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We are developing a graphics app that uses OpenGL extensively. We've developed a crash issue since we switched to CALayer-based OpenGL rendering per Apple sample code CALayerEssentials. When certain of our OpenGL layer-containing windows are moved between two screens, the app crashes (on Catalina). I replicated the issue in a pared-down, updated version of CALayerEssentials. In our version, because we will have multiple OpenGL views sharing resources, we use a shared context. Is there something we can do differently to avoid the crash while still sharing OpenGL resources? // You would typically override this method if you needed to specify a share context to share OpenGL resources. // This is also an ideal location to do any initialization that is necessary for the context returned -(CGLContextObj)copyCGLContextForPixelFormat:(CGLPixelFormatObj)pixelFormat { #if 0 // ORIGINAL SAMPLE CODE // Default handling is fine for this demonstration. CGLContextObj superContext = [super copyCGLContextForPixelFormat:pixelFormat]; return superContext; #else // OUR VERSION TO SHARE OPENGL RESOURCES // THIS LEADS TO CRASH WHEN WINDOW IS MOVED BETWEEN SCREENS if (!_dfContext) { _dfContext = [super copyCGLContextForPixelFormat:pixelFormat]; } return _dfContext; #endif } Our pared-down and updated version of CALayerEssentials source may be downloaded here. Here's the backtrace: Thread 0 Crashed:: Dispatch queue: com.apple.main-thread 0 GLEngine 0x00007fff3eb701a2 gleLookupHashObject + 13 1 GLEngine 0x00007fff3eb6fe3e gleBindTexture + 59 2 GLEngine 0x00007fff3eb6fdc6 glBindTexture_Exec + 405 3 com.apple.QuartzCore 0x00007fff3fbd8a0c CA::(anonymous namespace)::IOSurface::framebuffer() + 84 4 com.apple.QuartzCore 0x00007fff3fbd8907 CA::(anonymous namespace)::IOSurface::attach() + 83 5 com.apple.QuartzCore 0x00007fff3fbd8461 CAOpenGLLayerDraw(CAOpenGLLayer*, double, CVTimeStamp const*, unsigned int) + 1868 6 com.apple.QuartzCore 0x00007fff3fbd7b3a -[CAOpenGLLayer _display] + 580 7 com.apple.QuartzCore 0x00007fff3fb3bcad CA::Layer::display_if_needed(CA::Transaction*) + 757 8 com.apple.QuartzCore 0x00007fff3fb19fca CA::Context::commit_transaction(CA::Transaction*, double) + 334 9 com.apple.QuartzCore 0x00007fff3fb18bb4 CA::Transaction::commit() + 644 10 com.apple.AppKit 0x00007fff315f42f1 __62+[CATransaction(NSCATransaction) NS_setFlushesWithDisplayLink]_block_invoke + 266 11 com.apple.AppKit 0x00007fff31d12c20 ___NSRunLoopObserverCreateWithHandler_block_invoke + 41 12 com.apple.CoreFoundation 0x00007fff341f17bc __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 23 13 com.apple.CoreFoundation 0x00007fff341f16ec __CFRunLoopDoObservers + 457 14 com.apple.CoreFoundation 0x00007fff341f0c84 __CFRunLoopRun + 884 15 com.apple.CoreFoundation 0x00007fff341f02b3 CFRunLoopRunSpecific + 466 16 com.apple.HIToolbox 0x00007fff32e0baad RunCurrentEventLoopInMode + 292

I've recently noticed that use of NSSavePanel in our macOS application causes one or more warnings to the console, like this: WARNING: <NSSavePanel: 0x171a466d0> found it necessary to prepare implicitly; please prepare panels using NSSavePanel rather than NSApplication or NSWindow. WARNING: <NSSavePanel: 0x171a466d0> found it necessary to start implicitly; please start panels using NSSavePanel rather than NSApplication or NSWindow. WARNING: <NSSavePanel: 0x171a466d0> running implicitly; please run panels using NSSavePanel rather than NSApplication. We are running the save panel modally, as supported by NSSavePanel.h: NSSavePanel * panel = [NSSavePanel savePanel]; [panel setTitle:@"Record Movie"]; ... NSModalResponse rtn = [panel runModal]; In other code, we use RunModalSheetForDialog() which gives a similar warning: <NSSavePanel: 0x7f9c70224810> running implicitly; please run panels using NSSavePanel rather than NSApplication. Why these warnings, and what can I do about it?