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Improved control support for diagonal inputs

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The original Pac-Man machine uses a 4-way joystick, which makes it
impossible to generate more than one direction input. The game does
not understand diagonals, and will use the first direction found to
be pressed. This can cause frustration when played on the keyboard
or with a regular 8-way joystick.

We now ignore control input for the direction Pac-Man is currently
facing, so changes of direction are always preferred. We also ignore
perpendicular inputs on tile entry, to defeat the turn overshoot
mechanism that gives a brief window for players to change their mind
about a turn.

These changes are only active when diagonal inputs are detected, so
traditional play with a single input remains true to the original.
This commit is contained in:
Simon Owen
2014-03-01 16:41:53 +00:00
parent 9f75a8d527
commit c07623e135
1 changed files with 41 additions and 13 deletions
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54
pacemuzx.asm
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@ -44,6 +44,10 @@ pac_footer: equ &4000 ; credit and fruit display
pac_chars: equ &4040 ; start of main Pac-Man display (skipping the score rows)
pac_header: equ &43c0 ; 64 bytes containing the score
pac_ypos: equ &4d08 ; Pac-Man y position (as viewed)
pac_xpos: equ &4d09 ; Pac-Man x position (as viewed)
pac_dir: equ &4d30 ; Pac-Man facing direction (0=right, 1=down, 2=left, 3=up)
; address of saved sprite block followed by the data itself
spr_save_2: equ &5b00
spr_save_3: equ spr_save_2+2+2+(3*12) ; attr address, data address, 3 bytes * 12 lines
@ -733,7 +737,7 @@ inp_col_lp: rra
bit 3,a ; 7 = white?
jr z,got_colour
rra
jp c,input_done
jp c,joy_done
got_colour: ld a,c
ld (attr_colour),a ; set to be picked up by flash_maze
@ -890,25 +894,49 @@ not_fire:
cp c ; was it the only bit?
jr z,joy_done ; skip if so
ld a,(last_controls); last valid (single) controls
xor c ; check for differences
or %11110000 ; convert to mask
ld c,a
ld a,d ; current controls
or %00001111 ; release all directions
and c ; press the changed key
jr joy_multi ; apply change but don't save
ld a,(pac_dir) ; facing direction (r/d/l/u)
bit 1,a
rra
ld c,&07 ; position mask for tile offset
jr c,face_ud
face_lr: ld a,(pac_xpos) ; x position
jr z,face_r ; (from bit test above)
face_l: set 1,d ; release left
and c ; mask to tile offset
cp 5 ; entering junction?
jr c,joy_done ; if not we're done
ignore_ud: set 0,d ; release up
set 3,d ; release down
jr joy_done
face_r: set 2,d ; release right
and c
cp 4 ; entering junction?
jr c,ignore_ud ; if so, ignore up+down
jr joy_done
face_ud: ld a,(pac_ypos) ; y position
jr z,face_d ; (from bit test above)
face_u: set 0,d ; release up
and c
cp 4 ; entering junction?
jr nc,joy_done ; if not we're done
ignore_lr: set 1,d ; release left
set 2,d ; release right
jr joy_done
face_d: set 3,d ; release down
and c
cp 5 ; entering junction?
jr nc,ignore_lr ; if so, ignore left+right
joy_done: ld a,d
ld (last_controls),a; update last valid controls
input_done: ld a,d ; use original value
joy_multi: ld (&5000),a
ld a,e
ld (&5040),a
ret
last_controls: defb 0
; Check sprite visibility, returns carry if any visible, no-carry if all hidden
is_visible: ld a,&10 ; minimum x/y position to be visible