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FA39: Control water fired from the pistol (2)
Continues from F9AB. On entry the carry flag is set if the water is travelling to the right. In the following, 'water' may refer to either water or sherry.
A Water's current x-coordinate
B Water's new animatory state
C x-coordinate increment (-2, -1 or 0)
D Water's new y-coordinate
H 0xD6 (water)
FA39 JR NC,$FA3D Jump if the water is travelling to the left
FA3B SUB C Add 0, 1 or 2 to the water's current x-coordinate
FA3C SUB C Do the same again to compensate for the ADD A,C instruction below
FA3D ADD A,C Now A=new x-coordinate for the water
FA3E LD E,A Copy this to E
FA3F CP $BF Reset the carry flag if the water has hit the far left wall of the boys' skool or the far right wall of the girls' skool
FA41 LD A,B Transfer the water's new animatory state to A
FA42 JP C,$6130 Update the water's animatory state and location and update the SRB (if the water hasn't hit one of the far walls, i.e. it's still entirely on-screen)
FA45 LD L,$12 Otherwise remove the uninterruptible subcommand routine address (F9D8) from bytes 0x11 and 0x12 of the water's buffer
FA47 LD (HL),$00
FA49 JP $74D6 Place the water out of sight
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