| Routines

25420: Control a banknote

Used by the command list at 64888. Calculates and sets the banknote's next animatory state and location. If the banknote is far enough off-screen to the left or right, it will be moved to a location just off-screen to the left.
Input
H | 228 or 229 (banknote)
25420 | LD A,(32745) | 32745 holds Sam's object inventory
25423 | RLCA | Has Sam got the hook (bit 6 set)?
25424 | RLCA
25425 | JR NC,25434 | Jump if not
Sam's got the hook; we bring this banknote out of service so that its character buffer is available for use by the hook when it's thrown. However, the banknote is not removed from view, which is a bug.
25427 | CALL 59848 | Update the SRB for the banknote's current animatory state and location
25430 | CALL 63409 | Change the banknote's primary command routine address to 25433 (below)
25433 | RET |
This entry point is used by the command list at 64886.
25434 | LD L,10 | Collect byte 10 of the banknote's buffer
25436 | LD A,(HL)
25437 | AND A | Reset the zero flag if Sam has just landed on this banknote
25438 | LD (HL),0 | Set byte 10 to zero
25440 | JR NZ,25461 | Jump if Sam has just landed on this banknote
First we check whether the banknote is far off-screen to the left or right.
25442 | LD L,1 | Point HL at byte 1 of the banknote's buffer
25444 | LD A,(32766) | A=X (the x-coordinate of the leftmost column of the play area on screen)
25447 | SUB 12 | Is X=0 or 8?
25449 | JR C,25454 | Jump if so
25451 | CP (HL) | Is the banknote's x-coordinate greater than X-12?
25452 | JR NC,25461 | Jump if not
25454 | ADD A,60 | A=X+48
25456 | JR C,25477 | Jump if X=0, 8, 208, 216 or 224
25458 | CP (HL) | Is the banknote's x-coordinate greater than X+48?
25459 | JR NC,25477 | Jump if not
The banknote is off-screen to the left by at least 12 x-coordinates, or it's off-screen to the right by at least 17 x-coordinates, or it's just been landed on by Sam. Time to reinitialise its animatory state and location.
25461 | CALL 59848 | Update the SRB for the banknote's current animatory state and location
25464 | LD D,34 | Initialise the banknote's y-coordinate to 34
25466 | LD A,(32766) | A=X (the x-coordinate of the leftmost column of the play area on screen)
25469 | SUB 11 | Is X>8?
25471 | JR NC,25474 | Jump if so
25473 | SBC A,A | A=255
25474 | LD E,A | E=255 (if X<=8) or X-11
25475 | JR 25480 |
The banknote is on-screen or not far off it. Now we calculate the banknote's next animatory state and location.
25477 | CALL 59848 | Update the SRB for the banknote's current animatory state and location
25480 | PUSH AF | Save the banknote's current animatory state briefly
25481 | CALL 61823 | Get a random number in A
25484 | LD C,A | Copy it to C
25485 | AND 136 | Keep only bits 3 and 7
25487 | ADD A,62 | B=62, 70, 190, or 198 (banknote animatory states)
25489 | LD B,A
25490 | POP AF | Restore the banknote's current animatory state to A
25491 | CP B | Is it equal to B?
25492 | JR Z,25480 | Jump back to generate another animatory state if so
At this point B holds the banknote's next animatory state. Now we calculate its next location.
25494 | LD A,B | A=banknote's next animatory state
25495 | PUSH AF | Save this briefly
25496 | CALL 60164 | Set the carry flag if the banknote is above the road (as opposed to the sidewalk)
25499 | ADC A,45 | A=45 if the banknote is above the sidewalk, or 46 if it's above the road
25501 | SUB E
25502 | SUB D | Subtract the banknote's current y-coordinate (32-35); now A=11+G, where G (-1<=G<=3) is the height of the banknote above the ground
25503 | LD B,A | Multiply this value by 5 and add 1 (A=51, 56, 61, 66, or 71)
25504 | ADD A,A
25505 | ADD A,A
25506 | ADD A,B
25507 | INC A
25508 | PUSH HL | Save the banknote's character number
25509 | LD L,A | Point HL at the entry in the banknote animation table at 25395 that corresponds to the banknote's height above the ground
25510 | LD H,99
25512 | LD A,C | A=random number generated earlier
25513 | LD BC,1283 | B=5 (number of bytes in the entry), C=3
25516 | CP (HL) | Find the first byte in the entry that is greater than A
25517 | JR C,25522
25519 | INC HL
25520 | DJNZ 25516
25522 | LD A,B | A=0-5
25523 | CP C | Is A<3?
25524 | JR C,25528 | Jump if so
25526 | INC E | Otherwise increment the banknote's x-coordinate
25527 | SUB C | A=0-2
25528 | ADD A,A | A=0, 2 or 4
25529 | JR Z,25532 | Jump if A=0
25531 | SUB C | A=-1 or 1
25532 | ADD A,D | Add -1, 0 or 1 to the banknote's current y-coordinate
25533 | LD D,A
25534 | POP HL | Restore the banknote's character number to H
25535 | POP AF | Restore the banknote's next animatory state to A
25536 | JP 59861 | Update the banknote's animatory state and location and update the SRB