Routines
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25118: Control the sniper while active
The address of this interruptible subcommand routine is placed into bytes 14 and 15 of the sniper's buffer by the routine at 25307. It controls the sniper from the moment he appears until he hides again.
Input
H 227 (sniper)
25118 LD L,2 A=sniper's y-coordinate
25120 LD A,(HL)
25121 LD L,17 Point HL at byte 17 of the sniper's buffer
25123 INC (HL) Is it zero (meaning the sniper has not fired recently)?
25124 DEC (HL)
25125 JR Z,25128 Jump if so
25127 DEC (HL) Otherwise decrement byte 17
25128 DEC L L=16
25129 CP 50 The sniper's y-coordinate is 50 when he's inactive
25131 JR NZ,25168 Jump if the sniper is currently active
The sniper is currently inactive.
25133 DEC (HL) Decrement byte 16 of the sniper's buffer
25134 JP Z,62084 Terminate this subcommand if byte 16 is now 0
25137 CALL 26328 Is the sniper on screen at least 8 x-coordinates away from Sam?
25140 NOP
25141 JP NZ,62084 Terminate this subcommand if not
25144 INC L Point HL at byte 2 of the sniper's buffer
25145 LD (HL),37 Set the sniper's y-coordinate to 37 (out of sight, but ready to emerge)
25147 LD A,(58881) A=Sam's x-coordinate
25150 DEC L L=1
25151 SUB (HL) Subtract the sniper's x-coordinate
25152 CCF Compute the appropriate animatory state for the sniper: 54 if he's to the right of Sam, 182 if he's to the left
25153 LD A,108
25155 RRA
25156 DEC HL Set the sniper's animatory state
25157 LD (HL),A
This entry point is used by the routine at 28646.
25158 LD L,2 Collect the sniper's x- and y-coordinates in DE
25160 LD D,(HL)
25161 DEC HL
25162 LD E,(HL)
25163 DEC HL A=sniper's animatory state
25164 LD A,(HL)
25165 JP 26224 Update the sniper's sprite tile references
The sniper is currently active (his y-coordinate is 34-37).
25168 LD A,(57014) Collect the sprite tile reference for tile 7 of animatory states 54/182; this will be 235 if the sniper is firing, or 0, 110, 111 or 113 otherwise
25171 CP H Is the sniper firing?
25172 JP NC,28646 If so, make the firing sound effect
25175 LD A,(32767) A=y-coordinate of the topmost row of the play area on screen
25178 CP 20 Is the sidewalk on screen?
25180 JR NZ,25193 If not, deactivate the sniper and terminate this subcommand
25182 DEC (HL) Decrement byte 16 of the sniper's buffer
25183 JR NZ,25210 Jump unless byte 16 is now zero
Byte 16 of the sniper's buffer has been decremented to zero. The apparent intention here is to make the sniper duck out of sight and terminate this subcommand; however, if the sniper is not already out of sight, he will duck briefly but remain in view, and byte 16 will be decremented to 255 on the next pass through this routine. This is a bug.
25185 CALL 59848 Update the SRB for the sniper's current animatory state and location
25188 LD A,D A=sniper's y-coordinate
25189 CP 37 Is the sniper currently out of sight?
25191 JR NZ,25202 Jump if not to make him duck
25193 LD L,15 Remove the address of this routine from bytes 14 and 15 of the sniper's buffer
25195 LD (HL),0
25197 LD L,2 Set the sniper's y-coordinate to 50 (inactive)
25199 LD (HL),50
25201 RET
The sniper is in the process of ducking.
25202 INC D D=sniper's next y-coordinate (35-37)
25203 LD L,0 Point HL at byte 0 of the sniper's buffer
25205 LD A,(HL) A=sniper's animatory state
25206 AND A Reset the carry flag to indicate that the sniper is not firing
25207 JP 26224 Update the sniper's sprite tile references
Byte 16 of the sniper's buffer is not zero.
25210 CALL 26328 Compare the sniper's coordinates with Sam's
25213 JR Z,25227 Jump if the sniper is on screen and at least 8 x-coordinates away from Sam
25215 JR NC,25193 Terminate this subcommand if the sniper if off screen
25217 CALL 59848 Update the SRB for the sniper's current animatory state and location
25220 LD A,D A=sniper's y-coordinate
25221 CP 37 Has the sniper already ducked out of sight?
25223 JR NZ,25202 Jump if not to make the sniper continue ducking
25225 JR 25197 Deactivate the sniper
The sniper is on screen and at least 8 x-coordinates away from Sam. If he's already popped his head out far enough (his y-coordinate is 34 or 35), he can consider shooting; otherwise he'll need to emerge a little further first.
25227 LD L,2 Point HL at byte 2 of the sniper's buffer
25229 LD A,(HL) A=sniper's y-coordinate
25230 CP 36 Is at least half of the sniper visible?
25232 JR C,25240 Jump if so
25234 CALL 59848 Update the SRB for the sniper's current animatory state and location
25237 DEC D D=sniper's next y-coordinate (35 or 36)
25238 JR 25206 Jump back to update the sniper's sprite tile references
At least half of the sniper is visible (his y-coordinate is 34 or 35), which means he can shoot.
25240 LD L,16 Collect byte 16 of the sniper's buffer
25242 LD A,(HL)
25243 AND 3 Is bit 0 or bit 1 set?
25245 JR NZ,25263 Jump if so
25247 CALL 61823 Get a random number in A
25250 CP 160 Should the sniper consider shooting?
25252 JR C,25263 Jump if so (5 times out of 8)
25254 CALL 59848 Update the SRB for the sniper's current animatory state and location
25257 LD A,D A=sniper's y-coordinate (34 or 35)
25258 XOR 1 Toggle between 34 and 35
25260 LD D,A D=sniper's next y-coordinate (35 or 34)
25261 JR 25203 Jump back to update the sniper's sprite tile references
The sniper will consider shooting.
25263 LD A,(58884) A=Sam's z-coordinate
25266 RRCA Is Sam indoors?
25267 RET C Return if so
25268 LD A,(32764) Collect Sam's status flags from 32764
25271 AND 129 Is Sam falling from a building or being carried?
25273 RET NZ Return if so
25274 LD L,17 Collect byte 17 of the sniper's buffer
25276 LD A,(HL)
25277 AND A Has the sniper fired recently?
25278 RET NZ Return if so
25279 CALL 61823 Get a random number in A
25282 CP 84 Should the sniper continue to consider shooting?
25284 RET NC Return if not (21 times out of 64)
25285 LD DE,32706 Point DE at the third byte of bullet buffer 1 (at 32704)
25288 LD A,(DE) Pick this up in A
25289 AND A Is bullet buffer 1 in use?
25290 JR Z,25297 Jump if not
25292 LD E,198 Point DE at the third byte of bullet buffer 2 (at 32708)
25294 LD A,(DE) Pick this up in A
25295 AND A Is bullet buffer 2 in use?
25296 RET NZ Return if so
The sniper has decided to shoot, and a bullet buffer is available.
25297 LD (HL),12 Place 12 into byte 17 of the sniper's buffer (indicating that he's just fired)
25299 CALL 59848 Update the SRB for the sniper's current animatory state and location
25302 SCF Set the carry flag to indicate that the sniper is firing
25303 JP 26224 Update the sniper's sprite tile references and initialise a bullet
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