Change how ticking works

client/camera.ts

@@ -14,10 +14,11 @@ export class Camera {
 	near = 0.1;
 	far = 1000;
 
-	setup(entity: Entity) {
-		this.x = entity.x;
-		this.y = entity.y + entity.eye_height;
-		this.z = entity.z;
+	setup(entity: Entity, partial_tick: number) {
+		const { x, y, z } = entity.render_position(partial_tick);
+		this.x = x;
+		this.y = y + entity.eye_height;
+		this.z = z;
 		this.yaw = entity.yaw;
 		this.pitch = entity.pitch;
 	}

client/client.ts

@@ -15,9 +15,13 @@ import { InputManager } from "./input_manager.ts";
 import { Connection } from "./network.ts";
 import { canvas, resize_canvas } from "./renderer/mod.ts";
 import { show_fatal_error } from "./fatal.ts";
+import { TICK_DELTA } from "$/common/constants.ts";
 
-// the game client, like minecraft's Minecraft class: owns the level, the player, the screens and the renderer,
-// and runs one step of the game every frame
+// after a long stall (a hidden tab, a debugger) the game skips ahead instead of running every missed tick at once
+const MAX_TICKS_PER_FRAME = 10;
+
+// the game client, like minecraft's Minecraft class: owns the level, the player, the screens and the renderer.
+// the game runs in fixed ticks (TICKS_PER_SECOND), input and drawing happen every frame
 export class Client {
 	connection: Connection;
 	options = new Options();
@@ -35,6 +39,12 @@ export class Client {
 	hit_result: BlockHitResult | undefined;
 	debugging = false;
 
+	// seconds of game time not ticked yet
+	#pending_time = 0;
+	// whether the attack button is held on a block, breaking it advances every tick
+	#attacking = false;
+	#stopped = false;
+
 	constructor(connection: Connection) {
 		this.connection = connection;
 
@@ -74,24 +84,46 @@ export class Client {
 		this.screens.pop()?.on_close();
 	}
 
-	// one frame: network, input, the level and its entities, then drawing
+	// one frame: input, as many ticks as are due, then drawing between the last tick and the next
 	run_frame(delta: number) {
+		this.screen?.on_tick(delta);
+		this.#handle_keybinds();
+
+		this.#pending_time += delta;
+		let ticks = 0;
+		while (this.#pending_time >= TICK_DELTA && ticks < MAX_TICKS_PER_FRAME) {
+			this.tick();
+			if (this.#stopped) {
+				return;
+			}
+			this.#pending_time -= TICK_DELTA;
+			ticks += 1;
+		}
+		if (ticks === MAX_TICKS_PER_FRAME) {
+			this.#pending_time = Math.min(this.#pending_time, TICK_DELTA);
+		}
+
+		this.game_renderer.render(this, this.#pending_time / TICK_DELTA);
+	}
+
+	// one step of the game: what the server sent, breaking, chunk loading, then every entity
+	tick() {
 		this.packet_listener.handle_packets();
 		if (this.connection.closed) {
 			show_fatal_error("Lost connection to the server");
+			this.#stopped = true;
 			return;
 		}
 
-		this.screen?.on_tick(delta);
-		this.#handle_keybinds(delta);
-
-		this.level.update_loaded_chunks(this.player.x, this.player.z, this.options.render_distance);
-		this.level.tick(delta);
-
-		this.game_renderer.render(this);
+		if (this.#attacking && this.hit_result) {
+			this.game_mode.continue_destroy_block(this.hit_result);
 		}
 
-	#handle_keybinds(delta: number) {
+		this.level.update_loaded_chunks(this.player.x, this.player.z, this.options.render_distance);
+		this.level.tick();
+	}
+
+	#handle_keybinds() {
 		const options = this.options;
 		const player = this.player;
 
@@ -122,16 +154,18 @@ export class Client {
 		InputManager.set_mouse_grabbed(!this.screen);
 
 		this.hit_result = this.level.pick(player.x, player.y + player.eye_height, player.z, player.yaw, player.pitch);
-		this.#handle_block_interaction(delta);
+		this.#handle_block_interaction();
 
 		if (!this.screen) {
 			this.#handle_hotbar();
 		}
 	}
 
-	#handle_block_interaction(delta: number) {
+	// clicks happen right away, holding to break advances in tick()
+	#handle_block_interaction() {
 		const hit = this.hit_result;
 		const attacking = !this.screen && InputManager.is_mouse_down(0);
+		this.#attacking = attacking;
 
 		if (!attacking || !hit) {
 			this.game_mode.stop_destroy_block();
@@ -144,9 +178,7 @@ export class Client {
 			if (InputManager.is_mouse_pressed(0)) {
 				this.game_mode.start_destroy_block(hit);
 			}
-			if (attacking) {
-				this.game_mode.continue_destroy_block(hit, delta);
-			} else if (InputManager.is_mouse_pressed(2)) {
+			if (!attacking && InputManager.is_mouse_pressed(2)) {
 				this.game_mode.use_item_on(hit);
 			}
 		} else if (InputManager.is_mouse_pressed(2)) {

client/entity/entity.ts

@@ -1,6 +1,13 @@
+import { TICK_DELTA } from "$/common/constants.ts";
 import type { ClientLevel } from "../level/client_level.ts";
 
-// anything that exists in the level and moves, like minecraft's Entity. position is the middle of its feet
+// how far inside a block face still counts as touching it, so boxes resting exactly on a face don't snag
+const EPSILON = 1e-7;
+// the two axes that aren't the one being moved along
+const OTHER_AXES = [[1, 2], [0, 2], [0, 1]] as const;
+
+// anything that exists in the level and moves, like minecraft's Entity. position is the middle of its feet.
+// it's simulated in fixed ticks (common/constants.ts), frames draw it between its last two positions
 export abstract class Entity {
 	id: string;
 	level: ClientLevel;
@@ -8,6 +15,10 @@ export abstract class Entity {
 	x = 0;
 	y = 0;
 	z = 0;
+	// where it was at the start of the tick, what frames interpolate from
+	prev_x = 0;
+	prev_y = 0;
+	prev_z = 0;
 	// blocks per second
 	vx = 0;
 	vy = 0;
@@ -39,62 +50,92 @@ export abstract class Entity {
 		return this.colliding_y === 1;
 	}
 
+	// jumps there, without interpolating from where it was
 	set_position(x: number, y: number, z: number) {
-		this.x = x;
-		this.y = y;
-		this.z = z;
+		this.x = this.prev_x = x;
+		this.y = this.prev_y = y;
+		this.z = this.prev_z = z;
 	}
 
-	abstract tick(delta: number): void;
-
-	// falls and moves by its velocity, stopping on each axis it would run into a block on
-	move(delta: number) {
-		this.vy += this.gravity * delta;
-
-		this.colliding_x = this.vx !== 0 && this.#collides(this.x + this.vx * delta, this.y, this.z)
-			? -Math.sign(this.vx)
-			: 0;
-		if (this.colliding_x !== 0) {
-			this.vx = 0;
+	save_previous_position() {
+		this.prev_x = this.x;
+		this.prev_y = this.y;
+		this.prev_z = this.z;
 	}
 
-		this.colliding_y = this.vy !== 0 && this.#collides(this.x, this.y + this.vy * delta, this.z)
-			? -Math.sign(this.vy)
-			: 0;
-		if (this.colliding_y !== 0) {
-			this.vy = 0;
+	// where to draw it, partial_tick is how far the frame is between the last tick and the next
+	render_position(partial_tick: number) {
+		return {
+			x: this.prev_x + (this.x - this.prev_x) * partial_tick,
+			y: this.prev_y + (this.y - this.prev_y) * partial_tick,
+			z: this.prev_z + (this.z - this.prev_z) * partial_tick,
+		};
 	}
 
-		this.colliding_z = this.vz !== 0 && this.#collides(this.x, this.y, this.z + this.vz * delta)
-			? -Math.sign(this.vz)
-			: 0;
-		if (this.colliding_z !== 0) {
-			this.vz = 0;
+	// one step of the game, TICK_DELTA seconds
+	abstract tick(): void;
+
+	// falls and moves by its velocity for one tick. like minecraft it moves along y, then x, then z, each time only
+	// as far as it can before touching a block, and stops its velocity on the axes it hit something
+	move() {
+		// the average of this tick's start and end speed, so the arc is the same at any tick rate
+		const wanted_y = (this.vy + this.gravity * TICK_DELTA / 2) * TICK_DELTA;
+		this.vy += this.gravity * TICK_DELTA;
+		const wanted = [this.vx * TICK_DELTA, wanted_y, this.vz * TICK_DELTA];
+
+		const half = this.width / 2;
+		const min = [this.x - half, this.y, this.z - half];
+		const max = [this.x + half, this.y + this.height, this.z + half];
+		const moved = [0, 0, 0];
+		for (const axis of [1, 0, 2]) {
+			const distance = this.#clip(min, max, axis, wanted[axis]);
+			min[axis] += distance;
+			max[axis] += distance;
+			moved[axis] = distance;
 		}
 
-		this.x += this.vx * delta;
-		this.y += this.vy * delta;
-		this.z += this.vz * delta;
+		const hit = (axis: number) => moved[axis] !== wanted[axis] ? -Math.sign(wanted[axis]) : 0;
+		this.colliding_x = hit(0);
+		this.colliding_y = hit(1);
+		this.colliding_z = hit(2);
+		if (this.colliding_x !== 0) this.vx = 0;
+		if (this.colliding_y !== 0) this.vy = 0;
+		if (this.colliding_z !== 0) this.vz = 0;
+
+		this.x += moved[0];
+		this.y += moved[1];
+		this.z += moved[2];
 	}
 
-	// whether the collision box at x/y/z overlaps any block, unloaded chunks included
-	#collides(x: number, y: number, z: number) {
-		const min_x = Math.floor(x - this.width / 2);
-		const max_x = Math.floor(x + this.width / 2);
-		const min_y = Math.floor(y);
-		const max_y = Math.floor(y + this.height);
-		const min_z = Math.floor(z - this.width / 2);
-		const max_z = Math.floor(z + this.width / 2);
+	// how far the box can go along an axis before it runs into a block, unloaded chunks included.
+	// blocks it's already inside don't stop it, so it can get out of them
+	#clip(min: number[], max: number[], axis: number, distance: number) {
+		if (distance === 0) {
+			return 0;
+		}
 
-		for (let bx = min_x; bx <= max_x; bx++) {
-			for (let by = min_y; by <= max_y; by++) {
-				for (let bz = min_z; bz <= max_z; bz++) {
-					if (this.level.get_block(bx, by, bz)) {
-						return true;
+		const [a, b] = OTHER_AXES[axis];
+		const from = Math.floor(Math.min(min[axis], min[axis] + distance));
+		const to = Math.floor(Math.max(max[axis], max[axis] + distance));
+		const position = [0, 0, 0];
+
+		for (let i = from; i <= to; i++) {
+			for (let j = Math.floor(min[a] + EPSILON); j <= Math.floor(max[a] - EPSILON); j++) {
+				for (let k = Math.floor(min[b] + EPSILON); k <= Math.floor(max[b] - EPSILON); k++) {
+					position[axis] = i;
+					position[a] = j;
+					position[b] = k;
+					if (!this.level.get_block(position[0], position[1], position[2])) {
+						continue;
+					}
+					if (distance > 0 && i >= max[axis] - EPSILON) {
+						distance = Math.min(distance, i - max[axis]);
+					} else if (distance < 0 && i + 1 <= min[axis] + EPSILON) {
+						distance = Math.max(distance, i + 1 - min[axis]);
 					}
 				}
 			}
 		}
-		return false;
+		return distance;
 	}
 }

client/entity/local_player.ts

@@ -3,8 +3,8 @@ import { InputManager } from "../input_manager.ts";
 import { ClientInventories } from "../inventory.ts";
 import { Player } from "./player.ts";
 
-// how often the position goes to the server
-const SEND_POSITION_INTERVAL = 1 / 10;
+// the position goes to the server every other tick
+const SEND_POSITION_TICKS = 2;
 
 // the player this client controls, like minecraft's LocalPlayer
 export class LocalPlayer extends Player {
@@ -14,22 +14,22 @@ export class LocalPlayer extends Player {
 	move_speed = 4;
 	jump_force = 6.7;
 
-	#send_timer = 0;
+	#ticks_since_sent = 0;
 
 	constructor(client: Client, id: string, name: string) {
 		super(client.level, id, name);
 		this.client = client;
 	}
 
-	tick(delta: number) {
+	tick() {
 		if (!this.client.screen) {
 			this.#apply_input();
 		}
-		this.move(delta);
-		this.#send_position(delta);
+		this.move();
+		this.#send_position();
 	}
 
-	// turns with the mouse, like minecraft's MouseHandler.turnPlayer
+	// turns with the mouse every frame, not every tick, like minecraft's MouseHandler.turnPlayer
 	turn(mouse_dx: number, mouse_dy: number) {
 		this.yaw += -mouse_dx * 0.001;
 		this.pitch += -mouse_dy * 0.001;
@@ -75,12 +75,12 @@ export class LocalPlayer extends Player {
 		}
 	}
 
-	#send_position(delta: number) {
-		this.#send_timer += delta;
-		if (this.#send_timer < SEND_POSITION_INTERVAL) {
+	#send_position() {
+		this.#ticks_since_sent += 1;
+		if (this.#ticks_since_sent < SEND_POSITION_TICKS) {
 			return;
 		}
-		this.#send_timer = 0;
+		this.#ticks_since_sent = 0;
 		this.client.connection.send({
 			type: "move",
 			x: this.x,

client/entity/remote_player.ts

@@ -1,4 +1,5 @@
 import type { PlayerInfo } from "$/common/protocol.ts";
+import { TICK_DELTA } from "$/common/constants.ts";
 import type { ClientLevel } from "../level/client_level.ts";
 import { Player } from "./player.ts";
 
@@ -32,8 +33,8 @@ export class RemotePlayer extends Player {
 		this.pitch = pitch;
 	}
 
-	tick(delta: number) {
-		const t = Math.min(1, delta * SMOOTHING);
+	tick() {
+		const t = Math.min(1, TICK_DELTA * SMOOTHING);
 		this.x += (this.target_x - this.x) * t;
 		this.y += (this.target_y - this.y) * t;
 		this.z += (this.target_z - this.z) * t;

client/game_mode.ts

@@ -1,5 +1,5 @@
 import { BlockRegistry, EverythingRegistry, ItemRegistry } from "$/common/everything_registry.ts";
-import { AIR, FACE_OFFSETS } from "$/common/constants.ts";
+import { AIR, FACE_OFFSETS, TICK_DELTA } from "$/common/constants.ts";
 import type { Client } from "./client.ts";
 import type { BlockHitResult } from "./level/client_level.ts";
 
@@ -22,14 +22,14 @@ export class MultiPlayerGameMode {
 		this.client.connection.send({ type: "hit_block", x: hit.x, y: hit.y, z: hit.z });
 	}
 
-	// called every frame the attack button is held on a block
-	continue_destroy_block(hit: BlockHitResult, delta: number) {
+	// called every tick the attack button is held on a block
+	continue_destroy_block(hit: BlockHitResult) {
 		const block_info = EverythingRegistry.get_by_id<BlockRegistry>("blocks", hit.block)!;
 		const tool_type = this.#held_item()?.tool_type;
 
 		this.destroy_pos = { x: hit.x, y: hit.y, z: hit.z };
 		this.destroy_time = block_info.toughness ?? 9999;
-		this.destroy_progress += delta * (tool_type === block_info.tool_to_break ? 2 : 1);
+		this.destroy_progress += TICK_DELTA * (tool_type === block_info.tool_to_break ? 2 : 1);
 
 		if (this.destroy_progress >= this.destroy_time) {
 			// show it right away, the server decides drops and corrects us if it disagrees

client/level/client_level.ts

@@ -123,9 +123,10 @@ export class ClientLevel {
 		this.entities.delete(id);
 	}
 
-	tick(delta: number) {
+	tick() {
 		for (const entity of this.entities.values()) {
-			entity.tick(delta);
+			entity.save_previous_position();
+			entity.tick();
 		}
 	}
 

client/rendering/game_renderer.ts

@@ -10,14 +10,15 @@ export class GameRenderer {
 	hud = new Hud();
 	debug_overlay = new DebugOverlay();
 
-	render(client: Client) {
+	// partial_tick is how far this frame is between the last tick and the next, entities are drawn in between
+	render(client: Client, partial_tick: number) {
 		const camera = client.camera;
-		camera.setup(client.player);
+		camera.setup(client.player, partial_tick);
 
 		begin_mode_3d(camera);
 		this.level_renderer.render_opaque(client.level, camera);
 		this.level_renderer.render_destroy_progress(client.game_mode);
-		this.level_renderer.render_entities(client.level, client.player);
+		this.level_renderer.render_entities(client.level, client.player, partial_tick);
 		this.level_renderer.render_translucent(client.level, camera);
 		end_mode_3d();
 

client/rendering/level_renderer.ts

@@ -75,13 +75,13 @@ export class LevelRenderer {
 	}
 
 	// every entity but the one the camera is in
-	render_entities(level: ClientLevel, camera_entity: Entity) {
+	render_entities(level: ClientLevel, camera_entity: Entity, partial_tick: number) {
 		flush_batch();
 		set_current_texture(white_tex!);
 
 		for (const entity of level.entities.values()) {
 			if (entity !== camera_entity && entity instanceof RemotePlayer) {
-				render_player(entity);
+				render_player(entity, partial_tick);
 			}
 		}
 
@@ -119,9 +119,9 @@ export class LevelRenderer {
 }
 
 // a box body and head in the player's color
-function render_player(player: RemotePlayer) {
+function render_player(player: RemotePlayer, partial_tick: number) {
 	const [r, g, b] = player.color;
-	const { x, y, z } = player;
+	const { x, y, z } = player.render_position(partial_tick);
 
 	// body
 	push_box(x - 0.3, y, z - 0.15, 0.6, 1.3, 0.3, r, g, b);