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Add smooth sub-tile interpolation for Pac-Man and ghosts

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Entities now move smoothly between tiles instead of snapping. Previous
positions are tracked in pacman and ghost ADTs; the draw layer linearly
interpolates between prev and current based on movement timer progress.

Residual time is carried across movement ticks for consistent speed at
varying frame rates. Teleportation and ghost house exits call sync-prev!
to prevent cross-map interpolation artifacts.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
This commit is contained in:
joren
2026-03-23 11:52:00 +01:00
parent 9028dd031c
commit f251478dd6
4 changed files with 88 additions and 22 deletions
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22
pacman-project/adt/ghost.rkt
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@@ -27,7 +27,9 @@
(scatter-target (make-position scatter-row scatter-col))
(house-timer exit-delay)
(movement-timer 0)
(reverse-queued? #f))
(reverse-queued? #f)
(prev-row start-row)
(prev-col start-col))
;; direction! :: symbol -> /
(define (direction! new-dir)
@@ -44,10 +46,20 @@
(set! mode new-mode))
;; move! :: number, number -> /
;; Saves previous position, then moves by delta.
(define (move! delta-row delta-col)
(set! prev-row (position 'row))
(set! prev-col (position 'col))
((position 'row!) (+ (position 'row) delta-row))
((position 'col!) (+ (position 'col) delta-col)))
;; sync-prev! :: -> /
;; Sets previous position to current. Call after teleportation
;; or ghost house exit to prevent long-range interpolation.
(define (sync-prev!)
(set! prev-row (position 'row))
(set! prev-col (position 'col)))
;; consume-reverse! :: -> boolean
;; Returns #t and clears the flag if a reverse was queued.
(define (consume-reverse!)
@@ -67,6 +79,10 @@
(define (reset-movement-timer!)
(set! movement-timer 0))
;; set-movement-timer! :: number -> /
(define (set-movement-timer! val)
(set! movement-timer val))
;; advance-movement-timer! :: number -> number
;; Returns updated movement timer value.
(define (advance-movement-timer! delta-time)
@@ -82,6 +98,9 @@
((eq? msg 'mode) mode)
((eq? msg 'mode!) mode!)
((eq? msg 'move!) move!)
((eq? msg 'prev-row) prev-row)
((eq? msg 'prev-col) prev-col)
((eq? msg 'sync-prev!) sync-prev!)
((eq? msg 'scatter-target) scatter-target)
((eq? msg 'in-house?) (eq? mode 'in-house))
((eq? msg 'consume-reverse!) consume-reverse!)
@@ -89,6 +108,7 @@
((eq? msg 'movement-timer) movement-timer)
((eq? msg 'advance-movement-timer!) advance-movement-timer!)
((eq? msg 'reset-movement-timer!) reset-movement-timer!)
((eq? msg 'set-movement-timer!) set-movement-timer!)
(else (error "Ghost ADT -- Unknown message:" msg))))
dispatch-ghost))))