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Routines |
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Used by the routines at Handle_Homing_Enemy, Spawn_Primary_Wave_Enemies, Process_Entity_Record_Fast, Spawn_Wave_Enemies, Handle_Horizontal_Enemy_Entity, Spawn_Horizontal_Wave_Enemies, Pick_Random_Spawn_Position_Y, Process_Cluster_Entity, Process_Player_Tracking_Enemy, Spawn_Tracked_Enemy_Entities, Process_Replacement_Enemy_Entity and Process_Final_Phase_Enemy_Entity.
Produces a single pseudo-random byte by advancing the RNG seed via Advance_RNG_Seed and XOR-mixing its two bytes. HL is preserved. Called throughout the enemy spawning routines to pick random positions and directions.
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| Generate_Random_Byte | D1BF | PUSH HL | Stash HL and advance the RNG seed via Advance_RNG_Seed. | |
| D1C0 | CALL Advance_RNG_Seed | |||
| D1C3 | LD A,L | XOR-mix the seed high and low bytes to produce the random byte. | ||
| D1C4 | XOR H | |||
| D1C5 | POP HL | Restore HL and return. | ||
| D1C6 | RET | |||
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Entity spawn handler stub, invoked by HitTestBounds8AtHL during hit-testing. Stores the entity colour from C and advances the entity pointer.
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| Entity_Spawn_Handler | D1C7 | LD D,B | Initialise the entity colour byte and advance the entity data pointer. | |
| D1C8 | LD (HL),C | |||
| D1C9 | INC HL | |||
| D1CA | RRA | |||
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This entry point is used by the routine at Stage_Next_Wave.
Secondary wave enemy spawn: reads the entity configuration from the wave definition pointed to by HL, then spawns secondary entities (handler CEDF) at random valid pixel positions on the playfield.
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| Spawn_Wave_Enemies_Class2 | D1CB | LD A,(HL) | Read the sprite type byte from the wave definition and store at C425. | |
| D1CC | LD ($C425),A | |||
| D1CF | LD B,A | Copy the sprite type to B, accumulate it into Active_Enemy_Count, and advance the definition pointer. | ||
| D1D0 | LD A,($C41C) | |||
| D1D3 | ADD A,B | |||
| D1D4 | LD ($C41C),A | |||
| D1D7 | INC HL | |||
| D1D8 | LD A,(HL) | Read the direction byte from the definition and store at C426. | ||
| D1D9 | LD ($C426),A | |||
| D1DC | INC HL | |||
| D1DD | LD D,(HL) | Read the speed byte, store at C427; set the initial animation frame pair at Animation_Frame_Pair. | ||
| D1DE | LD A,D | |||
| D1DF | LD ($C427),A | |||
| D1E2 | LD E,$FE | |||
| D1E4 | LD ($C51B),DE | |||
| D1E8 | INC HL | Advance past the definition data and stash the definition pointer; load the entity list write pointer from Entity_List_Write_Pointer. | ||
| D1E9 | PUSH HL | |||
| D1EA | LD HL,($C509) | |||
| D1ED | LD A,B | Skip spawning if the enemy count is zero. | ||
| D1EE | AND A | |||
| D1EF | JP Z,Spawn_Wave_Enemies_Class2_Done | |||
| Spawn_Wave_Enemies_Class2_Loop | D1F2 | PUSH BC | Stash the enemy count and write the secondary entity handler address CEDF to the entity list. | |
| D1F3 | LD DE,$CEDF | |||
| D1F6 | LD (HL),E | |||
| D1F7 | INC HL | |||
| D1F8 | LD (HL),D | |||
| D1F9 | INC HL | |||
| Generate_Random_Byte_0 | D1FA | CALL Generate_Random_Byte | Generate a random direction via Generate_Random_Byte. | |
| D1FD | AND %00000011 | Mask to values 1–3. | ||
| D1FF | JR Z,Generate_Random_Byte_0 | Retry if the direction rolled zero. | ||
| D201 | LD (HL),A | Store the direction and set the initial entity state to 04. | ||
| D202 | INC HL | |||
| D203 | LD (HL),$04 | |||
| D205 | INC HL | |||
| Generate_Random_Byte_1 | D206 | CALL Generate_Random_Byte | Generate a random Y pixel position via Generate_Random_Byte. | |
| D209 | CP $18 | Retry if outside the playfield vertical range (18–A3). | ||
| D20B | JR C,Generate_Random_Byte_1 | |||
| D20D | CP $A4 | |||
| D20F | JR NC,Generate_Random_Byte_1 | |||
| D211 | LD (HL),A | Write the Y position and advance the entity pointer. | ||
| D212 | INC HL | |||
| Generate_Random_Byte_2 | D213 | CALL Generate_Random_Byte | Generate a random X pixel position via Generate_Random_Byte. | |
| D216 | CP $08 | Retry if outside the playfield horizontal range (08–EE). | ||
| D218 | JR C,Generate_Random_Byte_2 | |||
| D21A | CP $EF | |||
| D21C | JR NC,Generate_Random_Byte_2 | |||
| D21E | LD (HL),A | Write the X position and the entity dimensions (0C × 09). | ||
| D21F | INC HL | |||
| D220 | LD (HL),$0C | |||
| D222 | INC HL | |||
| D223 | LD (HL),$09 | |||
| D225 | DEC HL | Step back to the entity record origin and load the spawn handler Entity_Spawn_Handler into alternate HL. | ||
| D226 | DEC HL | |||
| D227 | DEC HL | |||
| D228 | EXX | |||
| D229 | LD HL,$D1C7 | |||
| D22C | EXX | |||
| D22D | CALL HitTestBounds8AtHL | Test whether this position overlaps an existing entity via HitTestBounds8AtHL. | ||
| D230 | JR C,Spawn_Wave_Enemies_Class2_Accept | Jump to Spawn_Wave_Enemies_Class2_Accept if the position is clear. | ||
| D232 | DEC HL | Step back and retry with a new X position. | ||
| D233 | DEC HL | |||
| D234 | DEC HL | |||
| D235 | JR Generate_Random_Byte_1 | |||
| Spawn_Wave_Enemies_Class2_Accept | D237 | INC HL | Advance past the entity record and write the FF end-of-record marker. | |
| D238 | LD (HL),$FF | |||
| D23A | INC HL | |||
| D23B | POP BC | Restore the enemy count and loop for the next secondary enemy. | ||
| D23C | DJNZ Spawn_Wave_Enemies_Class2_Loop | |||
| Spawn_Wave_Enemies_Class2_Done | D23E | LD DE,$D1A4 | Write the entity list return-routine address and the FF sentinel; store the updated entity list write pointer at Entity_List_Write_Pointer. | |
| D241 | LD ($C509),HL | |||
| D244 | LD (HL),E | |||
| D245 | INC HL | |||
| D246 | LD (HL),D | |||
| D247 | INC HL | |||
| D248 | LD (HL),$FF | |||
| D24A | POP HL | Restore the wave definition pointer and return. | ||
| D24B | RET | |||
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