Add chirping when pet

src/application.js

@@ -2,6 +2,7 @@ import Frame from './frame.js';
 import Layer from './layer.js';
 import Anim from './anim.js';
 import { Birb, Animations } from './birb.js';
+import { Birdsong } from './sound.js';
 import { Context, ObsidianContext } from './context.js';
 
 import {
@@ -203,6 +204,8 @@ function startApplication(birbPixels, featherPixels) {
 		FLYING: "flying",
 	};
 
+	const birdsong = new Birdsong();
+
 	let frozen = false;
 	let stateStart = Date.now();
 	let currentState = States.IDLE;
@@ -897,6 +900,7 @@ function startApplication(birbPixels, featherPixels) {
 
 	function pet() {
 		if (currentState === States.IDLE && birb.getCurrentAnimation() !== Animations.HEART) {
+			birdsong.chirp();
 			birb.setAnimation(Animations.HEART);
 			lastPetTimestamp = Date.now();
 		}

src/sound.js

@@ -0,0 +1,42 @@
+// @ts-check
+
+export class Birdsong {
+
+	/**
+	 * @type {AudioContext}
+	 */
+	audioContext;
+
+	chirp() {
+		if (!this.audioContext) {
+			this.audioContext = new AudioContext();
+		}
+
+		const TIMES = [0, 0.06, 0.16];
+		const FREQUENCIES = [2200,
+			3500 + Math.random() * 700,
+			1600 + Math.random() * 400];
+		const VOLUMES = [0.0001, 0.3, 0.0001];
+
+		const oscillator = this.audioContext.createOscillator();
+		oscillator.type = "sine";
+		const gain = this.audioContext.createGain();
+		oscillator.connect(gain);
+		gain.connect(this.audioContext.destination);
+
+		const now = this.audioContext.currentTime;
+		for (let i = 0; i < TIMES.length; i++) {
+			const time = TIMES[i] + now;
+			if (i === 0) {
+				oscillator.frequency.setValueAtTime(FREQUENCIES[i], time);
+				gain.gain.setValueAtTime(VOLUMES[i], time);
+			} else {
+				oscillator.frequency.exponentialRampToValueAtTime(FREQUENCIES[i], time);
+				gain.gain.exponentialRampToValueAtTime(VOLUMES[i], time);
+			}
+		}
+
+		oscillator.start(now);
+		oscillator.stop(now + TIMES[TIMES.length - 1]);
+	}
+}