Remove dependency of AudioIO on Scrubbing.cpp ...

... though the demotion of the constant into AudioIO.h isn't wholly satisfactory
and there is still the scrubbing queue in AudioIO

src/AudioIO.cpp

@@ -518,8 +518,6 @@ constexpr size_t TimeQueueGrainSize = 2000;
 
 #ifdef EXPERIMENTAL_SCRUBBING_SUPPORT
 
-#include "tracks/ui/Scrubbing.h"
-
 #ifdef __WXGTK__
    // Might #define this for a useful thing on Linux
    #undef REALTIME_ALSA_THREAD
@@ -1704,17 +1702,11 @@ int AudioIO::StartStream(const TransportTracks &tracks,
    mAudioThreadShouldCallFillBuffersOnce = true;
 
    while( mAudioThreadShouldCallFillBuffersOnce ) {
-#ifndef USE_SCRUB_THREAD
-      // Yuck, we either have to poll "by hand" when scrub polling doesn't
-      // work with a thread, or else yield to timer messages, but that would
-      // execute too much else
-      if (mScrubState) {
-         Scrubber::Get( *mOwningProject ).ContinueScrubbingPoll();
-         wxMilliSleep( Scrubber::ScrubPollInterval_ms * 0.9 );
+      auto interval = 50ull;
+      if (options.playbackStreamPrimer) {
+         interval = options.playbackStreamPrimer();
       }
-      else
-#endif
-        wxMilliSleep( 50 );
+      wxMilliSleep( interval );
    }
 
    if(mNumPlaybackChannels > 0 || mNumCaptureChannels > 0) {
@@ -2544,7 +2536,7 @@ AudioThread::ExitCode AudioThread::Entry()
    {
       using Clock = std::chrono::steady_clock;
       auto loopPassStart = Clock::now();
-      const auto interval = Scrubber::ScrubPollInterval_ms;
+      const auto interval = ScrubPollInterval_ms;
 
       // Set LoopActive outside the tests to avoid race condition
       gAudioIO->mAudioThreadFillBuffersLoopActive = true;

src/AudioIO.h

@@ -789,4 +789,6 @@ private:
    void StartStreamCleanup(bool bOnlyBuffers = false);
 };
 
+static constexpr unsigned ScrubPollInterval_ms = 50;
+
 #endif

src/AudioIOBase.h

@@ -16,6 +16,7 @@ Paul Licameli split from AudioIO.h
 
 #include <atomic>
 #include <cfloat>
+#include <functional>
 #include <memory>
 #include <vector>
 #include <wx/string.h>
@@ -102,6 +103,11 @@ struct AudioIOStartStreamOptions
 
    // contents may get swapped with empty vector
    PRCrossfadeData      *pCrossfadeData{};
+
+   // An unfortunate thing needed just to make scrubbing work on Linux when
+   // we can't use a separate polling thread.
+   // The return value is a number of milliseconds to sleep before calling again
+   std::function< unsigned long() > playbackStreamPrimer;
 };
 
 ///\brief A singleton object supporting queries of the state of any active

src/tracks/ui/Scrubbing.cpp

@@ -56,8 +56,6 @@ enum {
    ScrubSpeedStepsPerOctave = 4,
 #endif
 
-   ScrubPollInterval_ms = 50,
-
    kOneSecondCountdown = 1000 / ScrubPollInterval_ms,
 };
 
@@ -386,6 +384,16 @@ bool Scrubber::MaybeStartScrubbing(wxCoord xx)
             mSpeedPlaying = false;
             auto options =
                DefaultPlayOptions( *mProject );
+
+#ifndef USE_SCRUB_THREAD
+            // Yuck, we either have to poll "by hand" when scrub polling doesn't
+            // work with a thread, or else yield to timer messages, but that would
+            // execute too much else
+            options.playbackStreamPrimer = [this](){
+               ContinueScrubbingPoll();
+               return ScrubPollInterval_ms;
+            };
+#endif
             options.pScrubbingOptions = &mOptions;
             options.envelope = nullptr;
             mOptions.delay = (ScrubPollInterval_ms / 1000.0);
@@ -487,6 +495,17 @@ bool Scrubber::StartSpeedPlay(double speed, double time0, double time1)
    mDragging = false;
 
    auto options = DefaultSpeedPlayOptions( *mProject );
+
+#ifndef USE_SCRUB_THREAD
+            // Yuck, we either have to poll "by hand" when scrub polling doesn't
+            // work with a thread, or else yield to timer messages, but that would
+            // execute too much else
+            options.playbackStreamPrimer = [this](){
+               ContinueScrubbingPoll();
+               return ScrubPollInterval_ms;
+            };
+#endif
+
    options.pScrubbingOptions = &mOptions;
    options.envelope = nullptr;
    mOptions.delay = (ScrubPollInterval_ms / 1000.0);

src/tracks/ui/Scrubbing.h

@@ -40,9 +40,7 @@ class Scrubber final
    : public wxEvtHandler
    , public ClientData::Base
 {
-public:
-   static constexpr unsigned ScrubPollInterval_ms = 50;
-   
+public:   
    static Scrubber &Get( AudacityProject &project );
    static const Scrubber &Get( const AudacityProject &project );