From 84ecb32c98be5f2df04e2c386fb1d0bb0f6d01d0 Mon Sep 17 00:00:00 2001
From: Matthias Melcher <github@matthiasm.com>
Date: Tue, 30 Jan 2024 15:51:37 +0100
Subject: [PATCH] Fix OpenGL context caching on macOS (#737)

---
 FL/mac.H             |  1 +
 src/Fl_Gl_Choice.cxx | 10 ++++++++++
 src/Fl_cocoa.mm      |  5 +++++
 3 files changed, 16 insertions(+)

diff --git a/FL/mac.H b/FL/mac.H
index 8c4e3b994..6d7a51293 100644
--- a/FL/mac.H
+++ b/FL/mac.H
@@ -214,6 +214,7 @@ public:
   static void GLcontext_flushbuffer(NSOpenGLContext*);
   static void GLcontext_release(NSOpenGLContext*);
   static void GLcontext_makecurrent(NSOpenGLContext*);
+  static NSOpenGLContext* GLcontext_getcurrent();
   static void GL_cleardrawable(void);
   static void gl_start(NSOpenGLContext*);
   void destroy(void);
diff --git a/src/Fl_Gl_Choice.cxx b/src/Fl_Gl_Choice.cxx
index fffeda387..071a1a790 100644
--- a/src/Fl_Gl_Choice.cxx
+++ b/src/Fl_Gl_Choice.cxx
@@ -409,6 +409,11 @@ static GLContext cached_context;
 static Fl_Window* cached_window;
 
 void fl_set_gl_context(Fl_Window* w, GLContext context) {
+#ifdef __APPLE_QUARTZ__
+  // macOS may switch buffers during swapping, so we override the
+  // cached context with the actual current context (#737)
+  cached_context = Fl_X::GLcontext_getcurrent();
+#endif
   if (context != cached_context || w != cached_window) {
     cached_context = context;
     cached_window = w;
@@ -439,6 +444,11 @@ void fl_no_gl_context() {
 }
 
 void fl_delete_gl_context(GLContext context) {
+#ifdef __APPLE_QUARTZ__
+  // macOS may switch buffers during swapping, so we override the
+  // cached context with the actual current context (#737)
+  cached_context = Fl_X::GLcontext_getcurrent();
+#endif
   if (cached_context == context) fl_no_gl_context();
 #  if defined(USE_X11)
   glXDestroyContext(fl_display, context);
diff --git a/src/Fl_cocoa.mm b/src/Fl_cocoa.mm
index 630412125..2b8a3dab1 100644
--- a/src/Fl_cocoa.mm
+++ b/src/Fl_cocoa.mm
@@ -3094,6 +3094,11 @@ void Fl_X::GLcontext_makecurrent(NSOpenGLContext* ctxt)
   [ctxt makeCurrentContext];
 }
 
+NSOpenGLContext* Fl_X::GLcontext_getcurrent()
+{
+  return [NSOpenGLContext currentContext];
+}
+
 void Fl_Window::fullscreen_x() {
   _set_fullscreen();
   if (fl_mac_os_version < 101000) {