Routines
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D0F0: Spawn Primary Wave Enemies
Used by the routine at Stage_Next_Wave.
Reads the enemy count and type for the current wave from the definition pointed to by HL, then spawns that many primary wave entities at random valid screen positions by writing records into the entity list at Entity_List_Write_Pointer. Each entity is placed at a random column (1–30) and row (2–22), scaled to pixel coordinates, and drawn to the screen via CC81. If the count is zero the entity list is left empty and the routine returns immediately.
Input
HL Pointer to the wave enemy definition (count byte followed by type byte)
Spawn_Primary_Wave_Enemies D0F0 LD B,(HL) Read the enemy count from the wave definition and store at Wave_Enemy_Count.
D0F1 LD A,B
D0F2 LD ($C423),A
D0F5 INC HL Advance HL to the enemy type byte.
D0F6 LD A,(HL) Read the enemy type parameter from the wave definition.
D0F7 LD ($C424),A Store the enemy type parameter at Wave_Enemy_Type.
D0FA INC HL Advance the wave definition pointer.
D0FB PUSH HL Stash the wave definition pointer on the stack.
D0FC LD HL,($C509) Load the entity list write pointer from *Entity_List_Write_Pointer.
D0FF LD A,B Skip spawning if the wave has no enemies.
D100 AND A
D101 JP Z,Spawn_Primary_Wave_Enemies_Done
For each enemy: write the entity handler, pick a random valid screen position, build the entity record, and draw the sprite.
Spawn_Primary_Wave_Enemies_Loop D104 PUSH BC Stash the enemy count on the stack.
D105 LD DE,$CCCE Load the primary entity handler address Primary_Enemy_Entity_Handler into DE.
D108 LD (HL),E Write the primary entity handler address into the entity list.
D109 INC HL
D10A LD (HL),D
D10B INC HL Advance HL past the handler bytes.
Spawn_Primary_Wave_Enemies_Get_X D10C CALL Generate_Random_Byte Generate a random column via Generate_Random_Byte.
D10F AND %00011111 Mask to columns 0–31.
D111 JR Z,Spawn_Primary_Wave_Enemies_Get_X Retry if the column is at the left or right wall.
D113 CP $1F
D115 JR Z,Spawn_Primary_Wave_Enemies_Get_X
D117 LD B,A Copy the valid column to B.
Spawn_Primary_Wave_Enemies_Get_Y D118 CALL Generate_Random_Byte Generate a random row via Generate_Random_Byte.
D11B AND %00011111 Mask to rows 0–31.
D11D CP $02 Retry if the row is too close to the top or bottom edge.
D11F JR C,Spawn_Primary_Wave_Enemies_Get_Y
D121 CP $17
D123 JR NC,Spawn_Primary_Wave_Enemies_Get_Y
D125 SLA A Scale the row and column to pixel coordinates (multiply by 8).
D127 SLA A
D129 SLA A
D12B SLA B
D12D SLA B
D12F SLA B
D131 LD (HL),A Write the Y pixel to the entity record.
D132 LD ($C4F3),A Cache the Y pixel at Cached_Spawn_Pixels.
D135 INC HL Advance HL to the X slot in the entity record.
D136 LD (HL),B Write the X pixel to the entity record.
D137 LD A,B Copy the X pixel from B into A and cache it at C4F4.
D138 LD ($C4F4),A
D13B INC HL Advance HL to the colour slot.
D13C LD (HL),$07 Write WHITE to the colour and type bytes.
D13E INC HL
D13F LD (HL),$07
D141 DEC HL Step back three bytes to point at the start of the entity record.
D142 DEC HL
D143 DEC HL
D144 EXX Load the entity spawn handler address Entity_Spawn_Handler into alternate HL.
D145 LD HL,$D1C7
D148 EXX
D149 CALL HitTestBounds8AtHL Test whether this position overlaps an existing entity via HitTestBounds8AtHL.
D14C DEC HL Retry with new coordinates if the position is occupied.
D14D DEC HL
D14E DEC HL
D14F JR NC,Spawn_Primary_Wave_Enemies_Get_X
D151 INC HL Advance past the entity record header fields.
D152 INC HL
D153 INC HL
D154 INC HL
D155 LD A,($C424) Copy the wave enemy type from Wave_Enemy_Type into the entity record.
D158 LD (HL),A
D159 INC HL
Build the on-screen pixel address and attribute address from the cached pixel coordinates at Cached_Spawn_Pixels.
D15A EX DE,HL Copy HL to DE (entity record pointer now in DE).
D15B LD HL,$C4F3 Point HL at the cached pixel coordinates at Cached_Spawn_Pixels.
D15E LD A,(HL) Read the Y pixel (row) from the cache.
D15F INC HL Advance HL to the X pixel byte.
D160 LD C,(HL) Read the X pixel (column) from the cache.
D161 LD L,A Move the Y pixel into L for the row term.
D162 LD B,$45 Load the screen address high-byte base 45 into B.
D164 SLA C Shift the X pixel left in C.
D166 RL B Roll the carry into the screen high byte in B.
D168 LD H,$46 Load the second high-byte term 46 into H.
D16A SLA L Shift the Y pixel left in L.
D16C RL H Finish forming the screen address high byte in H.
D16E LD A,(HL) Read the low byte of the pixel data pointer from the table.
D16F INC HL Advance HL to the high byte.
D170 LD H,(HL) Read the high byte of the pixel data pointer.
D171 LD L,A Form the full pixel data pointer in HL (low in L).
D172 LD A,(BC) Read a byte from the built screen address in BC.
D173 OR L Combine the screen low byte with the pixel table low byte.
D174 LD L,A Store the combined screen low byte in L.
D175 EX DE,HL Exchange HL with DE (entity record pointer back in HL).
D176 LD (HL),E Write the screen address into the entity record.
D177 INC HL
D178 LD (HL),D
D179 INC HL Advance HL to the attribute slot.
D17A LD A,D Load the attribute address high byte from D.
D17B RRCA Rotate the attribute page bits toward the low end three times.
D17C RRCA
D17D RRCA
D17E AND %00000011 Mask to the attribute page bits.
D180 OR %01011000 Set the attribute area high byte.
D182 LD D,A Store the attribute address high byte in D.
D183 LD (HL),E Write the attribute address into the entity record.
D184 INC HL
D185 LD (HL),D
D186 DEC HL Step HL back four bytes to the entity origin for drawing.
D187 DEC HL
D188 DEC HL
D189 DEC HL
D18A CALL Draw_Spawned_Entity Call Draw_Spawned_Entity.
D18D DEC HL Step HL to the end-of-record marker position.
D18E LD (HL),$FF Write the record terminator FF after this entity.
D190 INC HL Advance HL for the next list write.
D191 POP BC Restore the enemy count from the stack.
D192 DEC B Decrement the remaining enemies to spawn for this wave.
D193 JP NZ,Spawn_Primary_Wave_Enemies_Loop Loop back to Spawn_Primary_Wave_Enemies_Loop if more enemies remain.
All enemies spawned: write the entity list terminator and return.
Spawn_Primary_Wave_Enemies_Done D196 LD DE,$D1A4 Load Entity_List_Reset into DE.
D199 LD ($C509),HL Store the updated write pointer at Entity_List_Write_Pointer.
D19C LD (HL),E Store the entity list terminator routine address Entity_List_Reset at *HL (low byte then high byte).
D19D INC HL
D19E LD (HL),D
D19F INC HL Advance HL past the stored pointer bytes.
D1A0 LD (HL),$FF Write the terminator byte (FF) to the entity list.
D1A2 POP HL Restore the wave definition pointer from the stack.
D1A3 RET Return.
Inline stub: resets the entity list pointer and returns. Used as the terminal routine address written into the entity list by the spawning routines.
Entity_List_Reset D1A4 LD HL,$6000 Reset the entity list pointer to Entity_List.
D1A7 RET Return.
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