Routines
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29118: Handler: Bullet Collision Effects
Used by the routine at Handler_BulletCollision.
Input
HL Bullet attribute buffer address
Check if this is phase 0 1 or 4. The first section targets only the Pheenix aliens in phase 2 and 3.
Handler_BulletCollisionEffects 29118 LD A,(26353) Jump to BulletCollisionWithMothership if bit 1 of *Phase is not set, so phases
  • 0
  • 1
  • 4
29121 BIT 1,A
29123 JR Z,BulletCollisionWithMothership
Handle the Pheenix aliens in either phase 2 or 3.
29125 LD A,(HL) Load the attribute value from the bullet attribute buffer address.
Check for the Pheenix wing attribute values from either phase.
pheenix-04-blue pheenix-04-magenta
29126 CP 67 Jump to PlayWingHitSound if the attribute value is either INK:MAGENTA, PAPER:BLACK (BRIGHT) or INK:BLUE, PAPER:BLACK (BRIGHT).
29128 JR Z,PlayWingHitSound
29130 CP 65
29132 JR Z,PlayWingHitSound
Return if the bullet is just passing over background.
29134 CP 5 Return if the attribute value is not CYAN.
29136 RET NZ
Play a sound when the Pheenix wings are hit (but not in demo mode).
PlayWingHitSound 29137 LD A,(26355) Return if *Flag_ActiveDemoMode is active.
29140 OR A
29141 RET NZ
29142 LD B,24 Set a counter B for 24 loops.
29144 LD HL,290 Set the initial pitch to 0290.
WingHitSound_Loop 29147 PUSH BC Stash the loop counter and pitch on the stack.
29148 PUSH HL
29149 LD DE,1 Set the sound duration to 0001.
29152 CALL 949 Call BEEPER.
29155 DI Disable interrupts.
29156 POP HL Restore the pitch from the stack.
29157 INC HL Increment the pitch by three.
29158 INC HL
29159 INC HL
29160 POP BC Restore the loop counter from the stack.
29161 DJNZ WingHitSound_Loop Decrease the loop counter by one and loop back to WingHitSound_Loop until all the sound loops are complete.
29163 RET Return.
The only other special bullet handling is when bullets hit the hull of the mothership (only in phase 4).
BulletCollisionWithMothership 29164 CP 4 Return if *Phase is not phase 4.
29166 RET NZ
mothership
Start by handling the final stage of the rotating blue strip.
29167 LD A,(HL) Load the attribute value from the bullet attribute buffer address.
29168 CP 1 Jump to MothershipRotatingStrip if the attribute value is not equal to BLUE.
29170 JR NZ,MothershipRotatingStrip
This part of the ship is BLUE - so it's the rotating strip about to be destroyed (so destroy it).
29172 LD (HL),64 Write INK:BLACK, PAPER:BLACK (BRIGHT) to the bullet/ rotating strip attribute pointer.
29174 JR MothershipHull_ClearUDG Jump to MothershipHull_ClearUDG.
Handle a first hit on the rotating blue strip.
MothershipRotatingStrip 29176 CP 15 Jump to MothershipHull_Stage_02 if the attribute value is not equal to INK:WHITE, PAPER:BLUE.
29178 JR NZ,MothershipHull_Stage_02
This part of the ship is INK:WHITE, PAPER:BLUE - so it's a "fresh" part of the rotating strip.
29180 LD (HL),1 Write BLUE to the bullet/ rotating strip attribute pointer.
29182 JR MothershipHull_DrawLargeDent Jump to MothershipHull_DrawLargeDent.
Handle the second stage of the hull being shot.
MothershipHull_Stage_02 29184 CP 2 Jump to MothershipHull_Stage_01 if the attribute value is not equal to RED.
29186 JR NZ,MothershipHull_Stage_01
This part of the ship is RED so has been hit once already.
29188 PUSH HL Stash the attribute buffer pointer on the stack.
29189 LD A,L Move up one row in the attribute buffer (subtract 32).
29190 SUB 32
29192 LD L,A
29193 LD A,(HL) Load the attribute value from the new attribute buffer address.
29194 CP 16 Jump to MothershipHull_ClearAttribute if the attribute value is not equal to INK:BLACK, PAPER:RED.
29196 JR NZ,MothershipHull_ClearAttribute
29198 LD H,77 Set H to 77 (screen buffer).
Draw the degraded hull partial sprite:
$61EF
Note that the "move to the next UDG graphic data byte" moves backwards not forwards as you'd expect.
29200 LD B,3 Set a line counter in B for 3 (this is a partial graphic from the larger Graphics_MothershipDegradedHull_01).
29202 LD DE,25071 DE=Graphics_MothershipDegradedHull_02.
MothershipHull_DrawLoop 29205 LD A,(DE) Copy the UDG data to the screen buffer.
29206 LD (HL),A
29207 INC H Move down one pixel line in the screen buffer.
29208 DEC DE Move to the next UDG graphic data byte.
29209 DJNZ MothershipHull_DrawLoop Decrease the line counter by one and loop back to MothershipHull_DrawLoop until all 3 lines of the UDG character have been drawn.
Set the attribute value to BLACK now that this section of the hull has been destroyed.
MothershipHull_ClearAttribute 29211 POP HL Restore the attribute buffer pointer from the stack.
29212 LD (HL),0 Write BLACK to *HL.
Point to the "SPACE" (empty UDG graphic) in the ZX Spectrum font to clear the whole UDG area of the hull.
MothershipHull_ClearUDG 29214 LD DE,15616 DE=15616.
29217 JR MothershipHull_DrawUDG Jump to MothershipHull_DrawUDG.
Handle the first stage of the hull being shot.
MothershipHull_Stage_01 29219 CP 16 Jump to MothershipHull_IsAlienShot if the attribute value is not equal to INK:BLACK, PAPER:RED.
29221 JR NZ,MothershipHull_IsAlienShot
29223 LD (HL),2 Write RED to the bullet/ hull attribute pointer.
Draw the degraded hull large sprite:
udg25067_2x4
MothershipHull_DrawLargeDent 29225 LD DE,25067 DE=Graphics_MothershipDegradedHull_01.
MothershipHull_DrawUDG 29228 LD H,72 Set H to 72 (screen buffer).
29230 LD B,8 Set a line counter in B (8 lines in a UDG).
MothershipHull_DrawUDG_Loop 29232 LD A,(DE) Copy the UDG data to the screen buffer.
29233 LD (HL),A
29234 INC DE Move to the next UDG graphic data byte.
29235 INC H Move down one pixel line in the screen buffer.
29236 DJNZ MothershipHull_DrawUDG_Loop Decrease the line counter by one and loop back to MothershipHull_DrawUDG_Loop until all 8 lines of the UDG character have been drawn.
Award 53 points for damaging the hull.
29238 LD A,53 Write 53 to *25902.
29240 LD (25902),A
29243 CALL Handler_Score Call Handler_Score.
29246 CALL PrintScore Call PrintScore.
29249 CALL PrintLives Call PrintLives.
29252 RET Return.
Handle checking if the mothership alien has been shot?
Is this empty space within the mothership graphic?
MothershipHull_IsAlienShot 29253 CP 64 Return if the attribute value is not equal to INK:BLACK, PAPER:BLACK (BRIGHT).
29255 RET NZ
Check the attribute block above where the bullet is positioned.
29256 RES 5,L Clear bit 5 of L to move up one row to the alien attribute position.
Has the bullet reached the mothership alien?
Graphic Attribute Byte Attribute Colour
mothership-alien-01 68 INK:GREEN, PAPER:BLACK (BRIGHT)
66 INK:RED, PAPER:BLACK (BRIGHT)
29258 LD A,(HL) Return if the attribute value at the new position is not equal to INK:RED, PAPER:BLACK (BRIGHT).
29259 CP 66
29261 RET NZ
The bullet has hit the mothership alien.
29262 LD A,1 Write 1 to *MothershipAlienState to mark that the mothership alien has been shot (and so phase 4 is now complete).
29264 LD (26323),A
29267 RET Return.
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