update engine to allow latency measurement w/o restart.

diff --git a/libs/ardour/audioengine.cc b/libs/ardour/audioengine.cc
index 5bd2d4dce4cb8e3c71dfec5f6f9ddc5426c03b2d..a87a5ee7d0192015a07e17c34a812d6acd255f20 100644 (file)
--- a/libs/ardour/audioengine.cc
+++ b/libs/ardour/audioengine.cc
@@ -867,6 +867,8 @@ AudioEngine::start (bool for_latency)
 int
 AudioEngine::stop (bool for_latency)
 {
+       bool stop_engine = true;
+
        if (!_backend) {
                return 0;
        }
@@ -877,15 +879,20 @@ AudioEngine::stop (bool for_latency)
                pl.acquire ();
        }
 
-       if (_backend->stop ()) {
-               return -1;
+       if (for_latency && _backend->can_change_systemic_latency_when_running()) {
+               stop_engine = false;
+       } else {
+               if (_backend->stop ()) {
+                       pl.release ();
+                       return -1;
+               }
        }
 
        if (pl.locked ()) {
                pl.release ();
        }
 
-       if (_session && _running &&
+       if (_session && _running && stop_engine &&
            (_session->state_of_the_state() & Session::Loading) == 0 &&
            (_session->state_of_the_state() & Session::Deletion) == 0) {
                // it's not a halt, but should be handled the same way:
@@ -893,16 +900,20 @@ AudioEngine::stop (bool for_latency)
                _session->engine_halted ();
        }
 
-       _running = false;
+       if (stop_engine) {
+               _running = false;
+       }
        _processed_frames = 0;
        _measuring_latency = MeasureNone;
        _latency_output_port = 0;
        _latency_input_port = 0;
        _started_for_latency = false;
 
-       Port::PortDrop ();
+       if (stop_engine) {
+               Port::PortDrop ();
+       }
 
-       if (!for_latency) {
+       if (!for_latency && stop_engine) {
                Stopped (); /* EMIT SIGNAL */
        }
 
@@ -1272,6 +1283,19 @@ AudioEngine::setup_required () const
 int
 AudioEngine::prepare_for_latency_measurement ()
 {
+       if (!_backend) {
+               return -1;
+       }
+
+       if (_backend->can_change_systemic_latency_when_running()) {
+               if (start()) {
+                       return -1;
+               }
+               _backend->set_systemic_input_latency (0);
+               _backend->set_systemic_output_latency (0);
+               return 0;
+       }
+
        if (running()) {
                _stopped_for_latency = true;
                stop (true);
@@ -1288,10 +1312,8 @@ AudioEngine::prepare_for_latency_measurement ()
 int
 AudioEngine::start_latency_detection (bool for_midi)
 {
-       if (!running()) {
-               if (prepare_for_latency_measurement ()) {
-                       return -1;
-               }
+       if (prepare_for_latency_measurement ()) {
+               return -1;
        }
 
        PortEngine& pe (port_engine());
@@ -1398,7 +1420,9 @@ AudioEngine::stop_latency_detection ()
                _latency_input_port = 0;
        }
 
-       stop (true);
+       if (!_backend->can_change_systemic_latency_when_running()) {
+               stop (true);
+       }
 
        if (_stopped_for_latency) {
                start ();