| Routines

28143: Check whether a shield has been hit

Used by the routine at 28102. Returns with the carry flag set if a shield was hit (either by a catapult pellet or by ERIC while jumping).
Input
D | Target y-coordinate
E | 128 + target x-coordinate
28143 | LD A,(32746) | 32746 holds the game mode indicator
28146 | RRCA | Are the shields hittable at the moment?
28147 | RET NC | Return if not (it's either demo mode, or ERIC's looking for the safe combination)
28148 | RRCA | Now bit 7 of C is reset if we're in 'flash the shields' mode, or set if in 'unflash the shields' mode
28149 | LD C,A
28150 | LD B,10 | 100 points for hitting a shield on the top floor
28152 | LD A,D | A=y-coordinate of the potential target
28153 | CP 154 | This is the y-coordinate of the shields on the top floor
28155 | JR Z,28171 | Jump if the pellet or ERIC's hand is at shield-height on the top floor
28157 | CP 160 | This is the y-coordinate of the shields on the middle floor
28159 | LD B,20 | 200 points for hitting a shield on the middle floor
28161 | JR Z,28171 | Jump if the pellet or ERIC's hand is at shield-height on the middle floor
28163 | LD B,40 | 400 points for hitting a shield on the bottom floor
28165 | CP 166 | This is the y-coordinate of the shields on the bottom floor
28167 | JR Z,28171 | Jump if the pellet or ERIC's hand is at shield-height on the bottom floor
28169 | AND A | Reset the carry flag to indicate that no shield was hit
28170 | RET |
The pellet or ERIC's hand is at the right height to hit a shield. Is it at the right x-coordinate?
28171 | CALL 62674 | Is the potential target on-screen?
28174 | CCF |
28175 | RET NC | Return with the carry flag reset if not
28176 | LD A,(DE) | A=attribute of the potential target
28177 | AND 56 | Return if the potential target is drawn in black paper or black ink (which is normally true only if it's not a shield, but is also true if a speech bubble has been drawn over a shield; in this case, the routine exits here, which is a bug)
28179 | RET Z
28180 | LD A,(DE)
28181 | AND 7
28183 | RET Z
28184 | LD A,(DE) | A=attribute of the shield
28185 | XOR C | Check whether we should make the shields flash or not flash, and return unless the flash status of the shield should be toggled
28186 | RLCA
28187 | RET C
28188 | LD A,(DE) | A=attribute of the shield
28189 | XOR 128 | Toggle the FLASH status of the shield
28191 | LD (DE),A | Insert the new attribute byte into the skool graphic data
28192 | LD (HL),A | Apply the new attribute on-screen
28193 | LD A,B | A=10 (top floor), 20 (middle) or 40 (bottom)
28194 | CALL 27389 | Add 100, 200 or 400 to the score and print it
28197 | CALL 58604 | Play the 'hit a shield' sound effect
28200 | LD HL,32747 | 32747 holds the shield counter
28203 | DEC (HL) | One more shield hit
28204 | SCF | Set the carry flag to indicate that a shield was hit
28205 | RET NZ | Return unless the last shield was hit
28206 | CALL 63668 | All the shields have been hit; take appropriate action
28209 | SCF | Set the carry flag to indicate that a shield was hit
28210 | RET |