Make FPS display look better

src/game.js

@@ -3,6 +3,8 @@ import Input from "./input.js"
 import Event from "./event.js"
 import Message from "./message.js"
 
+import { average } from "./util.js"
+
 export default class Game {
   constructor(canvas) {
     this.canvas = canvas
@@ -21,6 +23,8 @@ export default class Game {
     }
 
     this.message = null
+
+    this.fpsBuffer = [60, 60, 60, 60, 60, 60, 60, 60, 60, 60]
   }
 
   triggerEvent(eventName, object) {
@@ -45,6 +49,9 @@ export default class Game {
 
   loop(timestamp) {
     this.dt = timestamp - this.timestamp
+    const fps = 1000 / this.dt
+    this.fpsBuffer.pop()
+    this.fpsBuffer.unshift(fps)
     this.timestamp= timestamp
     this.tick(this.dt)
     this.draw()
@@ -72,11 +79,12 @@ export default class Game {
 
   drawFps(ctx) {
     ctx.fillStyle = "white"
-    ctx.fillRect(0, 0, 25, 20)
+    ctx.fillRect(ctx.canvas.width, 0, -25, 20)
     ctx.strokeStyle = "black"
     ctx.textBaseline = "top"
+    ctx.textAlign = "right"
     ctx.font = "bold 20px serif"
-    ctx.fillText(Math.round(1000 / this.dt), 0, 0)
-    ctx.strokeText(Math.round(1000 / this.dt), 0, 0)
+    ctx.fillText(Math.round(average(this.fpsBuffer)), ctx.canvas.width, 0)
+    ctx.strokeText(Math.round(average(this.fpsBuffer)), ctx.canvas.width, 0)
   }
 }

src/util.js

@@ -14,8 +14,17 @@ const doLengthsOverlap = (l1, l2) => {
   return !((l1.x + l1.width < l2.x) || (l2.x + l2.width) < l1.x)
 }
 
+function sum(array) {
+  return array.reduce((a, b) => a + b, 0)
+}
+
+function average(array) {
+  return sum(array) / array.length
+}
+
 export {
   SQRT_OF_TWO,
   isZeroVector,
-  doRectanglesOverlap
+  doRectanglesOverlap,
+  sum, average
 }