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7113: Advance left-facing ship or helicopter
Moves a left-facing ship/helicopter 2 pixels left, checking for terrain collision.
Input
B Y position
C X position
D Object definition
ship_or_helicopter_left_advance 7113 PUSH BC Save BC, calculate terrain check position: C -= 16 pixels.
7114 LD A,C
7115 SUB $10
7117 LD C,A
7118 CALL calculate_pixel_address Get terrain byte at (C, B). Load result into A.
711B LD A,(HL)
711C POP BC Restore BC. If terrain != 0, reverse direction.
711D CP $00
711F CALL NZ,reverse_enemy_direction
7122 LD ($8B0A),BC Store position to previous_object_coordinates. Advance X position left by 2 pixels (DEC C twice).
7126 DEC C
7127 DEC C
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