output/Filtered: add methods SupportsEnableDisable(), SupportsPause()

src/output/Control.cxx

@@ -20,7 +20,6 @@
 #include "config.h"
 #include "Control.hxx"
 #include "Filtered.hxx"
-#include "OutputPlugin.hxx"
 #include "Domain.hxx"
 #include "mixer/MixerControl.hxx"
 #include "notify.hxx"
@@ -127,7 +126,7 @@ void
 AudioOutputControl::EnableAsync()
 {
 	if (!thread.IsDefined()) {
-		if (output->plugin.enable == nullptr) {
+		if (!output->SupportsEnableDisable()) {
 			/* don't bother to start the thread now if the
 			   device doesn't even have a enable() method;
 			   just assign the variable and we're done */
@@ -145,7 +144,7 @@ void
 AudioOutputControl::DisableAsync() noexcept
 {
 	if (!thread.IsDefined()) {
-		if (output->plugin.disable == nullptr)
+		if (!output->SupportsEnableDisable())
 			really_enabled = false;
 		else
 			/* if there's no thread yet, the device cannot
@@ -275,7 +274,7 @@ AudioOutputControl::LockPlay() noexcept
 void
 AudioOutputControl::LockPauseAsync() noexcept
 {
-	if (output->mixer != nullptr && output->plugin.pause == nullptr)
+	if (output->mixer != nullptr && !output->SupportsPause())
 		/* the device has no pause mode: close the mixer,
 		   unless its "global" flag is set (checked by
 		   mixer_auto_close()) */

src/output/Filtered.cxx

@@ -28,6 +28,20 @@
 #include "util/RuntimeError.hxx"
 #include "util/StringBuffer.hxx"
 
+bool
+FilteredAudioOutput::SupportsEnableDisable() const noexcept
+{
+	assert((plugin.enable == nullptr) == (plugin.disable == nullptr));
+
+	return plugin.enable != nullptr;
+}
+
+bool
+FilteredAudioOutput::SupportsPause() const noexcept
+{
+	return plugin.pause != nullptr;
+}
+
 void
 FilteredAudioOutput::Enable()
 {

src/output/Filtered.hxx

@@ -146,6 +146,18 @@ public:
 	}
 
 	/**
+	 * Does the plugin support enabling/disabling a device?
+	 */
+	gcc_pure
+	bool SupportsEnableDisable() const noexcept;
+
+	/**
+	 * Does the plugin support pausing a device?
+	 */
+	gcc_pure
+	bool SupportsPause() const noexcept;
+
+	/**
 	 * Throws #std::runtime_error on error.
 	 */
 	void Enable();