From a51f310e96a0605b25e8fb59fd0007245335d46b Mon Sep 17 00:00:00 2001
From: vkedwardli <vkedwardli@users.noreply.github.com>
Date: Thu, 26 Aug 2021 19:30:23 +0800
Subject: [PATCH] Add volume slider in audio settings (#329)

Use logarithmic volume scale
---
 core/cfg/option.cpp        |  1 +
 core/cfg/option.h          | 25 +++++++++++++++++++++++++
 core/oslib/audiostream.cpp |  4 ++--
 core/rend/gui.cpp          |  4 ++++
 4 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/core/cfg/option.cpp b/core/cfg/option.cpp
index 31399801a..8c6174183 100644
--- a/core/cfg/option.cpp
+++ b/core/cfg/option.cpp
@@ -56,6 +56,7 @@ Option<bool> AutoLatency("aica.AutoLatency",
 		);
 
 OptionString AudioBackend("backend", "auto", "audio");
+AudioVolumeOption AudioVolume;
 
 // Rendering
 
diff --git a/core/cfg/option.h b/core/cfg/option.h
index 844fd876e..40a603b0f 100644
--- a/core/cfg/option.h
+++ b/core/cfg/option.h
@@ -20,6 +20,7 @@
 #include <string>
 #include <vector>
 #include <array>
+#include <cmath>
 #include "cfg.h"
 #include "hw/maple/maple_cfg.h"
 
@@ -305,6 +306,30 @@ extern Option<bool> AutoLatency;
 
 extern OptionString AudioBackend;
 
+class AudioVolumeOption : public Option<int> {
+public:
+	AudioVolumeOption() : Option<int>("aica.Volume", 100) {};
+	float logarithmic_volume_scale = 1.0;
+
+	void load() override {
+		Option<int>::load();
+		calcDbPower();
+	}
+
+	float dbPower()
+	{
+		return logarithmic_volume_scale;
+	}
+	void calcDbPower()
+	{
+		// dB scaling calculation: https://www.dr-lex.be/info-stuff/volumecontrols.html
+		logarithmic_volume_scale = fmin(exp(4.605 * float(value) / 100.0) / 100.0, 1.0);
+		if (value < 10)
+			logarithmic_volume_scale *= value / 10.0;
+	}
+};
+extern AudioVolumeOption AudioVolume;
+
 // Rendering
 
 class RendererOption : public Option<RenderType> {
diff --git a/core/oslib/audiostream.cpp b/core/oslib/audiostream.cpp
index 506bd07a7..f638bb614 100644
--- a/core/oslib/audiostream.cpp
+++ b/core/oslib/audiostream.cpp
@@ -79,8 +79,8 @@ audiobackend_t* GetAudioBackend(const std::string& slug)
 
 void WriteSample(s16 r, s16 l)
 {
-	Buffer[writePtr].r = r;
-	Buffer[writePtr].l = l;
+	Buffer[writePtr].r = r * config::AudioVolume.dbPower();
+	Buffer[writePtr].l = l * config::AudioVolume.dbPower();
 
 	if (++writePtr == SAMPLE_COUNT)
 	{
diff --git a/core/rend/gui.cpp b/core/rend/gui.cpp
index e60685719..ffe4ace56 100644
--- a/core/rend/gui.cpp
+++ b/core/rend/gui.cpp
@@ -1558,6 +1558,10 @@ static void gui_display_settings()
 			OptionCheckbox("Disable Sound", config::DisableSound, "Disable the emulator sound output");
 			OptionCheckbox("Enable DSP", config::DSPEnabled,
 					"Enable the Dreamcast Digital Sound Processor. Only recommended on fast platforms");
+			if (OptionSlider("Volume Level", config::AudioVolume, 0, 100, "Adjust the emulator's audio level"))
+			{
+				config::AudioVolume.calcDbPower();
+			};
 #ifdef __ANDROID__
 			if (config::AudioBackend.get() == "auto" || config::AudioBackend.get() == "android")
 				OptionCheckbox("Automatic Latency", config::AutoLatency,