From c31eb6d664ad26940d56f1d9da1778dd9729a187 Mon Sep 17 00:00:00 2001
From: Carl Hetherington <cth@carlh.net>
Date: Sat, 16 Jan 2021 00:55:29 +0100
Subject: [PATCH] Fix OpenGL crashes on macOS (#1899).

---
 src/wx/gl_video_view.cc | 33 ++++++++++++++++++++++++++++++---
 src/wx/gl_video_view.h  |  1 +
 2 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/src/wx/gl_video_view.cc b/src/wx/gl_video_view.cc
index 969264c27..5d40050de 100644
--- a/src/wx/gl_video_view.cc
+++ b/src/wx/gl_video_view.cc
@@ -68,6 +68,7 @@ check_gl_error (char const * last)
 
 GLVideoView::GLVideoView (FilmViewer* viewer, wxWindow *parent)
 	: VideoView (viewer)
+	, _context (nullptr)
 	, _have_storage (false)
 	, _vsync_enabled (false)
 	, _playing (false)
@@ -117,6 +118,11 @@ GLVideoView::update ()
 		if (!_canvas->IsShownOnScreen()) {
 			return;
 		}
+
+#ifdef DCPOMATIC_OSX
+		/* macOS gives errors if we don't do this (and therefore [NSOpenGLContext setView:]) from the main thread */
+		ensure_context ();
+#endif
 	}
 
 	if (!_thread.joinable()) {
@@ -126,6 +132,16 @@ GLVideoView::update ()
 	request_one_shot ();
 }
 
+
+void
+GLVideoView::ensure_context ()
+{
+	if (!_context) {
+		_context = new wxGLContext (_canvas);
+		_canvas->SetCurrent (*_context);
+	}
+}
+
 void
 GLVideoView::draw (Position<int> inter_position, dcp::Size inter_size)
 {
@@ -338,10 +354,21 @@ try
 {
 	{
 		boost::mutex::scoped_lock lm (_canvas_mutex);
-		_context = new wxGLContext (_canvas);
-		_canvas->SetCurrent (*_context);
-	}
 
+#if defined(DCPOMATIC_OSX)
+		/* Without this we see errors like
+		 * ../src/osx/cocoa/glcanvas.mm(194): assert ""context"" failed in SwapBuffers(): should have current context [in thread 700006970000]
+		 */
+		WXGLSetCurrentContext (_context->GetWXGLContext());
+#else
+		/* We must call this here on Linux otherwise we get no image (for reasons
+		 * that aren't clear).  However, doing ensure_context() from this thread
+		 * on macOS gives
+		 * "[NSOpenGLContext setView:] must be called from the main thread".
+		 */
+		ensure_context ();
+#endif
+	}
 
 #if defined(DCPOMATIC_LINUX) && defined(DCPOMATIC_HAVE_GLX_SWAP_INTERVAL_EXT)
 	if (_canvas->IsExtensionSupported("GLX_EXT_swap_control")) {
diff --git a/src/wx/gl_video_view.h b/src/wx/gl_video_view.h
index d8ee65da6..1e6886f26 100644
--- a/src/wx/gl_video_view.h
+++ b/src/wx/gl_video_view.h
@@ -61,6 +61,7 @@ private:
 	void thread_playing ();
 	void request_one_shot ();
 	void check_for_butler_errors ();
+	void ensure_context ();
 
 	/* Mutex for use of _canvas; it's only contended when our ::thread
 	   is started up so this may be overkill.
-- 
2.30.2