From 245c179bd31d65c6b31d156c4f6b08647df0e2fe Mon Sep 17 00:00:00 2001
From: Fabio Alessandrelli <fabio.alessandrelli@gmail.com>
Date: Mon, 18 May 2020 02:19:35 +0200
Subject: [PATCH] AudioDriverJavaScript now compute buffer size.

Based on mix rate and expected latency.
---
 .../javascript/audio_driver_javascript.cpp    | 47 +++++++++++++------
 platform/javascript/audio_driver_javascript.h |  1 +
 2 files changed, 34 insertions(+), 14 deletions(-)

diff --git a/platform/javascript/audio_driver_javascript.cpp b/platform/javascript/audio_driver_javascript.cpp
index 03ca5f78d16..808260a3856 100644
--- a/platform/javascript/audio_driver_javascript.cpp
+++ b/platform/javascript/audio_driver_javascript.cpp
@@ -30,6 +30,8 @@
 
 #include "audio_driver_javascript.h"
 
+#include "core/project_settings.h"
+
 #include <emscripten.h>
 
 AudioDriverJavaScript *AudioDriverJavaScript::singleton = nullptr;
@@ -62,10 +64,15 @@ void AudioDriverJavaScript::process_capture(float sample) {
 }
 
 Error AudioDriverJavaScript::init() {
+	int mix_rate = GLOBAL_DEF_RST("audio/mix_rate", DEFAULT_MIX_RATE);
+	int latency = GLOBAL_DEF_RST("audio/output_latency", DEFAULT_OUTPUT_LATENCY);
+
 	/* clang-format off */
 	_driver_id = EM_ASM_INT({
+		const MIX_RATE = $0;
+		const LATENCY = $1;
 		return Module.IDHandler.add({
-			'context': new (window.AudioContext || window.webkitAudioContext),
+			'context': new (window.AudioContext || window.webkitAudioContext)({ sampleRate: MIX_RATE, latencyHint: LATENCY}),
 			'input': null,
 			'stream': null,
 			'script': null
@@ -74,26 +81,19 @@ Error AudioDriverJavaScript::init() {
 	/* clang-format on */
 
 	int channel_count = get_total_channels_by_speaker_mode(get_speaker_mode());
+	buffer_length = closest_power_of_2((latency * mix_rate / 1000) * channel_count);
 	/* clang-format off */
 	buffer_length = EM_ASM_INT({
 		var ref = Module.IDHandler.get($0);
-		var ctx = ref['context'];
-		var CHANNEL_COUNT = $1;
+		const ctx = ref['context'];
+		const BUFFER_LENGTH = $1;
+		const CHANNEL_COUNT = $2;
 
-		var channelCount = ctx.destination.channelCount;
-		var script = null;
-		try {
-			// Try letting the browser recommend a buffer length.
-			script = ctx.createScriptProcessor(0, 2, channelCount);
-		} catch (e) {
-			// ...otherwise, default to 4096.
-			script = ctx.createScriptProcessor(4096, 2, channelCount);
-		}
+		var script = ctx.createScriptProcessor(BUFFER_LENGTH, 2, CHANNEL_COUNT);
 		script.connect(ctx.destination);
 		ref['script'] = script;
-
 		return script.bufferSize;
-	}, _driver_id, channel_count);
+	}, _driver_id, buffer_length, channel_count);
 	/* clang-format on */
 	if (!buffer_length) {
 		return FAILED;
@@ -156,6 +156,25 @@ void AudioDriverJavaScript::resume() {
 	/* clang-format on */
 }
 
+float AudioDriverJavaScript::get_latency() {
+	/* clang-format off */
+	return EM_ASM_DOUBLE({
+		const ref = Module.IDHandler.get($0);
+		var latency = 0;
+		if (ref && ref['context']) {
+			const ctx = ref['context'];
+			if (ctx.baseLatency) {
+				latency += ctx.baseLatency;
+			}
+			if (ctx.outputLatency) {
+				latency += ctx.outputLatency;
+			}
+		}
+		return latency;
+	}, _driver_id);
+	/* clang-format on */
+}
+
 int AudioDriverJavaScript::get_mix_rate() const {
 	/* clang-format off */
 	return EM_ASM_INT({
diff --git a/platform/javascript/audio_driver_javascript.h b/platform/javascript/audio_driver_javascript.h
index 7d5237998ad..9b26be001e0 100644
--- a/platform/javascript/audio_driver_javascript.h
+++ b/platform/javascript/audio_driver_javascript.h
@@ -50,6 +50,7 @@ public:
 	virtual Error init();
 	virtual void start();
 	void resume();
+	virtual float get_latency();
 	virtual int get_mix_rate() const;
 	virtual SpeakerMode get_speaker_mode() const;
 	virtual void lock();