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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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35
pacman-project/adt/draw.rkt
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@@ -256,27 +256,45 @@
(for-each (lambda (gds) ((gds 'animate!))) ghost-draw-states)
(set! time-since-last-animation 0)))
;; draw-pacman! :: pacman -> /
(define (draw-pacman! pacman)
;; lerp :: number, number, number -> number
;; Linear interpolation between a and b by factor t (0..1).
(define (lerp a b t)
(+ a (* t (- b a))))
;; draw-pacman! :: pacman, number -> /
;; Draws Pac-Man with smooth interpolation between tiles.
(define (draw-pacman! pacman progress)
(let* ((pos (pacman 'position))
(row (pos 'row))
(col (pos 'col))
(prev-row (pacman 'prev-row))
(prev-col (pacman 'prev-col))
(t (min progress 1))
(render-col (lerp prev-col col t))
(render-row (lerp prev-row row t))
(direction (pacman 'direction)))
((pacman-sprite 'set-x!) (grid->pixel-x (pos 'col)))
((pacman-sprite 'set-y!) (grid->pixel-y (pos 'row)))
((pacman-sprite 'set-x!) (grid->pixel-x render-col))
((pacman-sprite 'set-y!) (grid->pixel-y render-row))
(cond ((eq? direction 'right) ((pacman-sprite 'rotate!) rotation-right))
((eq? direction 'left) ((pacman-sprite 'rotate!) rotation-left))
((eq? direction 'up) ((pacman-sprite 'rotate!) rotation-up))
((eq? direction 'down) ((pacman-sprite 'rotate!) rotation-down)))))
;; draw-ghosts! :: list -> /
;; Updates all ghost sprite positions and directions.
;; Updates all ghost sprite positions with smooth interpolation.
(define (draw-ghosts! ghosts)
(for-each
(lambda (ghost ghost-draw)
(let* ((pos (ghost 'position))
(row (pos 'row))
(col (pos 'col))
(prev-row (ghost 'prev-row))
(prev-col (ghost 'prev-col))
(t (min (/ (ghost 'movement-timer) ghost-speed-ms) 1))
(render-row (lerp prev-row row t))
(render-col (lerp prev-col col t))
(dir (ghost 'direction)))
((ghost-draw 'update!) row col dir)))
((ghost-draw 'update!) render-row render-col dir)))
ghosts ghost-draw-states))
;; draw-ui! :: score, timer -> /
@@ -343,9 +361,10 @@
;; draw-game! :: game -> /
(define (draw-game! game)
(let* ((level (game 'level))
(timer (level 'timer)))
(timer (level 'timer))
(pac-progress (/ (level 'pacman-movement-timer) pacman-speed-ms)))
;; Always update (lightweight sprite property sets)
(draw-pacman! (level 'pacman))
(draw-pacman! (level 'pacman) pac-progress)
(draw-ghosts! (level 'ghosts))
;; Only redraw when dirty / changed
(draw-key! (level 'key))