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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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30
pacman-project/adt/level.rkt
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@@ -263,9 +263,11 @@
;; Handle tunnel teleportation
(cond
((< next-col 0)
((pos 'col!) (- (maze 'cols) 1)))
((pos 'col!) (- (maze 'cols) 1))
((ghost 'sync-prev!)))
((>= next-col (maze 'cols))
((pos 'col!) 0))
((pos 'col!) 0)
((ghost 'sync-prev!)))
(else
((ghost 'move!) (car delta) (cdr delta))))))
@@ -289,6 +291,7 @@
((pos 'row!) ghost-house-exit-row)
((pos 'col!) ghost-house-exit-col)
((ghost 'direction!) 'left)
((ghost 'sync-prev!))
(on-ghosts-changed!)))
;;
@@ -348,12 +351,12 @@
(when (and was-in-house? (not (ghost 'in-house?)))
(exit-ghost-house! ghost)
((ghost 'mode!) global-mode)))
;; Movement tick for active ghosts
;; Movement tick for active ghosts (carry residual time)
(when (not (ghost 'in-house?))
(let ((mt ((ghost 'advance-movement-timer!) delta-time)))
(when (>= mt ghost-speed-ms)
(advance-ghost! ghost)
((ghost 'reset-movement-timer!))))))
((ghost 'set-movement-timer!) (- mt ghost-speed-ms))))))
ghosts))
;;
@@ -389,7 +392,9 @@
((pac-pos 'row!) row))
((>= col (maze 'cols))
((pac-pos 'col!) 0)
((pac-pos 'row!) row)))))
((pac-pos 'row!) row)))
;; Prevent interpolation across the entire map
((pacman 'sync-prev!))))
;;
;; Movement logic
@@ -427,13 +432,19 @@
;; advance-pacman! :: -> /
(define (advance-pacman!)
(when (not (or ((timer 'time-up?)) game-over?))
(let ((current-dir (pacman 'direction)))
(let* ((current-dir (pacman 'direction))
(pos-before-row ((pacman 'position) 'row))
(pos-before-col ((pacman 'position) 'col)))
(cond
((and queued-direction (can-move? queued-direction))
(move-pacman! queued-direction)
(set! queued-direction #f))
((can-move? current-dir)
(move-pacman! current-dir))))))
(move-pacman! current-dir)))
;; If pacman didn't actually move, sync prev to avoid drift
(when (and (= ((pacman 'position) 'row) pos-before-row)
(= ((pacman 'position) 'col) pos-before-col))
((pacman 'sync-prev!))))))
;;
;; Pause logic
@@ -465,11 +476,11 @@
(define (update! delta-time)
(when (not (or paused? game-over?))
((timer 'decrease!) delta-time)
;; Pac-Man movement
;; Pac-Man movement (carry residual for smoother interpolation)
(set! movement-timer (+ movement-timer delta-time))
(when (>= movement-timer pacman-speed-ms)
(advance-pacman!)
(set! movement-timer 0)
(set! movement-timer (- movement-timer pacman-speed-ms))
(check-ghost-collision!))
;; Ghost mode cycling and movement
(update-ghost-mode! delta-time)
@@ -502,6 +513,7 @@
((eq? msg 'timer) timer)
((eq? msg 'paused?) paused?)
((eq? msg 'game-over?) game-over?)
((eq? msg 'pacman-movement-timer) movement-timer)
((eq? msg 'key-press!) key-press!)
((eq? msg 'update!) update!)
((eq? msg 'set-on-coins-changed!) set-on-coins-changed!)