From 3b88ab89695624f6bd39ce5d7b18b41c2621bac8 Mon Sep 17 00:00:00 2001
From: cha0s <git@cha0s.io>
Date: Fri, 6 Sep 2024 19:21:58 -0500
Subject: [PATCH] perf: smoother interpolation

---
 app/client/interpolator.js | 135 +++++++++++++++++--------------------
 1 file changed, 60 insertions(+), 75 deletions(-)

diff --git a/app/client/interpolator.js b/app/client/interpolator.js
index 0b29b7a..fb32346 100644
--- a/app/client/interpolator.js
+++ b/app/client/interpolator.js
@@ -1,47 +1,27 @@
-export default class Interpolator {
-  duration = 0;
-  latest = null;
-  location = 0;
-  penultimate;
-  tracking = [];
-  accept(state) {
-    const packet = state;
-    if ('Tick' !== packet.type) {
+let authoritative = [];
+let duration = 0;
+let last = performance.now();
+let latest = null;
+let location = 0;
+let penultimate;
+let tracking = [];
+
+const interpolate = () => {
+  const now = performance.now();
+  const elapsed = (now - last) / 1000;
+  last = now;
+  if (authoritative.length > 0) {
+    for (const packet of authoritative) {
       postMessage(packet);
-      return;
     }
-    this.penultimate = this.latest;
-    this.latest = packet;
-    this.tracking = [];
-    if (this.penultimate) {
-      this.duration = this.penultimate.payload.elapsed;
-      const [from, to] = [this.penultimate.payload.ecs, this.latest.payload.ecs];
-      for (const entityId in from) {
-        for (const componentName in from[entityId]) {
-          if (
-            ['Camera', 'Position'].includes(componentName)
-            && to[entityId]?.[componentName]
-          ) {
-            this.tracking.push({
-              entityId,
-              componentName,
-              properties: ['x', 'y'],
-            });
-          }
-        }
-      }
-    }
-    this.location = 0;
+    authoritative = [];
   }
-  interpolate(elapsed) {
-    if (0 === this.tracking.length) {
-      return undefined;
-    }
-    this.location += elapsed;
-    const fraction = Math.min(1, this.location / this.duration);
-    const [from, to] = [this.penultimate.payload.ecs, this.latest.payload.ecs];
+  if (tracking.length > 0) {
+    location += elapsed;
+    const fraction = location / duration;
+    const [from, to] = [penultimate.payload.ecs, latest.payload.ecs];
     const interpolated = {};
-    for (const {entityId, componentName, properties} of this.tracking) {
+    for (const {entityId, componentName, properties} of tracking) {
       if (!interpolated[entityId]) {
         interpolated[entityId] = {};
       }
@@ -64,61 +44,66 @@ export default class Interpolator {
         );
       }
     }
-    return {
+    postMessage({
       type: 'Tick',
       payload: {
+        ...penultimate.payload,
         ecs: interpolated,
         elapsed,
-        frame: this.penultimate.payload.frame + fraction,
+        frame: penultimate.payload.frame + fraction,
       },
-    };
-  }
-}
-
-let handle;
-const interpolator = new Interpolator();
-let last;
-
-const interpolate = (now) => {
-  const elapsed = (now - last) / 1000;
-  last = now;
-  const interpolated = interpolator.interpolate(elapsed);
-  if (interpolated) {
-    handle = requestAnimationFrame(interpolate);
-    postMessage(interpolated);
-  }
-  else {
-    handle = null;
+    });
   }
+  requestAnimationFrame(interpolate);
 }
+requestAnimationFrame(interpolate);
 
 onmessage = async (event) => {
-  interpolator.accept(event.data);
-  switch (event.data.type) {
+  const packet = event.data;
+  switch (packet.type) {
     case 'EcsChange': {
-      if (handle) {
-        cancelAnimationFrame(handle)
-        handle = null;
-      }
-      interpolator.latest = null;
+      authoritative = [];
+      latest = null;
+      tracking = [];
+      postMessage(packet);
       break;
     }
     case 'Tick': {
-      if (interpolator.penultimate) {
-        postMessage({
+      penultimate = latest;
+      latest = packet;
+      if (penultimate) {
+        duration = penultimate.payload.elapsed;
+        location = 0;
+        tracking = [];
+        const [from, to] = [penultimate.payload.ecs, latest.payload.ecs];
+        for (const entityId in from) {
+          for (const componentName in from[entityId]) {
+            if (
+              ['Camera', 'Position'].includes(componentName)
+              && to[entityId]?.[componentName]
+            ) {
+              tracking.push({
+                entityId,
+                componentName,
+                properties: ['x', 'y'],
+              });
+            }
+          }
+        }
+        authoritative.push({
           type: 'Tick',
           payload: {
-            ecs: interpolator.penultimate.payload.ecs,
+            ...penultimate.payload,
             elapsed: last ? (performance.now() - last) / 1000 : 0,
-            frame: interpolator.penultimate.payload.frame,
           },
         });
-        if (!handle) {
-          last = performance.now();
-          handle = requestAnimationFrame(interpolate);
-        }
+        last = performance.now();
       }
       break;
     }
+    default: {
+      postMessage(packet);
+      break;
+    }
   }
 };