Added a Display struct and animation frames

vweb/src/emulator_display.jsx

@@ -1,16 +1,25 @@
-import React, { useState, useCallback, useEffect, useRef } from 'react'
-import { WasmCPU } from '../pkg/vweb.js'
+import React, { useCallback, useEffect, useRef } from 'react'
+import { WasmCPU, Display } from '../pkg/vweb.js'
 
 export default function({}) {
     const canvas = useRef(null)
-    const [ctx, setCtx] = useState(null)
-    const [cpu, _setCpu] = useState(new WasmCPU())
+    const cpu = useRef(new WasmCPU())
+    const ctx = useRef(null)
+    const display = useRef(null)
+    const request = useRef(null)
+
+    const drawFrame = useCallback(() => {
+        display.current.draw(cpu.current, ctx.current)
+        request.current = requestAnimationFrame(drawFrame)
+    }, [])
 
     useEffect(() => {
-        const c = canvas.current.getContext('2d')
-        setCtx(c)
-        cpu.draw_frame(c)
+        ctx.current = canvas.current.getContext('2d')
+        display.current = new Display()
+        request.current = requestAnimationFrame(drawFrame)
+        return () => cancelAnimationFrame(request.current)
     }, [canvas.current])
+
     return (
         <canvas ref={canvas} width={640} height={480}></canvas>
     )