Data
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8421: Left-right movement table
 Used by the routine at 8ED4. The entries in this table are used to map the existing value (V) of Willy's direction and movement flags at 85D0 to a new value (V'), depending on the direction Willy is facing and how he is moving or being moved (by 'left' and 'right' keypresses and joystick input, or by a conveyor, or by an urge to visit the toilet). One of the first four entries is used when Willy is not moving. 8421 DEFB \$00 V=0 (facing right, no movement) + no movement: V'=0 (no change) 8422 DEFB \$01 V=1 (facing left, no movement) + no movement: V'=1 (no change) 8423 DEFB \$00 V=2 (facing right, moving) + no movement: V'=0 (facing right, no movement) (i.e. stop) 8424 DEFB \$01 V=3 (facing left, moving) + no movement: V'=1 (facing left, no movement) (i.e. stop) One of the next four entries is used when Willy is moving left. 8425 DEFB \$01 V=0 (facing right, no movement) + move left: V'=1 (facing left, no movement) (i.e. turn around) 8426 DEFB \$03 V=1 (facing left, no movement) + move left: V'=3 (facing left, moving) 8427 DEFB \$01 V=2 (facing right, moving) + move left: V'=1 (facing left, no movement) (i.e. turn around) 8428 DEFB \$03 V=3 (facing left, moving) + move left: V'=3 (no change) One of the next four entries is used when Willy is moving right. 8429 DEFB \$02 V=0 (facing right, no movement) + move right: V'=2 (facing right, moving) 842A DEFB \$00 V=1 (facing left, no movement) + move right: V'=0 (facing right, no movement) (i.e. turn around) 842B DEFB \$02 V=2 (facing right, moving) + move right: V'=2 (no change) 842C DEFB \$00 V=3 (facing left, moving) + move right: V'=0 (facing right, no movement) (i.e. turn around) One of the final four entries is used when Willy is being pulled both left and right; each entry leaves the flags at 85D0 unchanged (so Willy carries on moving in the direction he's already moving, or remains stationary). 842D DEFB \$00 V=V'=0 (facing right, no movement) 842E DEFB \$01 V=V'=1 (facing left, no movement) 842F DEFB \$02 V=V'=2 (facing right, moving) 8430 DEFB \$03 V=V'=3 (facing left, moving)
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