Routines
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73f1: Apply gravity to Jetman if no thrust button detected.
Used by the routine at 74fa.
Input
IX Jetman object.
H New X position.
L New Thrust value.
73f1 ld a,l
73f2 ld ($5dc7),a
73f5 ld (ix+$01),h Set new Jetman X position
Check if thruster is being aplpied
73f8 ld a,($5cf3) Game options
73fb bit 1,a Use Joystick? Jump if so.
73fd jp nz,$743e
Induce a slight pause before reading keys - this is required so that the gravity kicks in. It also acts as an undocumented hover key.
7400 ld b,$02 Loop count: read left and right row of keys
7402 ld a,$ef Read top-right row of keys
7404 out ($fd),a Set port for reading keyboard
7406 in a,($fe) ...and read that row of keys
7408 and $1f
740a cp $1f Check if any keys on the row are pressed
740c jr nz,$7438 Jump if so - hover Jetman
740e ld a,$f7 Read top-left row of keys
7410 djnz $7404 ...and repeat
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