Add the "channels" configuration option for setting channel counts.

Closes #25.

CONFIGURATION.md

@@ -40,6 +40,10 @@ device = ""
 # PortAudioDevices program.
 device = "Speakers (Realtek High Definition Audio)"
 
+# Open the hardware output device with 6 channels. This is only required if you
+# are unhappy with the default channel count.
+channels = 6
+
 # Set the output to WASAPI Exclusive Mode.
 wasapiExclusiveMode = true
 ```
@@ -122,6 +126,44 @@ The default behaviour is to use the default device for the selected backend.
 `PortAudioDevices` will show which device that is. Typically, this would be the
 device set as default in the Windows audio control panel.
 
+#### Option `channels`
+
+*Integer*-typed option that determines how many channels FlexASIO will open the
+hardware audio device with. This is the number of channels the ASIO Host
+Application will see.
+
+**Note:** even if the ASIO Host Application only decides to use a subset of the
+available channels, the hardware audio device will still be opened with the
+number of channels configured here. In other words, the host application has no
+control over the hardware channel configuration.
+
+If the requested channel count doesn't match what the audio device is configured
+for, the resulting behaviour depends on the backend. Some backends will accept
+any channel count, upmixing or downmixing as necessary. Other backends might
+refuse to initialize.
+
+The value of this option must be strictly positive. To completely disable the
+input or output, set the `device` option to the empty string (see above).
+
+**Note:** with the WASAPI backend, setting this option has the side effect of
+disabling channel masks. This means channel names will not be shown, and the
+backend might behave differently with regard to channel routing.
+
+Example:
+
+```toml
+[input]
+channels = 2
+
+[output]
+channels = 6
+```
+
+The default behaviour is to use the maximum channel count for the selected
+device as reported by PortAudio. This information is shown in the output of the
+`PortAudioDevice` program. Sadly, PortAudio often gets the channel count wrong,
+so setting this option explicitly might be necessary for correct operation.
+
 #### Option `wasapiExclusiveMode`
 
 *Boolean*-typed option that determines if the stream should be opened in

FlexASIO/config.cpp

@@ -72,14 +72,23 @@ namespace flexasio {
 		template <typename T> struct RemoveOptional { using Value = T; };
 		template <typename T> struct RemoveOptional<std::optional<T>> { using Value = T; };
 
-		template <typename T> void SetOption(const toml::Table& table, const std::string& key, T& option) {
+		template <typename T, typename Validator> void SetOption(const toml::Table& table, const std::string& key, T& option, Validator validator) {
 			ProcessTypedOption<RemoveOptional<T>::Value>(table, key, [&](const RemoveOptional<T>::Value& value) {
+				validator(value);
 				option = value;
 			});
 		}
+		template <typename T> void SetOption(const toml::Table& table, const std::string& key, T& option) {
+			return SetOption(table, key, option, [](const T&) {});
+		}
+
+		void ValidateChannelCount(const int& channelCount) {
+			if (channelCount <= 0) throw std::runtime_error("channel count must be strictly positive - to disable a stream direction, set the 'device' option to the empty string \"\" instead");
+		}
 
 		void SetStream(const toml::Table& table, Config::Stream& stream) {
 			SetOption(table, "device", stream.device);
+			SetOption(table, "channels", stream.channels, ValidateChannelCount);
 			SetOption(table, "wasapiExclusiveMode", stream.wasapiExclusiveMode);
 		}
 

FlexASIO/config.h

@@ -10,6 +10,7 @@ namespace flexasio {
 
 		struct Stream {
 			std::optional<std::string> device;
+			std::optional<int> channels;
 			bool wasapiExclusiveMode = false;
 		};
 		Stream input;

FlexASIO/flexasio.cpp

@@ -214,7 +214,35 @@ namespace flexasio {
 
 		if (!inputDevice.has_value() && !outputDevice.has_value()) throw ASIOException(ASE_HWMalfunction, "No usable input nor output devices");
 
-		Log() << "Channel count: " << GetInputChannelCount() << " input, " << GetOutputChannelCount() << " output";
+		Log() << "Input channel count: " << GetInputChannelCount() << " mask: " << GetWaveFormatChannelMaskString(GetInputChannelMask());
+		if (inputDevice.has_value() && GetInputChannelCount() > inputDevice->info.maxInputChannels)
+			Log() << "WARNING: input channel count is higher than the max channel count for this device. Input device initialization might fail.";
+
+		Log() << "Output channel count: " << GetOutputChannelCount() << " mask: " << GetWaveFormatChannelMaskString(GetOutputChannelMask());
+		if (outputDevice.has_value() && GetOutputChannelCount() > outputDevice->info.maxOutputChannels)
+			Log() << "WARNING: output channel count is higher than the max channel count for this device. Output device initialization might fail.";
+	}
+
+	int FlexASIO::GetInputChannelCount() const {
+		if (!inputDevice.has_value()) return 0;
+		if (config.input.channels.has_value()) return *config.input.channels;
+		return inputDevice->info.maxInputChannels;
+	}
+	int FlexASIO::GetOutputChannelCount() const {
+		if (!outputDevice.has_value()) return 0;
+		if (config.output.channels.has_value()) return *config.output.channels;
+		return outputDevice->info.maxOutputChannels;
+	}
+
+	DWORD FlexASIO::GetInputChannelMask() const {
+		if (!inputFormat.has_value()) return 0;
+		if (config.input.channels.has_value()) return 0;
+		return inputFormat->dwChannelMask;
+	}
+	DWORD FlexASIO::GetOutputChannelMask() const {
+		if (!outputFormat.has_value()) return 0;
+		if (config.output.channels.has_value()) return 0;
+		return outputFormat->dwChannelMask;
 	}
 
 	void FlexASIO::GetChannels(long* numInputChannels, long* numOutputChannels)

FlexASIO/flexasio.h

@@ -139,10 +139,10 @@ namespace flexasio {
 			std::optional<RunningState> runningState;
 		};
 
-		int GetInputChannelCount() const { return inputDevice.has_value() ? inputDevice->info.maxInputChannels : 0; }
-		int GetOutputChannelCount() const { return outputDevice.has_value() ? outputDevice->info.maxOutputChannels : 0; }
-		DWORD GetInputChannelMask() const { return inputFormat.has_value() ? inputFormat->dwChannelMask : 0; }
-		DWORD GetOutputChannelMask() const { return outputFormat.has_value() ? outputFormat->dwChannelMask : 0; }
+		int GetInputChannelCount() const;
+		int GetOutputChannelCount() const;
+		DWORD GetInputChannelMask() const;
+		DWORD GetOutputChannelMask() const;
 
 		Stream OpenStream(double sampleRate, unsigned long framesPerBuffer, PaStreamCallback callback, void* callbackUserData);
 

FlexASIOUtil/portaudio.cpp

@@ -204,58 +204,54 @@ namespace flexasio {
 		return format;
 	}
 
-	namespace {
-
-		std::string GetWaveFormatTagString(WORD formatTag) {
-			return EnumToString(formatTag, {
-				{ WAVE_FORMAT_EXTENSIBLE, "EXTENSIBLE" },
-				{ WAVE_FORMAT_MPEG, "MPEG" },
-				{ WAVE_FORMAT_MPEGLAYER3, "MPEGLAYER3" },
-				});
-		}
-
-		std::string GetWaveFormatChannelMaskString(DWORD channelMask) {
-			return BitfieldToString(channelMask, {
-				{SPEAKER_FRONT_LEFT, "Front Left"},
-				{SPEAKER_FRONT_RIGHT, "Front Right"},
-				{SPEAKER_FRONT_CENTER, "Front Center"},
-				{SPEAKER_LOW_FREQUENCY, "Low Frequency"},
-				{SPEAKER_BACK_LEFT, "Back Left"},
-				{SPEAKER_BACK_RIGHT, "Back Right"},
-				{SPEAKER_FRONT_LEFT_OF_CENTER, "Front Left of Center"},
-				{SPEAKER_FRONT_RIGHT_OF_CENTER, "Front Right of Center"},
-				{SPEAKER_BACK_CENTER, "Back Center"},
-				{SPEAKER_SIDE_LEFT, "Side Left"},
-				{SPEAKER_SIDE_RIGHT, "Side Right"},
-				{SPEAKER_TOP_CENTER, "Top Center"},
-				{SPEAKER_TOP_FRONT_LEFT, "Top Front Left"},
-				{SPEAKER_TOP_FRONT_CENTER, "Top Front Center"},
-				{SPEAKER_TOP_FRONT_RIGHT, "Top Front Right"},
-				{SPEAKER_TOP_BACK_LEFT, "Top Back Left"},
-				{SPEAKER_TOP_BACK_CENTER, "Top Back Center"},
-				{SPEAKER_TOP_BACK_RIGHT, "Top Back Right"},
-				});
-		}
+	std::string GetWaveFormatTagString(WORD formatTag) {
+		return EnumToString(formatTag, {
+			{ WAVE_FORMAT_EXTENSIBLE, "EXTENSIBLE" },
+			{ WAVE_FORMAT_MPEG, "MPEG" },
+			{ WAVE_FORMAT_MPEGLAYER3, "MPEGLAYER3" },
+			});
+	}
 
-		std::string GetWaveSubFormatString(const GUID& subFormat) {
-			return EnumToString(subFormat, {
-				{ KSDATAFORMAT_SUBTYPE_ADPCM, "ADPCM" },
-				{ KSDATAFORMAT_SUBTYPE_ALAW, "A-law" },
-				{ KSDATAFORMAT_SUBTYPE_DRM, "DRM" },
-				{ KSDATAFORMAT_SUBTYPE_IEC61937_DOLBY_DIGITAL_PLUS, "IEC61937 Dolby Digital Plus" },
-				{ KSDATAFORMAT_SUBTYPE_IEC61937_DOLBY_DIGITAL, "IEC61937 Dolby Digital" },
-				{ KSDATAFORMAT_SUBTYPE_IEEE_FLOAT, "IEEE Float" },
-				{ KSDATAFORMAT_SUBTYPE_MPEG, "MPEG-1" },
-				{ KSDATAFORMAT_SUBTYPE_MULAW, "Mu-law" },
-				{ KSDATAFORMAT_SUBTYPE_PCM, "PCM" },
-				}, [](const GUID& guid) {
-				char str[128];
-				// Shamelessly stolen from https://stackoverflow.com/a/18555932/172594
-				snprintf(str, sizeof(str), "{%08X-%04X-%04X-%02X%02X-%02X%02X%02X%02X%02X%02X}", guid.Data1, guid.Data2, guid.Data3, guid.Data4[0], guid.Data4[1], guid.Data4[2], guid.Data4[3], guid.Data4[4], guid.Data4[5], guid.Data4[6], guid.Data4[7]);
-				return std::string(str);
+	std::string GetWaveFormatChannelMaskString(DWORD channelMask) {
+		return BitfieldToString(channelMask, {
+			{SPEAKER_FRONT_LEFT, "Front Left"},
+			{SPEAKER_FRONT_RIGHT, "Front Right"},
+			{SPEAKER_FRONT_CENTER, "Front Center"},
+			{SPEAKER_LOW_FREQUENCY, "Low Frequency"},
+			{SPEAKER_BACK_LEFT, "Back Left"},
+			{SPEAKER_BACK_RIGHT, "Back Right"},
+			{SPEAKER_FRONT_LEFT_OF_CENTER, "Front Left of Center"},
+			{SPEAKER_FRONT_RIGHT_OF_CENTER, "Front Right of Center"},
+			{SPEAKER_BACK_CENTER, "Back Center"},
+			{SPEAKER_SIDE_LEFT, "Side Left"},
+			{SPEAKER_SIDE_RIGHT, "Side Right"},
+			{SPEAKER_TOP_CENTER, "Top Center"},
+			{SPEAKER_TOP_FRONT_LEFT, "Top Front Left"},
+			{SPEAKER_TOP_FRONT_CENTER, "Top Front Center"},
+			{SPEAKER_TOP_FRONT_RIGHT, "Top Front Right"},
+			{SPEAKER_TOP_BACK_LEFT, "Top Back Left"},
+			{SPEAKER_TOP_BACK_CENTER, "Top Back Center"},
+			{SPEAKER_TOP_BACK_RIGHT, "Top Back Right"},
 			});
-		}
+	}
 
+	std::string GetWaveSubFormatString(const GUID& subFormat) {
+		return EnumToString(subFormat, {
+			{ KSDATAFORMAT_SUBTYPE_ADPCM, "ADPCM" },
+			{ KSDATAFORMAT_SUBTYPE_ALAW, "A-law" },
+			{ KSDATAFORMAT_SUBTYPE_DRM, "DRM" },
+			{ KSDATAFORMAT_SUBTYPE_IEC61937_DOLBY_DIGITAL_PLUS, "IEC61937 Dolby Digital Plus" },
+			{ KSDATAFORMAT_SUBTYPE_IEC61937_DOLBY_DIGITAL, "IEC61937 Dolby Digital" },
+			{ KSDATAFORMAT_SUBTYPE_IEEE_FLOAT, "IEEE Float" },
+			{ KSDATAFORMAT_SUBTYPE_MPEG, "MPEG-1" },
+			{ KSDATAFORMAT_SUBTYPE_MULAW, "Mu-law" },
+			{ KSDATAFORMAT_SUBTYPE_PCM, "PCM" },
+			}, [](const GUID& guid) {
+			char str[128];
+			// Shamelessly stolen from https://stackoverflow.com/a/18555932/172594
+			snprintf(str, sizeof(str), "{%08X-%04X-%04X-%02X%02X-%02X%02X%02X%02X%02X%02X}", guid.Data1, guid.Data2, guid.Data3, guid.Data4[0], guid.Data4[1], guid.Data4[2], guid.Data4[3], guid.Data4[4], guid.Data4[5], guid.Data4[6], guid.Data4[7]);
+			return std::string(str);
+		});
 	}
 
 	std::string DescribeWaveFormat(const WAVEFORMATEXTENSIBLE& waveFormatExtensible) {

FlexASIOUtil/portaudio.h

@@ -51,6 +51,9 @@ namespace flexasio {
 
 	WAVEFORMATEXTENSIBLE GetWasapiDeviceDefaultFormat(PaDeviceIndex index);
 
+	std::string GetWaveFormatTagString(WORD formatTag);
+	std::string GetWaveFormatChannelMaskString(DWORD channelMask);
+	std::string GetWaveSubFormatString(const GUID& subFormat);
 	std::string DescribeWaveFormat(const WAVEFORMATEXTENSIBLE& waveFormatExtensible);
 
 	std::string DescribeStreamParameters(const PaStreamParameters& parameters);