From f2cb49ad2bf86eb7688aecfb88b17b2058ff0aa7 Mon Sep 17 00:00:00 2001
From: Joren <jorensc@riseup.net>
Date: Mon, 23 Mar 2026 12:38:23 +0100
Subject: [PATCH] Fix ghost and Pac-Man movement interpolation teleport

---
 pacman-project/adt/draw.rkt | 23 ++++++++++-------------
 1 file changed, 10 insertions(+), 13 deletions(-)

diff --git a/pacman-project/adt/draw.rkt b/pacman-project/adt/draw.rkt
index 7e7f291..0ef0b5e 100644
--- a/pacman-project/adt/draw.rkt
+++ b/pacman-project/adt/draw.rkt
@@ -262,20 +262,18 @@
           (+ a (* t (- b a))))
 
         ;; draw-pacman! :: pacman, number -> /
-        ;; Draws Pac-Man with offset backward interpolation. Uses
-        ;; lerp(prev, current, 0.5 + t/2) so the visual starts at the
-        ;; midpoint (max 0.5 tile lag) and arrives at current by t=1.
-        ;; No jumps on direction changes unlike forward extrapolation.
+        ;; Draws Pac-Man with smooth backward interpolation. Uses
+        ;; lerp(prev, current, t) so the visual smoothly transitions
+        ;; from the previous tile strictly to the current tile by t=1.
         (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))
-                 (factor (+ 0.5 (* 0.5 t)))
-                 (render-row (lerp prev-row row factor))
-                 (render-col (lerp prev-col col factor))
+                 (t (max 0 (min progress 1)))
+                 (render-row (lerp prev-row row t))
+                 (render-col (lerp prev-col col t))
                  (direction (pacman 'direction)))
             ((pacman-sprite 'set-x!) (grid->pixel-x render-col))
             ((pacman-sprite 'set-y!) (grid->pixel-y render-row))
@@ -285,7 +283,7 @@
                   ((eq? direction 'down) ((pacman-sprite 'rotate!) rotation-down)))))
 
         ;; draw-ghosts! :: list -> /
-        ;; Updates all ghost sprite positions with offset backward interpolation.
+        ;; Updates all ghost sprite positions with smooth backward interpolation.
         (define (draw-ghosts! ghosts)
           (for-each
            (lambda (ghost ghost-draw)
@@ -294,10 +292,9 @@
                     (col (pos 'col))
                     (prev-row (ghost 'prev-row))
                     (prev-col (ghost 'prev-col))
-                    (t (min (/ (ghost 'movement-timer) ghost-speed-ms) 1))
-                    (factor (+ 0.5 (* 0.5 t)))
-                    (render-row (lerp prev-row row factor))
-                    (render-col (lerp prev-col col factor))
+                    (t (max 0 (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!) render-row render-col dir)))
            ghosts ghost-draw-states))