Routines
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31154: Handler: Alien Explosions
Used by the routines at TitleScreen and StartGame.
Handler_AlienExplosions 31154 LD A,(26261) Return if bit 0 of *Bullet_RateLimiter is not set.
31157 AND %00000001
31159 RET Z
31160 LD HL,26325 HL=Table_AlienExplosions.
31163 LD B,6 Set a counter in B for checking 6 explosion slots.
AlienExplosions_Loop 31165 LD A,(HL) Jump to AlienExplosions_IsActive if this explosion slot is already active.
31166 OR A
31167 JR NZ,AlienExplosions_IsActive
31169 PUSH BC Stash the explosion slot counter on the stack.
31170 LD B,200 Set a delay loop counter in B of 200 iterations.
AlienExplosions_DelayLoop 31172 DJNZ AlienExplosions_DelayLoop Decrease the delay loop counter by one and loop back to AlienExplosions_DelayLoop until the counter is zero.
31174 POP BC Restore the explosion slot counter from the stack.
31175 JP AlienExplosions_NextSlot Jump to AlienExplosions_NextSlot.
Process the active explosion.
AlienExplosions_IsActive 31178 PUSH AF Stash AF, BC and HL on the stack.
31179 PUSH BC
31180 PUSH HL
Play a sound when the explosion is active (but not in demo mode).
31181 LD A,(26355) Jump to AlienExplosions_UpdatePosition if *Flag_ActiveDemoMode is active.
31184 OR A
31185 JR NZ,AlienExplosions_UpdatePosition
Play the explosion sound effect based on the current phase.
31187 LD A,(26353) Jump to AlienExplosions_Sound_02 if bit 1 of *Phase is not zero.
31190 AND %00000010
31192 JR Z,AlienExplosions_Sound_02
Play explosion sound 1.
31194 LD A,(HL) DE=*HL*8.
31195 ADD A,A
31196 ADD A,A
31197 ADD A,A
31198 LD E,A
31199 LD D,0
31201 LD HL,242 HL=0242+DE.
31204 ADD HL,DE
31205 LD B,3 B=3.
AlienExplosions_Sound_01 31207 PUSH BC Stash BC and HL on the stack.
31208 PUSH HL
31209 LD DE,2 DE=0002.
31212 CALL 949 Call BEEPER.
31215 DI Disable interrupts.
31216 POP HL Restore HL from the stack.
31217 INC HL Increment HL by two.
31218 INC HL
31219 POP BC Restore BC from the stack.
31220 DJNZ AlienExplosions_Sound_01 Decrease counter by one and loop back to AlienExplosions_Sound_01 until counter is zero.
31222 JR AlienExplosions_UpdatePosition Jump to AlienExplosions_UpdatePosition.
Play explosion sound 2.
AlienExplosions_Sound_02 31224 LD A,(HL) Jump to AlienExplosions_UpdatePosition if the explosion type is not 1.
31225 CP 1
31227 JR NZ,AlienExplosions_UpdatePosition
31229 LD B,18 Set a counter in B for 18 explosion sound loops.
31231 LD HL,100 Set the initial pitch to 0100.
AlienExplosions_Sound_02_Loop 31234 PUSH BC Stash the explosion sound loops counter and pitch on the stack.
31235 PUSH HL
31236 LD A,100 Calculate the delay counter: 100 - (B × 2).
31238 SUB B
31239 SUB B
31240 LD B,A
31241 LD A,16 Enable the speaker (bit 4).
31243 DI Disable interrupts.
AlienExplosions_Sound_02_DelayLoop 31244 OUT (254),A Decrease the delay counter by one and loop back to AlienExplosions_Sound_02_DelayLoop until the delay counter is zero.
31246 DJNZ AlienExplosions_Sound_02_DelayLoop
31248 LD DE,1 Set the sound duration to 0001.
31251 CALL 949 Call BEEPER.
31254 DI Disable interrupts.
31255 POP HL Restore the pitch from the stack.
31256 LD BC,8 Increase the pitch by 0008.
31259 ADD HL,BC
31260 POP BC Restore the explosion sound loops counter from the stack.
31261 DJNZ AlienExplosions_Sound_02_Loop Decrease the explosion sound loops counter by one and loop back to AlienExplosions_Sound_02_Loop until the explosion sound has finished playing.
Update the explosion position and check for scoring.
AlienExplosions_UpdatePosition 31263 POP HL Restore HL, BC and AF from the stack.
31264 POP BC
31265 POP AF
31266 PUSH BC Stash BC and HL on the stack.
31267 PUSH HL
31268 INC HL Increment HL by one.
31269 LD E,(HL) E=*HL.
31270 INC HL Increment HL by one.
31271 LD D,(HL) D=*HL.
31272 LD C,A C=A.
31273 LD A,(26353) A=*Phase.
31276 AND %00000010 Keep only bit 1.
31278 LD A,C A=C.
31279 JR NZ,Handler_AlienExplosions_6 Jump to Handler_AlienExplosions_6 if bit 1 of *Phase was set.
31281 CP 1 Jump to Handler_AlienExplosions_0 if A is not equal to 1.
31283 JR NZ,Handler_AlienExplosions_0
31285 PUSH DE Stash DE and AF on the stack.
31286 PUSH AF
31287 EX DE,HL Exchange the DE and HL registers.
31288 CALL ConvertAttributeToScreenBufferAddress Call ConvertAttributeToScreenBufferAddress.
31291 EX DE,HL Exchange the DE and HL registers.
31292 CALL ClearSpriteArea Call ClearSpriteArea.
31295 POP AF Restore AF and DE from the stack.
31296 POP DE
Handler_AlienExplosions_0 31297 CP 4 Jump to Handler_AlienExplosions_2 if A is not equal to 4.
31299 JR NZ,Handler_AlienExplosions_2
31301 PUSH DE Stash DE and AF on the stack.
31302 PUSH AF
31303 LD HL,25901 HL=25901.
31306 LD (HL),56 Write 56 to *HL.
31308 LD A,D Jump to Handler_AlienExplosions_1 if D is equal to 90.
31309 CP 90
31311 JR Z,Handler_AlienExplosions_1
31313 LD (HL),50 Write 50 to *HL.
31315 INC HL Increment HL by one.
31316 LD (HL),53 Write 53 to *HL.
Handler_AlienExplosions_1 31318 CALL Handler_Score Call Handler_Score.
31321 CALL PrintScore Call PrintScore.
31324 CALL PrintLives Call PrintLives.
31327 POP AF Restore AF and DE from the stack.
31328 POP DE
Handler_AlienExplosions_2 31329 CP 7 Compare A with 7.
31331 LD BC,836 BC=836.
31334 JR C,Handler_AlienExplosions_3 Jump to Handler_AlienExplosions_3 if A is less than 7.
31336 LD HL,25909 HL=Table_ExplosionUDGs_03.
31339 CP 9 Jump to Handler_AlienExplosions_5 if A is less than 9.
31341 JR C,Handler_AlienExplosions_5
31343 LD C,3 C=3.
31345 JR Handler_AlienExplosions_5 Jump to Handler_AlienExplosions_5.
Handler_AlienExplosions_3 31347 INC C Increment C by one.
31348 CP 4 Jump to Handler_AlienExplosions_4 if A is less than 4.
31350 JR C,Handler_AlienExplosions_4
31352 LD HL,25906 HL=Table_ExplosionUDGs_02.
31355 JR Handler_AlienExplosions_5 Jump to Handler_AlienExplosions_5.
Handler_AlienExplosions_4 31357 LD C,71 C=71.
31359 LD HL,25903 HL=Table_ExplosionUDGs_01.
Handler_AlienExplosions_5 31362 PUSH DE Stash DE on the stack.
31363 EX DE,HL Exchange the DE and HL registers.
31364 CALL ConvertAttributeToScreenBufferAddress Call ConvertAttributeToScreenBufferAddress.
31367 PUSH HL Stash HL and BC on the stack.
31368 PUSH BC
31369 LD BC,20672 HL-=20672.
31372 AND A
31373 SBC HL,BC
31375 POP BC Restore BC and HL from the stack.
31376 POP HL
31377 EX DE,HL Exchange the DE and HL registers.
31378 CALL C,CustomFont_PrintString Call CustomFont_PrintString if A is less than 0.
31381 POP DE Restore DE from the stack.
31382 JP Handler_AlienExplosions_14 Jump to Handler_AlienExplosions_14.
Handler_AlienExplosions_6 31385 CP 1 Jump to Handler_AlienExplosions_7 if A is not equal to 1.
31387 JR NZ,Handler_AlienExplosions_7
31389 PUSH DE Stash DE and AF on the stack.
31390 PUSH AF
31391 EX DE,HL Exchange the DE and HL registers.
31392 CALL ConvertAttributeToScreenBufferAddress Call ConvertAttributeToScreenBufferAddress.
31395 EX DE,HL Exchange the DE and HL registers.
31396 CALL ClearSpriteArea Call ClearSpriteArea.
31399 POP AF Restore AF and DE from the stack.
31400 POP DE
31401 INC DE Increment DE by one.
31402 LD (DE),A Write A to *DE.
31403 DEC DE Decrease DE by one.
31404 JR Handler_AlienExplosions_10 Jump to Handler_AlienExplosions_10.
Handler_AlienExplosions_7 31406 CP 2 Jump to Handler_AlienExplosions_10 if A is not equal to 2.
31408 JR NZ,Handler_AlienExplosions_10
31410 PUSH AF Stash AF and DE on the stack.
31411 PUSH DE
31412 LD HL,25900 HL=25900.
31415 PUSH HL Stash HL on the stack.
31416 LD (HL),49 Write 49 to *HL.
31418 LD A,(26257) Jump to Handler_AlienExplosions_9 if *26257 is zero.
31421 OR A
31422 JR Z,Handler_AlienExplosions_9
31424 LD A,D Jump to Handler_AlienExplosions_8 if D is less than 89.
31425 CP 89
31427 JR C,Handler_AlienExplosions_8
31429 LD (HL),50 Write 50 to *HL.
31431 JR Z,Handler_AlienExplosions_9 Jump to Handler_AlienExplosions_9 if A is equal to 89.
Handler_AlienExplosions_8 31433 INC HL Increment HL by one.
31434 LD (HL),53 Write 53 to *HL.
Handler_AlienExplosions_9 31436 EX DE,HL Exchange the DE and HL registers.
31437 CALL ConvertAttributeToScreenBufferAddress Call ConvertAttributeToScreenBufferAddress.
31440 PUSH HL Stash HL on the stack.
31441 LD BC,20672 HL-=20672.
31444 AND A
31445 SBC HL,BC
31447 POP HL Restore HL from the stack.
31448 EX DE,HL Exchange the DE and HL registers.
31449 POP HL Restore HL from the stack.
31450 LD BC,837 BC=837.
31453 CALL C,Configurable_PrintString Call Configurable_PrintString if A is less than 0.
31456 CALL Handler_Score Call Handler_Score.
31459 CALL PrintScore Call PrintScore.
31462 CALL PrintLives Call PrintLives.
31465 POP DE Restore DE and AF from the stack.
31466 POP AF
Handler_AlienExplosions_10 31467 PUSH DE Stash DE on the stack.
31468 LD C,A C=A.
31469 LD A,E A=E.
31470 INC A Increment A by one.
31471 AND %00011111 Keep only bits 0-4.
31473 SUB C A-=C.
31474 JR C,Handler_AlienExplosions_12 Jump to Handler_AlienExplosions_12 if A is less than A.
31476 PUSH BC Stash BC and AF on the stack.
31477 PUSH AF
31478 LD A,E E-=C.
31479 SUB C
31480 LD E,A
31481 INC E Increment E by one.
31482 CALL Handler_Mask Call Handler_Mask.
31485 DEC E Decrease E by one.
31486 POP AF Restore AF from the stack.
31487 JR Z,Handler_AlienExplosions_11 Jump to Handler_AlienExplosions_11 until E is zero.
31489 POP BC Restore BC from the stack.
31490 PUSH BC Stash BC on the stack.
31491 LD A,C Jump to Handler_AlienExplosions_11 if C is equal to 16.
31492 CP 16
31494 JR Z,Handler_AlienExplosions_11
31496 CALL Handler_EggsplosionLeft Call Handler_EggsplosionLeft.
Handler_AlienExplosions_11 31499 POP BC Restore BC and DE from the stack.
Handler_AlienExplosions_12 31500 POP DE
31501 PUSH DE Stash DE on the stack.
31502 INC E Increment E by one.
31503 LD A,E A=E.
31504 AND %00011111 Keep only bits 0-4.
31506 ADD A,C A+=C.
31507 CP 32 Jump to Handler_AlienExplosions_13 if A is greater than or equal to 32.
31509 JR NC,Handler_AlienExplosions_13
31511 PUSH BC Stash BC on the stack.
31512 CP 31 Compare A with 31.
31514 PUSH AF Stash AF on the stack.
31515 LD A,E E+=C.
31516 ADD A,C
31517 LD E,A
31518 DEC DE Decrease DE by one.
31519 CALL Handler_Mask Call Handler_Mask.
31522 INC DE Increment DE by one.
31523 POP AF Restore AF and BC from the stack.
31524 POP BC
31525 JR Z,Handler_AlienExplosions_13 Jump to Handler_AlienExplosions_13 if ??? is zero.
31527 LD A,C Jump to Handler_AlienExplosions_13 if C is equal to 16.
31528 CP 16
31530 JR Z,Handler_AlienExplosions_13
31532 CALL Handler_EggsplosionRight Call Handler_EggsplosionRight.
Handler_AlienExplosions_13 31535 POP DE Restore DE and HL from the stack.
Handler_AlienExplosions_14 31536 POP HL
31537 INC (HL) Increment *HL by one.
The number of frames the explosion persists for varies between the phases, presumably because some phases allow the ship to make "quick shots" and the number of slots may be at risk when the player can fire more rapidly.
31538 LD A,(26353) A=*Phase.
31541 AND %00000010 Keep only bit 1.
31543 LD A,11 Set the frame limit in A to 11 frames.
31545 JR Z,AlienExplosions_CheckComplete Jump to AlienExplosions_CheckComplete if bit 1 of *Phase was not set.
31547 LD A,17 Set the frame limit in A to 17 frames.
AlienExplosions_CheckComplete 31549 CP (HL) Jump to AlienExplosions_Continue if *HL is not equal to the frame limit.
31550 JR NZ,AlienExplosions_Continue
31552 LD (HL),0 Clear the current explosion slot (set to 0).
31554 PUSH HL Stash the explosion slot pointer on the stack.
31555 EX DE,HL Exchange the DE and HL registers.
31556 CALL ConvertAttributeToScreenBufferAddress Call ConvertAttributeToScreenBufferAddress.
31559 PUSH HL Stash HL on the stack.
31560 LD BC,20672 HL-=20672.
31563 AND A
31564 SBC HL,BC
31566 POP HL Restore HL from the stack.
31567 EX DE,HL Exchange the DE and HL registers.
Prints
31568 LD HL,16155 HL=16155.
31571 LD BC,768 BC=0768.
31574 CALL C,SpectrumFont_PrintString Call SpectrumFont_PrintString if ?? is less than 0.
31577 LD HL,26239 Decrease *AlienCount by one.
31580 DEC (HL)
31581 POP HL Restore the explosion slot pointer from the stack.
AlienExplosions_Continue 31582 POP BC Restore the explosion slot counter from the stack.
Move to the next explosion slot.
AlienExplosions_NextSlot 31583 INC HL Move the explosion slot pointer to the next explosion slot.
31584 INC HL
31585 INC HL
31586 DEC B Decrease the explosion slot counter by one.
31587 JP NZ,AlienExplosions_Loop Jump back to AlienExplosions_Loop until all explosion slots have been processed.
31590 RET Return.
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