Manually handle frameskipping for better audio on non multiple of 60hz screens (#613)

* We want to always use animation frames as our time to call the main
loop because otherwise the timing is inconsistent leading to very bad
audio.
* We don't want to call the main loop every frame otherwise > 60hz
screens will play too fast.
* We can't emscripten's frameskipping becuase it only allows for
integers whereas screeens come in many other framerates such as 75hz,
90hz, 144hz, etc.
* Therefore we manually manage frameskipping by ~~ab~~using pause and
resume game which internally just enable and disable the emscripten's
calling of the main loop. (see
27dede256b/src/platform/wasm/main.c (L183)).
* We could modify the code to let us call the main loop ourselves and
take full control over this, but for now this is okay.

website/app/src/mgba.tsx

@@ -5,10 +5,10 @@ import {
   useRef,
   useState,
 } from "react";
-import mGBA from "./vendor/mgba";
+import mGBA, { mGBAEmulator } from "./vendor/mgba";
 import { GbaKey, KeyBindings } from "./bindings";
 import { styled } from "styled-components";
-import { useSmoothedFramerate } from "./useSmoothedFramerate.hook";
+import { useFrameSkip } from "./useFrameSkip.hook";
 
 type Module = any;
 
@@ -41,18 +41,10 @@ export interface MgbaHandle {
   buttonRelease: (key: GbaKey) => void;
 }
 
-const whichFrameSkip = (frameRate: number): number | undefined => {
-  if ((frameRate + 5) % 60 <= 10) {
-    // framerate close to multiple of 60
-    // use frameskip
-    return Math.round(frameRate / 60);
-  }
-};
-
 export const Mgba = forwardRef<MgbaHandle, MgbaProps>(
   ({ gameUrl, volume, controls, paused }, ref) => {
     const canvas = useRef(null);
-    const mgbaModule = useRef<Module>({});
+    const mgbaModule = useRef<Module>({} as mGBAEmulator);
 
     const [state, setState] = useState(MgbaState.Uninitialised);
     const [gameLoaded, setGameLoaded] = useState(false);
@@ -101,23 +93,7 @@ export const Mgba = forwardRef<MgbaHandle, MgbaProps>(
         };
     }, [state]);
 
-    const frameRate = useSmoothedFramerate();
+    useFrameSkip(mgbaModule);
-    const frameSkipToUse = whichFrameSkip(frameRate);
-
-    useEffect(() => {
-      if (!gameLoaded) return;
-
-      if (frameSkipToUse) {
-        // framerate close to multiple of 60
-        // use frameskip
-        console.log("Using frameskip");
-        mgbaModule.current.setMainLoopTiming(1, frameSkipToUse);
-      } else {
-        // frame rate not close to multiple of 60, use timeout
-        console.log("Using timeout");
-        mgbaModule.current.setMainLoopTiming(0, 1000 / 59.727500569606);
-      }
-    }, [frameSkipToUse, gameLoaded]);
 
     useEffect(() => {
       if (!gameLoaded) return;

website/app/src/useFrameSkip.hook.ts

@@ -0,0 +1,54 @@
+import { MutableRefObject, useEffect } from "react";
+import { mGBAEmulator } from "./vendor/mgba";
+
+
+export const useFrameSkip = (mgbaModule: MutableRefObject<mGBAEmulator>) => {
+    useEffect(() => {
+        let previous: number | undefined = undefined;
+        let stopped = false;
+        let smoothedFrameTime = 60;
+
+        let totalTime = 0;
+        let paused = false;
+
+        const raf = (time: DOMHighResTimeStamp) => {
+            if (previous) {
+                const delta = time - previous;
+                console.log(delta);
+
+                smoothedFrameTime = (smoothedFrameTime * 3 + delta) / 4;
+
+                const smoothedFrameRate = Math.round(1 / (smoothedFrameTime / 1000));
+
+
+                totalTime += 1 / smoothedFrameRate;
+
+                if (totalTime >= 1 / 60) {
+                    totalTime -= 1 / 60;
+                    if (paused) {
+                        mgbaModule.current.resumeGame();
+                        paused = false;
+                    }
+                } else {
+                    if (!paused) {
+                        mgbaModule.current.pauseGame();
+                        paused = true;
+                    }
+                }
+
+
+            }
+            previous = time;
+
+            if (!stopped) {
+                window.requestAnimationFrame(raf);
+            }
+        }
+
+        window.requestAnimationFrame(raf);
+        return () => { stopped = true; }
+    }, [mgbaModule]);
+
+
+
+}

website/app/src/useSmoothedFramerate.hook.ts

@@ -1,35 +0,0 @@
-import { useEffect, useState } from "react";
-
-
-export const useSmoothedFramerate = (): number => {
-
-    const [smoothedFrameTime, setSmoothedFrameTime] = useState(60);
-
-    useEffect(() => {
-
-        let previous: number | undefined = undefined;
-        let stopped = false;
-
-        const raf = (time: DOMHighResTimeStamp) => {
-            if (previous) {
-                let delta = time - previous;
-
-                setSmoothedFrameTime((time) => (time * 3 + delta) / 4);
-            }
-            previous = time;
-
-
-            if (!stopped) {
-                window.requestAnimationFrame(raf);
-            }
-        }
-
-        window.requestAnimationFrame(raf);
-
-        return () => { stopped = true; }
-
-    }, []);
-
-
-    return Math.round(1 / (smoothedFrameTime / 1000));
-}