From 01c6d334f76dd8f0b325cbf28d852f900a89aec9 Mon Sep 17 00:00:00 2001
From: Rokas Puzonas <rokas.puz@gmail.com>
Date: Fri, 2 Oct 2026 01:41:58 +0300
Subject: [PATCH] add position interpolation

---
 src/app.zig           | 40 +++++++++++++++++++++++++++++-----------
 src/platform/root.zig |  3 +--
 2 files changed, 30 insertions(+), 13 deletions(-)

diff --git a/src/app.zig b/src/app.zig
index 513b6c9..885ef8e 100644
--- a/src/app.zig
+++ b/src/app.zig
@@ -450,6 +450,7 @@ fn loadLevel(
                             .x = @intCast(ox),
                             .y = @intCast(oy),
                         },
+                        .visual_pos = .initFromInt(usize, ox, oy),
                         .sprite = self.tilesheet.get(pos.x, pos.y)
                     });
                 }
@@ -506,6 +507,8 @@ pub fn frame(self: *App, plt: Platform.Frame) !void {
     canvas.push();
     defer canvas.pop(clear_color);
 
+    const dt = plt.deltaTime();
+
     if (input.undo) {
         if (self.undo_stack.pop()) |undo_frame| {
             for (undo_frame.entities()) |e_state| {
@@ -525,8 +528,12 @@ pub fn frame(self: *App, plt: Platform.Frame) !void {
     {
         var entity_iter = self.world.entities.iterator();
         while (entity_iter.next()) |entity_id| {
+            var interpolate_pos = false;
+
             const entity = self.world.entities.getAssumeExists(entity_id);
             if (entity.type == .player) {
+                interpolate_pos = true;
+
                 const prev_player_direction = entity.player_direction;
                 if (tick_context.moveEntity(entity_id, input.move_dir)) {
                     if (entity.player_direction != prev_player_direction) {
@@ -536,9 +543,30 @@ pub fn frame(self: *App, plt: Platform.Frame) !void {
                     self.footstep_sound = Audio.play(.{ .buffer = self.footstep_buffer, .bus = self.sfx_bus });
                 }
 
+            } else if (entity.type == .box_goal) {
+                goal_count += 1;
+
+                if (self.world.entities.get(self.world.findEntity(entity.pos, .surface))) |above_entity| {
+                    if (above_entity.type == .box) {
+                        box_at_goal_count += 1;
+                    }
+                }
+            } else if (entity.type == .box) {
+                interpolate_pos = true;
+            }
+
+            const target_visual_pos = Vec2.initFromInt(i32, entity.pos.x, entity.pos.y);
+            var visual_step = target_visual_pos.sub(entity.visual_pos);
+            if (interpolate_pos) {
+                const speed = 10;
+                visual_step = visual_step.multiplyScalar(dt * speed);
+            }
+            entity.visual_pos = entity.visual_pos.add(visual_step);
+
+            if (entity.type == .player) {
                 const frames = self.player_sprites.getDirection(entity.player_direction);
 
-                if (input.move_dir.x != 0 or input.move_dir.y != 0) {
+                if (target_visual_pos.sub(entity.visual_pos).length() > 0.1) {
                     self.animation_timer += plt.input.delta_time;
                     const animatin_time = std.time.ns_per_s / 5;
                     while (self.animation_timer >= animatin_time) {
@@ -551,17 +579,7 @@ pub fn frame(self: *App, plt: Platform.Frame) !void {
                 }
 
                 entity.sprite = frames[entity.player_frame_index];
-            } else if (entity.type == .box_goal) {
-                goal_count += 1;
-
-                if (self.world.entities.get(self.world.findEntity(entity.pos, .surface))) |above_entity| {
-                    if (above_entity.type == .box) {
-                        box_at_goal_count += 1;
-                    }
-                }
             }
-
-            entity.visual_pos = .initFromInt(i32, entity.pos.x, entity.pos.y);
         }
     }
 
diff --git a/src/platform/root.zig b/src/platform/root.zig
index ee6d4d4..f26eb7c 100644
--- a/src/platform/root.zig
+++ b/src/platform/root.zig
@@ -106,10 +106,9 @@ fn PlatformType(App: type) type {
             _ = self.frame_arena.reset(.free_all); // TODO: make arena reset mode configurable
 
             const now = Io.Timestamp.now(self.io, .awake);
-            self.last_frame_at = now;
-
             self.input.now = @intCast(self.started_at.durationTo(now).nanoseconds);
             self.input.delta_time = @intCast(self.last_frame_at.durationTo(now).nanoseconds);
+            self.last_frame_at = now;
 
             if (self.input.keyboard.pressed.contains(.F4)) {
                 self.show_imgui = !self.show_imgui;