to Process_Entity_Record_Decrement_Count if the maximum kill count for this wave is reached.
E0F7 CP $05
E0F9 JP Z,Process_Entity_Record_Decrement_Count
E0FC INC A Increment the wave kill counter.
E0FD LD ($C4DE),A
Process_Entity_Record_Decrement_Count E100 POP AF Restore the entity colour attribute from the stack.
E101 SRL A Extract the entity type to use as a count table index.
E103 SRL A
E105 SRL A
E107 SRL A
E109 LD C,A
E10A LD B,$00 Form a pointer to the entity count entry for this type.
E10C LD HL,$C427
E10F ADD HL,BC
E110 DEC (HL) Decrement the on-screen enemy count for this type.
E111 EX DE,HL Restore the entity list pointer.
E112 PUSH HL Stash the entity list pointer on the stack.
E113 CALL Clear_Colour_Bar_Column Call Clear_Colour_Bar_Column to update the score and wave display.
E116 POP HL Restore the entity list pointer from the stack.
E117 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 E11A DEFB $FF,$00
E11C DEFB $00,$01
E11E DEFB $01,$00
E120 DEFB $00,$FF
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