Smooth lerping

client/src/game.rs

@@ -1,7 +1,7 @@
 mod pathfind;
 mod pixelhelper;
 
-use std::collections::VecDeque;
+use std::collections::{HashMap, VecDeque};
 
 use crate::assets::Image;
 use crate::input::{GameAction, InputState};
@@ -44,6 +44,23 @@ const ROUTE_COLOR: u8 = 0b000_000_10;
 /// Viewport geometry: 30×30 tiles of 8 px, top-left of the framebuffer.
 const VIEW_TILES: i32 = 30;
 const TILE_PX: i32 = 8;
+const VIEW_PX: i32 = VIEW_TILES * TILE_PX;
+
+/// Camera pan speed. The player walks 8 px per 167 ms ≈ 48 px/s; the camera is a bit
+/// faster, so it trails during movement and settles right after the player stops.
+const CAM_SPEED: f32 = 64.0; // px/s
+
+/// A position correction farther than this is a teleport — snap instead of panning.
+const CAM_SNAP_PX: f32 = 96.0;
+
+/// Render-side smoothing state for one entity: the previously confirmed tile and how
+/// long ago the current one was confirmed. Positions are tiles; rendering lerps between
+/// them in pixels over one movement interval.
+struct EntityLerp {
+    prev: (i32, i32),
+    cur:  (i32, i32),
+    t_ms: usize,
+}
 
 pub struct Game {
     #[allow(dead_code)]
@@ -59,9 +76,15 @@ pub struct Game {
     /// Planned route from click-to-move: tiles not yet sent to the server. Fed into
     /// `path` one step per `MOVE_INTERVAL_MS`. Keyboard input cancels it.
     route:            VecDeque<(i32, i32)>,
+    /// Viewport top-left in world pixels. Follows the player linearly instead of
+    /// snapping tile-to-tile; only rendering rounds it to whole pixels.
+    cam:              (f32, f32),
     move_accum_ms:    usize,
     idle_ms:          usize,
     entities:         Vec<EntityInfo>,
+    /// Per-entity interpolation state, keyed by entity id. Purely cosmetic — all game
+    /// logic keeps using the authoritative tile positions.
+    lerp:             HashMap<u32, EntityLerp>,
 }
 
 impl Game {
@@ -71,17 +94,23 @@ impl Game {
         let entity_tileset = Image::from_tga("assets/tilesets/entities.tga").to_tileset();
 
         let server_addr = "127.0.0.1:7777".parse().unwrap();
+        let player_pos = (16, 16);
         Game {
             tileset,
             entity_tileset,
             net:              NetClient::new(server_addr),
             player_entity_id: 0,
-            player_pos:       (16, 16),
+            player_pos,
             path:             VecDeque::new(),
             route:            VecDeque::new(),
+            cam:              (
+                (player_pos.0 * TILE_PX - VIEW_PX / 2) as f32,
+                (player_pos.1 * TILE_PX - VIEW_PX / 2) as f32,
+            ),
             move_accum_ms:    MOVE_INTERVAL_MS, // ready, so the first held step fires instantly
             idle_ms:          0,
             entities:         Vec::new(),
+            lerp:             HashMap::new(),
         }
     }
 
@@ -126,6 +155,7 @@ impl Game {
                         .map(|e| (e.pos_x as i32, e.pos_y as i32))
                         .unwrap_or(self.player_pos);
                     self.reconcile_path();
+                    self.track_lerp(&entities);
                     self.entities = entities;
                 }
                 NetEvent::Disconnected                 => println!("disconnected from server"),
@@ -137,6 +167,8 @@ impl Game {
             return Some(GameSignal::Quit);
         }
 
+        self.step_camera(dt);
+        self.step_lerp(dt);
         self.render_viewport(render_frame);
         None
     }
@@ -147,16 +179,43 @@ impl Game {
         self.path.back().copied().unwrap_or(self.player_pos)
     }
 
+    /// Where the camera wants to be: the viewport centered on the player's tile.
+    fn cam_target(&self) -> (f32, f32) {
+        (
+            (self.player_pos.0 * TILE_PX - VIEW_PX / 2) as f32,
+            (self.player_pos.1 * TILE_PX - VIEW_PX / 2) as f32,
+        )
+    }
+
+    /// The camera rounded to the pixel grid — the actual top-left of the rendered view.
+    fn cam_px(&self) -> (i32, i32) {
+        (self.cam.0.round() as i32, self.cam.1.round() as i32)
+    }
+
+    /// Follow the player linearly at `CAM_SPEED`, axis by axis. Corrections beyond
+    /// `CAM_SNAP_PX` (teleports, respawns) snap outright instead of panning across.
+    fn step_camera(&mut self, dt: usize) {
+        let (tx, ty) = self.cam_target();
+        if (tx - self.cam.0).abs().max((ty - self.cam.1).abs()) > CAM_SNAP_PX {
+            self.cam = (tx, ty);
+            return;
+        }
+        let step = CAM_SPEED * dt as f32 / 1000.0;
+        let approach = |c: f32, t: f32| {
+            if (t - c).abs() <= step { t } else { c + step * (t - c).signum() }
+        };
+        self.cam = (approach(self.cam.0, tx), approach(self.cam.1, ty));
+    }
+
     /// Click-to-move: translate a framebuffer click into a world tile and plan a route
     /// there. The route is only a client-side plan — it is executed as ordinary cardinal
     /// actions in `step_movement`, so the server keeps full authority over every step.
     fn handle_click(&mut self, (mx, my): (i32, i32)) {
-        if mx < 0 || my < 0 || mx >= VIEW_TILES * TILE_PX || my >= VIEW_TILES * TILE_PX {
+        if mx < 0 || my < 0 || mx >= VIEW_PX || my >= VIEW_PX {
             return; // outside the world viewport
         }
-        let ox = self.player_pos.0 - 15;
-        let oy = self.player_pos.1 - 15;
-        let goal = (ox + mx / TILE_PX, oy + my / TILE_PX);
+        let (cx, cy) = self.cam_px();
+        let goal = ((cx + mx).div_euclid(TILE_PX), (cy + my).div_euclid(TILE_PX));
 
         let found = pathfind::find_path(self.predicted_pos(), goal, |x, y| self.tile_blocked(x, y));
         match found {
@@ -216,6 +275,47 @@ impl Game {
         }
     }
 
+    /// Fold a fresh authoritative entity list into the interpolation table: a changed
+    /// position starts a new lerp from the old one, a jump of more than one tile
+    /// (Chebyshev — a teleport) snaps, and vanished entities are dropped.
+    fn track_lerp(&mut self, entities: &[EntityInfo]) {
+        for e in entities {
+            let cur = (e.pos_x as i32, e.pos_y as i32);
+            self.lerp.entry(e.id)
+                .and_modify(|l| {
+                    if l.cur != cur {
+                        let far = (cur.0 - l.cur.0).abs().max((cur.1 - l.cur.1).abs()) > 1;
+                        l.prev = if far { cur } else { l.cur };
+                        l.cur = cur;
+                        l.t_ms = 0;
+                    }
+                })
+                .or_insert(EntityLerp { prev: cur, cur, t_ms: 0 });
+        }
+        self.lerp.retain(|id, _| entities.iter().any(|e| e.id == *id));
+    }
+
+    /// Advance all interpolation clocks; each lerp completes after one movement interval.
+    fn step_lerp(&mut self, dt: usize) {
+        for l in self.lerp.values_mut() {
+            l.t_ms = (l.t_ms + dt).min(MOVE_INTERVAL_MS);
+        }
+    }
+
+    /// An entity's render position in world pixels: between its previous and current
+    /// tile, proportional to the time since the current one was confirmed.
+    fn entity_px(&self, e: &EntityInfo) -> (i32, i32) {
+        let cur = (e.pos_x as i32 * TILE_PX, e.pos_y as i32 * TILE_PX);
+        match self.lerp.get(&e.id) {
+            Some(l) => {
+                let f = l.t_ms as f32 / MOVE_INTERVAL_MS as f32;
+                let mix = |a: i32, b: i32| a + ((b - a) as f32 * f).round() as i32;
+                (mix(l.prev.0 * TILE_PX, cur.0), mix(l.prev.1 * TILE_PX, cur.1))
+            }
+            None => cur,
+        }
+    }
+
     /// Reconcile the queued path against a fresh authoritative position: drop every queued
     /// tile up to and including the one the server has now reached.
     fn reconcile_path(&mut self) {
@@ -230,20 +330,25 @@ impl Game {
 
         frame.fill(0);
 
-        let ox = self.player_pos.0 - 15;
-        let oy = self.player_pos.1 - 15;
+        let (cx, cy) = self.cam_px();
+        let tx0 = cx.div_euclid(TILE_PX);
+        let ty0 = cy.div_euclid(TILE_PX);
+        let sx = -cx.rem_euclid(TILE_PX);
+        let sy = -cy.rem_euclid(TILE_PX);
 
-        for vy in 0..30i32 {
-            for vx in 0..30i32 {
-                let wx = ox + vx;
-                let wy = oy + vy;
+        // One extra row and column: with a sub-tile camera offset the viewport spans
+        // partial tiles on both edges.
+        for vy in 0..=VIEW_TILES {
+            for vx in 0..=VIEW_TILES {
+                let wx = tx0 + vx;
+                let wy = ty0 + vy;
                 let cid = chunk_id(wx.div_euclid(32) as i16, wy.div_euclid(32) as i16);
                 let tile_idx = wy.rem_euclid(32) as usize * 32 + wx.rem_euclid(32) as usize;
                 let tile_id = self.net.chunk_cache.get(&cid)
                     .map(|c| c.tiles[tile_idx])
                     .unwrap_or(0);
-                let px = vx * 8;
-                let py = vy * 8;
+                let px = sx + vx * TILE_PX;
+                let py = sy + vy * TILE_PX;
                 if let Some(tile) = self.tileset.get(tile_id as usize) {
                     pixelhelper::blit_tile(frame, W, px, py, tile);
                 } else {
@@ -261,11 +366,9 @@ impl Game {
         let marks = self.path.iter().map(|&p| (p, PATH_COLOR))
             .chain(self.route.iter().map(|&p| (p, ROUTE_COLOR)));
         for ((wx, wy), color) in marks {
-            let vx = wx - ox;
-            let vy = wy - oy;
-            if vx < 0 || vx >= 30 || vy < 0 || vy >= 30 { continue; }
-            let px = vx * 8;
-            let py = vy * 8;
+            let px = wx * TILE_PX - cx;
+            let py = wy * TILE_PX - cy;
+            if px <= -TILE_PX || px >= VIEW_PX || py <= -TILE_PX || py >= VIEW_PX { continue; }
             for dy in 0..8 {
                 for dx in 0..8 {
                     pixelhelper::set_pixel(frame, W, px + dx, py + dy, color);
@@ -273,14 +376,22 @@ impl Game {
             }
         }
 
-        // Entity pass — every entity at its authoritative server position.
+        // Entity pass — interpolated between the last two confirmed positions.
         for e in &self.entities {
-            let vx = e.pos_x as i32 - ox;
-            let vy = e.pos_y as i32 - oy;
-            if vx < 0 || vx >= 30 || vy < 0 || vy >= 30 { continue; }
+            let (ex, ey) = self.entity_px(e);
+            let px = ex - cx;
+            let py = ey - cy;
+            if px <= -TILE_PX || px >= VIEW_PX || py <= -TILE_PX || py >= VIEW_PX { continue; }
             if let Some(tile) = self.entity_tileset.get(e.type_id as usize) {
-                pixelhelper::blit_tile(frame, W, vx * 8, vy * 8, tile);
+                pixelhelper::blit_tile(frame, W, px, py, tile);
             }
         }
+
+        // The blit primitives clip against the framebuffer, not the viewport, so partial
+        // tiles on the right edge bleed into the 240..320 strip. Clear it; a real
+        // clip-rect belongs to the UI pass (see roadmap).
+        for y in 0..240usize {
+            frame[y * W + VIEW_PX as usize..y * W + W].fill(0);
+        }
     }
 }