fix: physics tick drag

TODO.md

@@ -36,7 +36,7 @@
 - ✔ Remove position pack check from trait and add to Vector
 - ❌ PIXI particles
 - ❌ Pointer events polyfill: https://github.com/jquery/PEP
-- ❌ Fix physics drag during latency
+- ✔ Fix physics drag during latency
 - ❌ Socket WebWorker can't connect in Firefox
 - ✔ PIXI update to v5
 - ❌ chunked tile communication

packages/physics/abstract/body.js

@@ -12,6 +12,7 @@ export class AbstractBody extends decorate(class {}) {
 
   constructor(world, shape) {
     super();
+    this.impulse = [0, 0];
     this.shape = shape;
     this.world = world;
   }

packages/physics/dummy/body.js

@@ -18,7 +18,6 @@ export class Body extends decorate(AbstractBody) {
   constructor(world, shape) {
     super(world, shape);
     this.force = [0, 0];
-    this.impulse = [0, 0];
     this.contacts = I.Set();
   }
 
@@ -31,10 +30,7 @@ export class Body extends decorate(AbstractBody) {
   }
 
   applyImpulse(vector) {
-    this.impulse = Vector.add(
-      this.impulse,
-      Vector.scale(vector, this.world.stepTime)
-    );
+    this.impulse = Vector.add(this.impulse, vector);
   }
 
 }

packages/physics/dummy/world.js

@@ -65,7 +65,7 @@ export class World extends AbstractWorld {
     for (const entity of this.entities.values()) {
       const body = entity.body;
       const translation = Vector.add(
-        body.impulse,
+        Vector.mul(body.impulse, elapsed),
         body.force,
       );
       body.position = Vector.add(body.position, translation);
@@ -144,7 +144,7 @@ export class World extends AbstractWorld {
       const contacts = body.contacts;
       if (contacts.size > 0) {
         const translation = Vector.add(
-          body.impulse,
+          Vector.mul(body.impulse, elapsed),
           body.force,
         );
         body.position = Vector.sub(body.position, translation);

packages/physics/matter/body.js

@@ -74,10 +74,7 @@ export class Body extends AbstractBody {
   }
 
   applyImpulse(impulse) {
-    impulse = Vector.scale(impulse, 1 / SCALE);
-    impulse = Vector.scale(impulse, this.world.stepTime);
-    const [x, y] = impulse;
-    MatterBody.translate(this.matterBody, {x, y});
+    this.impulse = Vector.add(this.impulse, Vector.scale(impulse, 1 / SCALE));
   }
 
   static bodyFromShape(shape) {

packages/physics/matter/world.js

@@ -1,4 +1,6 @@
-import {Engine, Events, World as MatterWorld} from 'matter-js';
+import {Body as MatterBody, Engine, Events, World as MatterWorld} from 'matter-js';
+
+import {Vector} from '@avocado/math';
 
 import {Body} from './body';
 import {AbstractWorld} from '../abstract/world';
@@ -62,10 +64,22 @@ export class World extends AbstractWorld {
     const stepTime = this.stepTime;
     const stepTimeInMs = stepTime * 1000;
     while (elapsed >= stepTime) {
+      // Apply impulses.
+      let it = this.entities.entries();
+      for (let value = it.next(); value.done !== true; value = it.next()) {
+        const body = value.value[0];
+        const [x, y] = Vector.scale(body.impulse, stepTime);
+        MatterBody.translate(body.matterBody, {x, y});
+      }
       Engine.update(this.engine, stepTimeInMs);
       elapsed -= stepTime;
     }
     this.elapsedRemainder = elapsed;
+    // Reset impulses.
+    const it = this.entities.entries();
+    for (let value = it.next(); value.done !== true; value = it.next()) {
+      value.value[0].impulse = [0, 0];
+    }
     // Propagate.
     super.tick(elapsed);
   }