From 655b20bae493a517bd2163a1af379fd57abd3457 Mon Sep 17 00:00:00 2001
From: David Robillard <d@drobilla.net>
Date: Tue, 11 May 2021 12:09:17 -0400
Subject: Add Cleared event for implementing refresh without a race

---
 src/Drivers.cpp         | 2 ++
 src/Event.hpp           | 5 ++++-
 src/Patchage.cpp        | 2 +-
 src/event_to_string.cpp | 2 ++
 src/handle_event.cpp    | 2 ++
 5 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/src/Drivers.cpp b/src/Drivers.cpp
index 94ab6f9..4f57f34 100644
--- a/src/Drivers.cpp
+++ b/src/Drivers.cpp
@@ -41,6 +41,8 @@ Drivers::Drivers(ILog& log, Driver::EventSink emit_event)
 void
 Drivers::refresh()
 {
+  _emit_event(event::Cleared{});
+
   if (_alsa_driver) {
     _alsa_driver->refresh(_emit_event);
   }
diff --git a/src/Event.hpp b/src/Event.hpp
index 378f35eb..233d1a1 100644
--- a/src/Event.hpp
+++ b/src/Event.hpp
@@ -28,6 +28,8 @@
 namespace patchage {
 namespace event {
 
+struct Cleared {};
+
 struct ClientCreated {
   ClientID   id;
   ClientInfo info;
@@ -67,7 +69,8 @@ struct PortsDisconnected {
 } // namespace event
 
 /// An event from drivers that represents a change to the system
-using Event = boost::variant<event::ClientCreated,
+using Event = boost::variant<event::Cleared,
+                             event::ClientCreated,
                              event::ClientDestroyed,
                              event::DriverAttached,
                              event::DriverDetached,
diff --git a/src/Patchage.cpp b/src/Patchage.cpp
index 5045691..7387b36 100644
--- a/src/Patchage.cpp
+++ b/src/Patchage.cpp
@@ -473,7 +473,7 @@ Patchage::refresh()
   };
 
   if (_canvas) {
-    _canvas->clear();
+    sink(event::Cleared{});
 
     if (_drivers.jack()) {
       _drivers.jack()->refresh(sink);
diff --git a/src/event_to_string.cpp b/src/event_to_string.cpp
index 4b23875..c8a6c42 100644
--- a/src/event_to_string.cpp
+++ b/src/event_to_string.cpp
@@ -56,6 +56,8 @@ struct EventPrinter {
     PATCHAGE_UNREACHABLE();
   }
 
+  std::string operator()(const event::Cleared&) { return "Cleared"; }
+
   std::string operator()(const event::DriverAttached& event)
   {
     return fmt::format("Attached to {}", (*this)(event.type));
diff --git a/src/handle_event.cpp b/src/handle_event.cpp
index fa11ec3..65f4705 100644
--- a/src/handle_event.cpp
+++ b/src/handle_event.cpp
@@ -48,6 +48,8 @@ public:
     : _patchage{patchage}
   {}
 
+  void operator()(const event::Cleared&) { _patchage.canvas()->clear(); }
+
   void operator()(const event::DriverAttached& event)
   {
     _patchage.driver_attached(event.type);
-- 
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