From 6d1ddf7eb13a2128d98b09380d1df36473914e84 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.

(cherry picked from commit 245c179bd31d65c6b31d156c4f6b08647df0e2fe)
---
 .../javascript/audio_driver_javascript.cpp    | 43 +++++++++++++------
 platform/javascript/audio_driver_javascript.h |  1 +
 2 files changed, 32 insertions(+), 12 deletions(-)

diff --git a/platform/javascript/audio_driver_javascript.cpp b/platform/javascript/audio_driver_javascript.cpp
index f1bc7c4382d..5a6a66c42d1 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 = NULL;
@@ -68,32 +70,32 @@ 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 */
 	EM_ASM({
-		_audioDriver_audioContext = new (window.AudioContext || window.webkitAudioContext);
+		const MIX_RATE = $0;
+		const LATENCY = $1;
+		_audioDriver_audioContext = new (window.AudioContext || window.webkitAudioContext)({ sampleRate: MIX_RATE, latencyHint: LATENCY});
 		_audioDriver_audioInput = null;
 		_audioDriver_inputStream = null;
 		_audioDriver_scriptNode = null;
-	});
+	}, mix_rate, latency);
 	/* 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 CHANNEL_COUNT = $0;
+		const BUFFER_LENGTH = $0;
+		const CHANNEL_COUNT = $1;
 
-		var channelCount = _audioDriver_audioContext.destination.channelCount;
-		try {
-			// Try letting the browser recommend a buffer length.
-			_audioDriver_scriptNode = _audioDriver_audioContext.createScriptProcessor(0, 2, channelCount);
-		} catch (e) {
-			// ...otherwise, default to 4096.
-			_audioDriver_scriptNode = _audioDriver_audioContext.createScriptProcessor(4096, 2, channelCount);
-		}
+		_audioDriver_scriptNode = _audioDriver_audioContext.createScriptProcessor(BUFFER_LENGTH, 2, CHANNEL_COUNT);
 		_audioDriver_scriptNode.connect(_audioDriver_audioContext.destination);
 
 		return _audioDriver_scriptNode.bufferSize;
-	}, channel_count);
+	}, buffer_length, channel_count);
 	/* clang-format on */
 	if (!buffer_length) {
 		return FAILED;
@@ -155,6 +157,23 @@ void AudioDriverJavaScript::resume() {
 	/* clang-format on */
 }
 
+float AudioDriverJavaScript::get_latency() {
+	/* clang-format off */
+	return EM_ASM_DOUBLE({
+		var latency = 0;
+		if (_audioDriver_audioContext) {
+			if (_audioDriver_audioContext.baseLatency) {
+				latency += _audioDriver_audioContext.baseLatency;
+			}
+			if (_audioDriver_audioContext.outputLatency) {
+				latency += _audioDriver_audioContext.outputLatency;
+			}
+		}
+		return latency;
+	});
+	/* clang-format on */
+}
+
 int AudioDriverJavaScript::get_mix_rate() const {
 
 	/* clang-format off */
diff --git a/platform/javascript/audio_driver_javascript.h b/platform/javascript/audio_driver_javascript.h
index 2bb97ba1929..229d04ea602 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();