Fix Catalina by moving some calls to the UI thread.

RELEASE_NOTES.md

@@ -5,6 +5,7 @@ A new header is inserted each time a *tag* is created.
 
 ## Next release
 
+- Fix bad instruction exception with macOS Catalina.
 - Added support for solid and thin layer cubemap and screen-space refraction.
 - Improved high roughness material rendering by default when regenerating environments maps.
 - Fixed bad state after removing an IBL from the Scene.

filament/backend/src/opengl/PlatformCocoaGL.mm

@@ -108,21 +108,17 @@
     NSView *nsView = (__bridge NSView*) drawSwapChain;
     if (pImpl->mCurrentView != nsView) {
         pImpl->mCurrentView = nsView;
-        // Calling setView could change the viewport and/or scissor box state, but this isn't
-        // accounted for in our OpenGL driver- so we save their state and recall it afterwards.
-        GLint viewport[4];
-        GLint scissor[4];
-        glGetIntegerv(GL_VIEWPORT, viewport);
-        glGetIntegerv(GL_SCISSOR_BOX, scissor);
-
-        [pImpl->mGLContext setView:nsView];
-
-        // Recall viewport and scissor state.
-        glViewport(viewport[0], viewport[1], viewport[2], viewport[3]);
-        glScissor(scissor[0], scissor[1], scissor[2], scissor[3]);
+
+        // NOTE: This is not documented well (if at all) but Apple requires the following two
+        // context methods to be called from the UI thread. This became a hard requirement with the
+        // arrival of macOS 10.15 (Catalina). If we were to call these methods from the GL thread,
+        // we would see EXC_BAD_INSTRUCTION.
+        NSOpenGLContext* glContext = pImpl->mGLContext;
+        dispatch_sync(dispatch_get_main_queue(), ^(void) {
+            [glContext setView:nsView];
+            [glContext update];
+        });
     }
-    // this is needed only when the view resized. Not sure how to do only when needed.
-    [pImpl->mGLContext update];
 }
 
 void PlatformCocoaGL::commit(Platform::SwapChain* swapChain) noexcept {