From 0c9136eaae595789577f8a8979a28e4f2fd9b4ea Mon Sep 17 00:00:00 2001
From: Steve Biedermann <hardliner66@gmail.com>
Date: Sun, 18 Oct 2026 23:15:16 +0200
Subject: [PATCH] feat!: move characters freely instead of tile by tile

Characters have a continuous Position simulated on the server with a
square collision box, sliding along walls and corner assist into
openings. GridPos is derived from the position, so interactions,
building and reach stay tile-based. The exact position is saved.

BREAKING CHANGE: protocol version 4 replaces SetMoveDir with SetMovement
and replicates Position.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 CHANGELOG.md                           |   7 +-
 README.md                              |   6 +-
 crates/game_client/src/input.rs        |  52 +++---
 crates/game_client/src/render.rs       |  25 +--
 crates/game_core/src/components.rs     |  18 +-
 crates/game_core/src/grid.rs           |   5 +
 crates/game_core/src/lib.rs            |   2 +-
 crates/game_core/src/protocol.rs       |  15 +-
 crates/game_server/src/actions.rs      |   7 +-
 crates/game_server/src/lib.rs          |   7 +-
 crates/game_server/src/movement.rs     | 248 ++++++++++++++++++++++---
 crates/game_server/src/persistence.rs  |   8 +-
 crates/game_server/src/players.rs      |  11 +-
 crates/game_server/src/survival.rs     |   7 +-
 crates/game_server/tests/simulation.rs |  25 ++-
 15 files changed, 345 insertions(+), 98 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index fe01b44..19956fe 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -49,8 +49,11 @@ based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 
 ### Changed
 
-- **Breaking:** network protocol version 3. Logins carry a player id and
-  password, so older clients and servers can't connect. Characters saved by name
+- Characters move freely instead of tile by tile: diagonal movement, sliding
+  along walls and around corners. Their exact position is saved.
+- **Breaking:** network protocol version 4. Logins carry a player id and
+  password, and movement is sent as a direction vector, so older clients and
+  servers can't connect. Characters saved by name
   in existing worlds are not carried over to player ids.
 
 ### Removed
diff --git a/README.md b/README.md
index 5ad6a2a..78f2736 100644
--- a/README.md
+++ b/README.md
@@ -11,6 +11,8 @@ with [Bevy](https://bevy.org) in Rust.
 - **Tiled maps** – maps are regular [Tiled](https://www.mapeditor.org) `.tmx` files.
 - **Persistent world** – no rounds. The world and every character (inventory, skills,
   vitals, position) are saved and restored across restarts.
+- **Free movement** – characters walk anywhere, not tile by tile, and slide along
+  walls. Interactions still target the tile you face.
 - **Singleplayer and multiplayer** – one authoritative server simulation, used locally
   in singleplayer and over UDP in multiplayer
   ([bevy_replicon](https://crates.io/crates/bevy_replicon) + renet).
@@ -23,7 +25,7 @@ with [Bevy](https://bevy.org) in Rust.
 | `crates/game_server` | Authoritative simulation, Rune scripting, persistence, `game-server` binary |
 | `crates/game_client` | Rendering, UI and input (`game` binary); embeds the server for singleplayer/host |
 
-The client never changes game state directly. It sends requests (`Login`, `SetMoveDir`,
+The client never changes game state directly. It sends requests (`Login`, `SetMovement`,
 `Interact`, `Craft`, …) and the server replicates the resulting state back. In
 singleplayer the same server systems run inside the client process, so singleplayer and
 multiplayer behave identically.
@@ -144,7 +146,7 @@ in-game chat. Admin commands change `server.toml` (or `host.toml`) immediately.
 
 | Key                 | Action                                               |
 |---------------------|------------------------------------------------------|
-| WASD / arrows       | Move (you face the direction you move)               |
+| WASD / arrows       | Move freely, also diagonally (you face that way)     |
 | E                   | Pick up (own tile, otherwise the faced tile)         |
 | F / left click      | Interact with the faced / clicked building; machines open their window |
 | U                   | Use the selected item (eat, heal, …)                 |
diff --git a/crates/game_client/src/input.rs b/crates/game_client/src/input.rs
index a1ba0d7..73b54ff 100644
--- a/crates/game_client/src/input.rs
+++ b/crates/game_client/src/input.rs
@@ -72,44 +72,34 @@ fn window_keys(
     }
 }
 
-const MOVE_KEYS: [(KeyCode, Dir); 8] = [
-    (KeyCode::KeyW, Dir::North),
-    (KeyCode::ArrowUp, Dir::North),
-    (KeyCode::KeyS, Dir::South),
-    (KeyCode::ArrowDown, Dir::South),
-    (KeyCode::KeyA, Dir::West),
-    (KeyCode::ArrowLeft, Dir::West),
-    (KeyCode::KeyD, Dir::East),
-    (KeyCode::ArrowRight, Dir::East),
-];
-
-/// Sends the held direction whenever it changes. The most recently pressed key wins.
+/// Sends the held movement direction whenever it changes.
 fn movement(
     mut commands: Commands,
     keys: Res<ButtonInput<KeyCode>>,
     ui: Res<UiState>,
     focus: Res<UiFocus>,
-    mut held: Local<Vec<Dir>>,
-    mut sent: Local<Option<Dir>>,
+    mut sent: Local<SetMovement>,
 ) {
-    held.retain(|dir| {
-        MOVE_KEYS
-            .iter()
-            .any(|(key, d)| d == dir && keys.pressed(*key))
-    });
-    for (key, dir) in MOVE_KEYS {
-        if keys.just_pressed(key) && !held.contains(&dir) {
-            held.push(dir);
-        }
-    }
-    let dir = if ui.blocks_game() || ui.chat_open || focus.captures_keyboard() {
-        None
-    } else {
-        held.last().copied()
+    let axis = |neg: [KeyCode; 2], pos: [KeyCode; 2]| {
+        i8::from(keys.any_pressed(pos)) - i8::from(keys.any_pressed(neg))
     };
-    if *sent != dir {
-        *sent = dir;
-        commands.client_trigger(SetMoveDir(dir));
+    let movement = if ui.blocks_game() || ui.chat_open || focus.captures_keyboard() {
+        SetMovement::default()
+    } else {
+        SetMovement {
+            x: axis(
+                [KeyCode::KeyA, KeyCode::ArrowLeft],
+                [KeyCode::KeyD, KeyCode::ArrowRight],
+            ),
+            y: axis(
+                [KeyCode::KeyW, KeyCode::ArrowUp],
+                [KeyCode::KeyS, KeyCode::ArrowDown],
+            ),
+        }
+    };
+    if *sent != movement {
+        *sent = movement;
+        commands.client_trigger(movement);
     }
 }
 
diff --git a/crates/game_client/src/render.rs b/crates/game_client/src/render.rs
index ac4b8da..048e2d6 100644
--- a/crates/game_client/src/render.rs
+++ b/crates/game_client/src/render.rs
@@ -4,7 +4,7 @@ use bevy::prelude::*;
 use game_core::{
     GameData,
     components::*,
-    grid::{Dir, TILE_SIZE, grid_to_world},
+    grid::{Dir, TILE_SIZE, grid_to_world, position_to_world},
     map::MapLayout,
 };
 
@@ -223,7 +223,7 @@ fn character_visuals(
     mut commands: Commands,
     asset_server: Res<AssetServer>,
     local: Res<LocalCharacter>,
-    added: Query<(Entity, &Character, &GridPos), Added<Character>>,
+    added: Query<(Entity, &Character, &Position), Added<Character>>,
     mut facing: Query<(&Facing, &mut Sprite), (With<Character>, Changed<Facing>)>,
 ) {
     for (entity, character, pos) in &added {
@@ -233,7 +233,7 @@ fn character_visuals(
         }
         commands.entity(entity).insert((
             sprite,
-            Transform::from_translation(grid_to_world(*pos).extend(Z_CHARACTER)),
+            Transform::from_translation(position_to_world(pos.0).extend(Z_CHARACTER)),
             Visibility::default(),
             children![(
                 Text2d::new(character.name.clone()),
@@ -247,22 +247,23 @@ fn character_visuals(
     }
 }
 
-/// Glides characters between tiles; teleports for large jumps (respawn, login).
+/// Smooths replicated positions, which arrive at the server tick rate; teleports for large
+/// jumps (respawn, login).
 fn move_characters(
     time: Res<Time>,
-    mut characters: Query<(&GridPos, &mut Transform), With<Character>>,
+    mut characters: Query<(&Position, &mut Transform), With<Character>>,
 ) {
-    let speed = TILE_SIZE / game_server::movement::MOVE_DELAY * 1.2;
+    let t = 1.0 - (-20.0 * time.delta_secs()).exp();
     for (pos, mut transform) in &mut characters {
-        let target = grid_to_world(*pos);
+        let target = position_to_world(pos.0);
         let current = transform.translation.truncate();
         let delta = target - current;
-        if delta.length() > TILE_SIZE * 3.0 {
-            transform.translation = target.extend(Z_CHARACTER);
+        let next = if delta.length() > TILE_SIZE * 3.0 {
+            target
         } else {
-            let step = delta.clamp_length_max(speed * time.delta_secs());
-            transform.translation += step.extend(0.0);
-        }
+            current + delta * t
+        };
+        transform.translation = next.extend(Z_CHARACTER);
     }
 }
 
diff --git a/crates/game_core/src/components.rs b/crates/game_core/src/components.rs
index 1044be9..1501031 100644
--- a/crates/game_core/src/components.rs
+++ b/crates/game_core/src/components.rs
@@ -35,12 +35,28 @@ impl GridPos {
     }
 }
 
+/// Free position of a character in tiles, in Tiled's coordinate system (`y` down).
+/// Tile `(x, y)` covers `x..x + 1` and `y..y + 1`. The server keeps the character's
+/// [`GridPos`] at the tile containing this point.
+#[derive(Component, Clone, Copy, Debug, Default, PartialEq, Serialize, Deserialize)]
+pub struct Position(pub Vec2);
+
+impl Position {
+    pub fn center_of(tile: GridPos) -> Self {
+        Self(Vec2::new(tile.x as f32 + 0.5, tile.y as f32 + 0.5))
+    }
+
+    pub fn tile(self) -> GridPos {
+        GridPos::new(self.0.x.floor() as i32, self.0.y.floor() as i32)
+    }
+}
+
 #[derive(Component, Clone, Copy, Debug, Default, PartialEq, Eq, Serialize, Deserialize)]
 pub struct Facing(pub Dir);
 
 /// A player character. Names are unique and identify the persistent character.
 #[derive(Component, Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
-#[require(GridPos, Facing, Vitals, Inventory, Skills)]
+#[require(GridPos, Position, Facing, Vitals, Inventory, Skills)]
 pub struct Character {
     pub name: String,
 }
diff --git a/crates/game_core/src/grid.rs b/crates/game_core/src/grid.rs
index a1340b0..a3ddd26 100644
--- a/crates/game_core/src/grid.rs
+++ b/crates/game_core/src/grid.rs
@@ -28,6 +28,11 @@ impl Dir {
     }
 }
 
+/// Converts a [`Position`](crate::components::Position) in tiles to Bevy world space (y up).
+pub fn position_to_world(pos: Vec2) -> Vec2 {
+    Vec2::new(pos.x * TILE_SIZE, -pos.y * TILE_SIZE)
+}
+
 /// Converts a grid position to the center of the tile in Bevy world space (y up).
 pub fn grid_to_world(pos: GridPos) -> Vec2 {
     Vec2::new(
diff --git a/crates/game_core/src/lib.rs b/crates/game_core/src/lib.rs
index 735b148..507b1f6 100644
--- a/crates/game_core/src/lib.rs
+++ b/crates/game_core/src/lib.rs
@@ -16,7 +16,7 @@ pub use data::GameData;
 pub const DEFAULT_MAP: &str = "maps/station.tmx";
 pub const DEFAULT_PORT: u16 = 5000;
 /// Bump when the protocol changes in incompatible ways.
-pub const PROTOCOL_ID: u64 = 3;
+pub const PROTOCOL_ID: u64 = 4;
 
 /// Locates the `assets` directory.
 ///
diff --git a/crates/game_core/src/protocol.rs b/crates/game_core/src/protocol.rs
index 61d087f..b0c412b 100644
--- a/crates/game_core/src/protocol.rs
+++ b/crates/game_core/src/protocol.rs
@@ -7,7 +7,7 @@ use bevy::prelude::*;
 use bevy_replicon::prelude::*;
 use serde::{Deserialize, Serialize};
 
-use crate::{components::*, grid::Dir};
+use crate::components::*;
 
 /// First event a client sends; selects (or creates) the persistent character.
 #[derive(Event, Clone, Debug, Serialize, Deserialize)]
@@ -21,9 +21,13 @@ pub struct Login {
     pub password: String,
 }
 
-/// Direction the player is holding, `None` to stop.
-#[derive(Event, Clone, Debug, Serialize, Deserialize)]
-pub struct SetMoveDir(pub Option<Dir>);
+/// Movement keys the player is holding: `x` and `y` are -1, 0 or 1 (`y` down,
+/// both 0 to stop). Diagonals move at the same speed as straight lines.
+#[derive(Event, Clone, Copy, Debug, Default, PartialEq, Eq, Serialize, Deserialize)]
+pub struct SetMovement {
+    pub x: i8,
+    pub y: i8,
+}
 
 /// Pick up the item on the given tile (own or adjacent).
 #[derive(Event, Clone, Debug, Serialize, Deserialize)]
@@ -121,6 +125,7 @@ impl Plugin for ProtocolPlugin {
     fn build(&self, app: &mut App) {
         app.replicate::<WorldMap>()
             .replicate::<GridPos>()
+            .replicate::<Position>()
             .replicate::<Facing>()
             .replicate::<Character>()
             .replicate::<Vitals>()
@@ -131,7 +136,7 @@ impl Plugin for ProtocolPlugin {
             .replicate::<BuildingState>()
             .replicate::<Machine>()
             .add_client_event::<Login>(Channel::Ordered)
-            .add_client_event::<SetMoveDir>(Channel::Ordered)
+            .add_client_event::<SetMovement>(Channel::Ordered)
             .add_client_event::<PickUp>(Channel::Ordered)
             .add_client_event::<Interact>(Channel::Ordered)
             .add_client_event::<UseItem>(Channel::Ordered)
diff --git a/crates/game_server/src/actions.rs b/crates/game_server/src/actions.rs
index b473ba3..97c64fe 100644
--- a/crates/game_server/src/actions.rs
+++ b/crates/game_server/src/actions.rs
@@ -10,6 +10,7 @@ use game_core::{GameData, components::*, protocol::*};
 
 use crate::{
     crafting::{self, item_name},
+    movement,
     players::{Players, tell},
     scripting::{ScriptEngine, ScriptState, ScriptTarget},
     world::{WorldLayout, spawn_building, spawn_ground_item},
@@ -442,7 +443,7 @@ pub fn on_construct(
     layout: Res<WorldLayout>,
     mut characters: Characters,
     buildings: Query<&GridPos, (With<Building>, Without<Character>)>,
-    occupants: Query<&GridPos, (With<Character>, Without<Building>)>,
+    occupants: Query<&Position, (With<Character>, Without<Building>)>,
 ) {
     let client = ev.client_id;
     let target = ev.message.target;
@@ -450,7 +451,9 @@ pub fn on_construct(
         return;
     };
     // Checked before borrowing the actor mutably.
-    let occupied = occupants.iter().any(|p| *p == target);
+    let occupied = occupants
+        .iter()
+        .any(|p| movement::overlaps_tile(p.0, target));
     let Ok((_, pos, mut facing, mut inventory, _, mut skills)) = characters.get_mut(entity) else {
         return;
     };
diff --git a/crates/game_server/src/lib.rs b/crates/game_server/src/lib.rs
index 0ba20db..a943b24 100644
--- a/crates/game_server/src/lib.rs
+++ b/crates/game_server/src/lib.rs
@@ -78,10 +78,11 @@ impl Plugin for GameServerPlugin {
             .add_systems(
                 FixedUpdate,
                 (
-                    movement::move_characters,
-                    survival::tick_survival,
+                    (movement::move_characters, survival::tick_survival),
+                    movement::sync_tiles,
                     machines::tick_machines,
                 )
+                    .chain()
                     .run_if(resource_exists::<world::WorldLayout>),
             )
             .add_systems(
@@ -95,7 +96,7 @@ impl Plugin for GameServerPlugin {
             .add_observer(players::on_login)
             .add_observer(players::on_disconnect)
             .add_observer(players::on_chat)
-            .add_observer(movement::on_set_move_dir)
+            .add_observer(movement::on_set_movement)
             .add_observer(actions::on_pick_up)
             .add_observer(actions::on_drop_item)
             .add_observer(actions::on_use_item)
diff --git a/crates/game_server/src/movement.rs b/crates/game_server/src/movement.rs
index 2ff41ff..3c29f0a 100644
--- a/crates/game_server/src/movement.rs
+++ b/crates/game_server/src/movement.rs
@@ -1,58 +1,248 @@
-//! Tile-based character movement.
+//! Free character movement with collision against solid tiles and buildings.
+
+use std::collections::HashSet;
 
 use bevy::prelude::*;
 use bevy_replicon::prelude::*;
-use game_core::{components::*, grid::Dir, protocol::SetMoveDir};
+use game_core::{components::*, grid::Dir, protocol::SetMovement};
 
-use crate::{
-    players::Players,
-    world::{WorldLayout, is_blocked},
-};
+use crate::{players::Players, world::WorldLayout};
 
-/// Seconds per tile step.
-pub const MOVE_DELAY: f32 = 0.16;
+/// Walking speed in tiles per second.
+pub const MOVE_SPEED: f32 = 4.5;
+/// Half the side of a character's square collision box, in tiles. Less than 0.5,
+/// so characters fit through one tile wide gaps.
+pub const CHARACTER_RADIUS: f32 = 0.3;
+/// How far (in tiles) a character blocked by a corner is pushed sideways
+/// towards an opening, so doorways don't need pixel-exact aiming.
+const CORNER_ASSIST: f32 = 0.45;
+/// Gap left between a character and the obstacle it touches.
+const CONTACT_GAP: f32 = 1e-3;
+/// Longest movement per collision step, below the box size so no tile is skipped.
+const MAX_STEP: f32 = 0.25;
 
+/// Normalized walking direction (`y` down), zero when standing still.
 #[derive(Component, Default, Debug)]
-pub struct MoveIntent {
-    pub dir: Option<Dir>,
-    pub cooldown: f32,
-}
+pub struct MoveIntent(pub Vec2);
 
-pub fn on_set_move_dir(
-    ev: On<FromClient<SetMoveDir>>,
+pub fn on_set_movement(
+    ev: On<FromClient<SetMovement>>,
     players: Res<Players>,
     mut intents: Query<(&mut MoveIntent, &mut Facing)>,
 ) {
     let Some(&entity) = players.by_client.get(&ev.client_id) else {
         return;
     };
-    if let Ok((mut intent, mut facing)) = intents.get_mut(entity) {
-        intent.dir = ev.message.0;
-        if let Some(dir) = intent.dir {
-            facing.set_if_neq(Facing(dir));
-        }
+    let Ok((mut intent, mut facing)) = intents.get_mut(entity) else {
+        return;
+    };
+    let input = Vec2::new(ev.message.x.signum() as f32, ev.message.y.signum() as f32);
+    intent.0 = input.normalize_or_zero();
+    if let Some(dir) = facing_for(input, facing.0) {
+        facing.set_if_neq(Facing(dir));
     }
 }
 
+/// Facing for a movement input. While moving diagonally, the current facing is kept
+/// if it is one of the two directions, so it doesn't flip back and forth.
+fn facing_for(input: Vec2, current: Dir) -> Option<Dir> {
+    let horizontal = match input.x {
+        x if x > 0.0 => Some(Dir::East),
+        x if x < 0.0 => Some(Dir::West),
+        _ => None,
+    };
+    let vertical = match input.y {
+        y if y > 0.0 => Some(Dir::South),
+        y if y < 0.0 => Some(Dir::North),
+        _ => None,
+    };
+    if horizontal == Some(current) || vertical == Some(current) {
+        return Some(current);
+    }
+    horizontal.or(vertical)
+}
+
 pub fn move_characters(
     time: Res<Time>,
     layout: Option<Res<WorldLayout>>,
     buildings: Query<(&GridPos, &BuildingState), (With<Building>, Without<Character>)>,
-    mut characters: Query<(&mut MoveIntent, &mut GridPos, &mut Facing), With<Character>>,
+    mut characters: Query<(&MoveIntent, &mut Position), With<Character>>,
 ) {
     let Some(layout) = layout else { return };
+    let solid: HashSet<GridPos> = buildings
+        .iter()
+        .filter(|(_, state)| state.solid)
+        .map(|(pos, _)| *pos)
+        .collect();
+    let blocked = |tile: GridPos| layout.0.is_solid(tile) || solid.contains(&tile);
     let dt = time.delta_secs();
-    for (mut intent, mut pos, mut facing) in &mut characters {
-        intent.cooldown = (intent.cooldown - dt).max(0.0);
-        let Some(dir) = intent.dir else { continue };
-        if intent.cooldown > 0.0 {
+    for (intent, mut pos) in &mut characters {
+        if intent.0 == Vec2::ZERO {
             continue;
         }
-        facing.set_if_neq(Facing(dir));
-        let next = pos.step(dir);
-        if !is_blocked(next, &layout.0, buildings.iter()) {
-            *pos = next;
-            intent.cooldown = MOVE_DELAY;
+        let next = slide(pos.0, intent.0 * MOVE_SPEED * dt, &blocked);
+        if next != pos.0 {
+            pos.0 = next;
         }
     }
 }
+
+/// Keeps [`GridPos`] at the tile under each character, for tile-based interactions.
+pub fn sync_tiles(mut characters: Query<(&Position, &mut GridPos), Changed<Position>>) {
+    for (pos, mut tile) in &mut characters {
+        tile.set_if_neq(pos.tile());
+    }
+}
+
+/// Tiles overlapped by a character's collision box at `pos`.
+fn box_tiles(pos: Vec2) -> impl Iterator<Item = GridPos> {
+    let min = (pos - CHARACTER_RADIUS).floor().as_ivec2();
+    let max = (pos + CHARACTER_RADIUS).floor().as_ivec2();
+    (min.y..=max.y).flat_map(move |y| (min.x..=max.x).map(move |x| GridPos::new(x, y)))
+}
+
+/// Whether a character at `pos` overlaps `tile`.
+pub fn overlaps_tile(pos: Vec2, tile: GridPos) -> bool {
+    box_tiles(pos).any(|t| t == tile)
+}
+
+/// Whether moving from `from` to `to` makes the box overlap a blocked tile. Tiles it
+/// already overlaps don't count, so characters can walk out of a door that closed on them.
+fn enters_blocked(from: Vec2, to: Vec2, blocked: &impl Fn(GridPos) -> bool) -> bool {
+    let old: Vec<GridPos> = box_tiles(from).collect();
+    box_tiles(to).any(|tile| !old.contains(&tile) && blocked(tile))
+}
+
+/// Moves a character's box by `delta`, sliding along obstacles and around corners.
+pub fn slide(mut pos: Vec2, delta: Vec2, blocked: &impl Fn(GridPos) -> bool) -> Vec2 {
+    let steps = (delta.abs().max_element() / MAX_STEP).ceil().max(1.0);
+    let step = delta / steps;
+    for _ in 0..steps as u32 {
+        let mut progressed = [false; 2];
+        for axis in 0..2 {
+            if step[axis] == 0.0 {
+                continue;
+            }
+            let mut next = pos;
+            next[axis] += step[axis];
+            if enters_blocked(pos, next, blocked) {
+                // Move up to the obstacle instead.
+                next[axis] = if step[axis] > 0.0 {
+                    (next[axis] + CHARACTER_RADIUS).floor() - CHARACTER_RADIUS - CONTACT_GAP
+                } else {
+                    (next[axis] - CHARACTER_RADIUS).floor() + 1.0 + CHARACTER_RADIUS + CONTACT_GAP
+                };
+                if (next[axis] - pos[axis]) * step[axis] <= 0.0
+                    || enters_blocked(pos, next, blocked)
+                {
+                    continue;
+                }
+            }
+            progressed[axis] = next[axis] != pos[axis];
+            pos = next;
+        }
+        for axis in 0..2 {
+            let other = 1 - axis;
+            if !progressed[axis] && step[axis] != 0.0 && step[other] == 0.0 {
+                pos = assist(pos, axis, step[axis], blocked);
+            }
+        }
+    }
+    pos
+}
+
+/// Shifts a character blocked along `axis` sideways towards a nearby opening.
+fn assist(pos: Vec2, axis: usize, step: f32, blocked: &impl Fn(GridPos) -> bool) -> Vec2 {
+    let other = 1 - axis;
+    let row = pos[other].floor();
+    let mut lanes = [row - 0.5, row + 0.5, row + 1.5];
+    lanes.sort_by(|a, b| (a - pos[other]).abs().total_cmp(&(b - pos[other]).abs()));
+    for lane in lanes {
+        let offset = lane - pos[other];
+        if offset.abs() > CORNER_ASSIST {
+            continue;
+        }
+        // Centered in the lane, would the character get ahead?
+        let mut probe = pos;
+        probe[other] = lane;
+        let mut ahead = probe;
+        ahead[axis] += step.signum() * (CHARACTER_RADIUS + CONTACT_GAP * 2.0).min(0.5);
+        if box_tiles(ahead).any(blocked) {
+            continue;
+        }
+        let mut next = pos;
+        next[other] += offset.clamp(-step.abs(), step.abs());
+        if !enters_blocked(pos, next, blocked) {
+            return next;
+        }
+    }
+    pos
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// A wall column at x = 2 with a gap at y = 1.
+    fn wall(tile: GridPos) -> bool {
+        tile.x == 2 && tile.y != 1
+    }
+
+    fn walk(mut pos: Vec2, dir: Vec2, seconds: f32) -> Vec2 {
+        let dt = 1.0 / 64.0;
+        for _ in 0..(seconds / dt) as u32 {
+            pos = slide(pos, dir.normalize() * MOVE_SPEED * dt, &wall);
+        }
+        pos
+    }
+
+    #[test]
+    fn moves_freely_between_tiles() {
+        let pos = slide(Vec2::new(0.5, 5.5), Vec2::new(0.3, 0.2), &wall);
+        assert!((pos - Vec2::new(0.8, 5.7)).length() < 1e-5, "{pos}");
+    }
+
+    #[test]
+    fn stops_at_walls_and_slides_along_them() {
+        let pos = walk(Vec2::new(0.5, 5.5), Vec2::new(1.0, 0.0), 1.0);
+        assert!((pos.x - (2.0 - CHARACTER_RADIUS)).abs() < 0.01, "{pos}");
+        assert_eq!(pos.y, 5.5);
+        let pos = walk(Vec2::new(0.5, 5.5), Vec2::new(1.0, 1.0), 1.0);
+        assert!(
+            pos.x < 2.0 - CHARACTER_RADIUS + 0.01 && pos.y > 7.0,
+            "{pos}"
+        );
+    }
+
+    #[test]
+    fn corners_guide_into_openings() {
+        // Slightly below the gap's center: the corner pushes the character into it.
+        let pos = walk(Vec2::new(0.5, 1.8), Vec2::new(1.0, 0.0), 1.5);
+        assert!(pos.x > 3.0, "{pos}");
+        assert_eq!(box_tiles(pos).map(|t| t.y).max(), Some(1), "{pos}");
+        assert_eq!(box_tiles(pos).map(|t| t.y).min(), Some(1), "{pos}");
+        // Far from the gap the wall just stops the character.
+        let pos = walk(Vec2::new(0.5, 3.5), Vec2::new(1.0, 0.0), 1.5);
+        assert!(pos.x < 2.0 && pos.y == 3.5, "{pos}");
+    }
+
+    #[test]
+    fn can_leave_blocked_tiles() {
+        let pos = walk(Vec2::new(2.5, 3.5), Vec2::new(-1.0, 0.0), 0.5);
+        assert!(pos.x < 2.0, "{pos}");
+    }
+
+    #[test]
+    fn facing_keeps_diagonal_component() {
+        assert_eq!(
+            facing_for(Vec2::new(1.0, 1.0), Dir::South),
+            Some(Dir::South)
+        );
+        assert_eq!(facing_for(Vec2::new(1.0, 1.0), Dir::North), Some(Dir::East));
+        assert_eq!(
+            facing_for(Vec2::new(0.0, -1.0), Dir::East),
+            Some(Dir::North)
+        );
+        assert_eq!(facing_for(Vec2::ZERO, Dir::East), None);
+    }
+}
diff --git a/crates/game_server/src/persistence.rs b/crates/game_server/src/persistence.rs
index 0f54edc..7f3fd87 100644
--- a/crates/game_server/src/persistence.rs
+++ b/crates/game_server/src/persistence.rs
@@ -87,6 +87,9 @@ pub enum StorageError {
 pub struct SavedCharacter {
     pub name: String,
     pub pos: GridPos,
+    /// Exact position within `pos`; missing in older saves.
+    #[serde(default)]
+    pub position: Option<Position>,
     pub facing: Dir,
     pub vitals: Vitals,
     pub inventory: Inventory,
@@ -629,17 +632,19 @@ pub fn snapshot(world: &mut World) -> SaveGame {
         &Character,
         &PlayerId,
         &GridPos,
+        &Position,
         &Facing,
         &Vitals,
         &Inventory,
         &Skills,
     )>();
-    for (c, id, pos, facing, vitals, inventory, skills) in q.iter(world) {
+    for (c, id, pos, position, facing, vitals, inventory, skills) in q.iter(world) {
         characters.insert(
             id.0.clone(),
             SavedCharacter {
                 name: c.name.clone(),
                 pos: *pos,
+                position: Some(*position),
                 facing: facing.0,
                 vitals: vitals.clone(),
                 inventory: inventory.clone(),
@@ -730,6 +735,7 @@ mod tests {
             SavedCharacter {
                 name: "Alice".into(),
                 pos: GridPos::new(3, -4),
+                position: Some(Position(Vec2::new(3.25, -3.5))),
                 facing: Dir::West,
                 vitals: Vitals {
                     health: 42.5,
diff --git a/crates/game_server/src/players.rs b/crates/game_server/src/players.rs
index e67d977..4f20a1e 100644
--- a/crates/game_server/src/players.rs
+++ b/crates/game_server/src/players.rs
@@ -256,6 +256,11 @@ fn handle_login(world: &mut World, client: ClientId, login: Login) {
         &world.resource::<WorldLayout>().0,
         &buildings.query(world),
     );
+    // The saved spot is only kept if the tile is still free.
+    let position = saved
+        .position
+        .filter(|p| p.tile() == pos)
+        .unwrap_or(Position::center_of(pos));
     let config = world.resource::<ServerConfig>().clone();
     let owner_id = world.resource::<ServerSettings>().owner.clone();
     let admin = is_admin(owner_id.as_deref(), &config, client, &player_id);
@@ -263,6 +268,7 @@ fn handle_login(world: &mut World, client: ClientId, login: Login) {
         Replicated,
         Character { name: name.clone() },
         pos,
+        position,
         Facing(saved.facing),
         saved.vitals,
         saved.inventory,
@@ -424,6 +430,7 @@ pub fn new_character_data(data: &GameData, name: &str, spawn: GridPos) -> SavedC
     SavedCharacter {
         name: name.to_owned(),
         pos: spawn,
+        position: None,
         facing: Default::default(),
         vitals: Vitals::default(),
         inventory,
@@ -441,6 +448,7 @@ pub fn on_disconnect(
         &Character,
         &PlayerId,
         &GridPos,
+        &Position,
         &Facing,
         &Vitals,
         &Inventory,
@@ -450,13 +458,14 @@ pub fn on_disconnect(
     let Some(entity) = players.by_client.remove(&ClientId::Client(remove.entity)) else {
         return;
     };
-    if let Ok((c, id, pos, facing, vitals, inventory, skills)) = characters.get(entity) {
+    if let Ok((c, id, pos, position, facing, vitals, inventory, skills)) = characters.get(entity) {
         info!("{} logged out", c.name);
         store.0.insert(
             id.0.clone(),
             SavedCharacter {
                 name: c.name.clone(),
                 pos: *pos,
+                position: Some(*position),
                 facing: facing.0,
                 vitals: vitals.clone(),
                 inventory: inventory.clone(),
diff --git a/crates/game_server/src/survival.rs b/crates/game_server/src/survival.rs
index b0d0fcd..00d1c14 100644
--- a/crates/game_server/src/survival.rs
+++ b/crates/game_server/src/survival.rs
@@ -30,7 +30,8 @@ pub fn tick_survival(
     mut characters: Query<(
         &Character,
         &Controller,
-        &mut GridPos,
+        &GridPos,
+        &mut Position,
         &mut Vitals,
         &mut Inventory,
     )>,
@@ -39,7 +40,7 @@ pub fn tick_survival(
         return;
     }
     let dt = timer.0.duration().as_secs_f32();
-    for (character, controller, mut pos, mut vitals, mut inventory) in &mut characters {
+    for (character, controller, pos, mut position, mut vitals, mut inventory) in &mut characters {
         vitals.nutrition = (vitals.nutrition - HUNGER_RATE * dt).max(0.0);
         if vitals.nutrition <= 0.0 {
             vitals.heal(-STARVATION_DAMAGE * dt);
@@ -56,7 +57,7 @@ pub fn tick_survival(
             spawn_ground_item(&mut commands, stack, *pos);
         }
         if let Some(spawn) = &spawn {
-            *pos = spawn.0;
+            *position = Position::center_of(spawn.0);
         }
         *vitals = Vitals {
             nutrition: 50.0,
diff --git a/crates/game_server/tests/simulation.rs b/crates/game_server/tests/simulation.rs
index bb43680..be36151 100644
--- a/crates/game_server/tests/simulation.rs
+++ b/crates/game_server/tests/simulation.rs
@@ -5,7 +5,7 @@ use std::time::Duration;
 
 use bevy::{prelude::*, state::app::StatesPlugin, time::TimeUpdateStrategy};
 use bevy_replicon::prelude::*;
-use game_core::{CorePlugin, components::*, grid::Dir, protocol::*};
+use game_core::{CorePlugin, components::*, protocol::*};
 use game_server::{GameServerPlugin, ServerSettings};
 
 #[derive(Resource, Default)]
@@ -108,14 +108,29 @@ fn login_move_and_interact() {
     let log = take_log(&mut app);
     assert!(log.iter().any(|t| t == "<Tester> hello there"), "{log:?}");
 
-    // Walk east one tile.
-    send(&mut app, SetMoveDir(Some(Dir::East)));
-    send(&mut app, SetMoveDir(None));
-    for _ in 0..5 {
+    // Walk east until the character crosses into the next tile.
+    let start_x = app.world().get::<Position>(me).unwrap().0.x;
+    send(&mut app, SetMovement { x: 1, y: 0 });
+    for _ in 0..20 {
+        if app.world().get::<GridPos>(me).unwrap().x != start.x {
+            break;
+        }
         app.update();
     }
+    send(&mut app, SetMovement::default());
     let pos = *app.world().get::<GridPos>(me).unwrap();
+    let position = *app.world().get::<Position>(me).unwrap();
     assert_eq!(pos, GridPos::new(start.x + 1, start.y), "start {start:?}");
+    assert_eq!(position.tile(), pos);
+    assert!(position.0.x > start_x + 0.5, "{position:?}");
+    for _ in 0..3 {
+        app.update();
+    }
+    assert_eq!(
+        app.world().get::<Position>(me).unwrap(),
+        &position,
+        "stopped"
+    );
 
     // Eat an apple through the Rune script.
     app.world_mut().get_mut::<Vitals>(me).unwrap().nutrition = 50.0;