…operties from a non-main thread

This issue presents when rendering from a thread that is other than the window thread, more easily reproduced when disabling vsync

This commit aims to populate the relevant data into backend_data, by way of dispatch_async (ocurring on the main thread). Those particular backend data items are protected by an NSlock

There may be more elegant ways to do this

Main Thread Checker
imgui/backends/imgui_impl_osx.mm:608 -[NSView window] must be used from main thread only
imgui/backends/imgui_impl_osx.mm:608 -[NSWindow backingScaleFactor] must be used from main thread only
imgui/backends/imgui_impl_osx.mm:609 -[NSView bounds] must be used from main thread only

…operties from a non-main thread

This issue presents when rendering from a thread that is other than the window thread, more easily reproduced when disabling vsync

This commit aims to populate the relevant data into backend_data, by way of dispatch_async (ocurring on the main thread). Those particular backend data items are protected by an NSlock

There may be more elegant ways to do this

Main Thread Checker
imgui/backends/imgui_impl_osx.mm:608 -[NSView window] must be used from main thread only
imgui/backends/imgui_impl_osx.mm:608 -[NSWindow backingScaleFactor] must be used from main thread only
imgui/backends/imgui_impl_osx.mm:609 -[NSView bounds] must be used from main thread only

…anitiser concerns

This is a little nasty..
I'm trying to keep all changes localised to imgui_impl_osx.mm

Ideally the ImGui_IO_lock would live within ImGuiIO but I didn't want to muddy the waters

Perhaps better if this lock primitive is delivered through BackendPlatformUserData, and only used where provided

This change requires the client platform to explicitly lock the primitive from outside of ImGui around ImGui::NewFrame specifically, and additionally from anywhere on the client side (external to ImGui) that concurrently hooks into ImGuiIO

That requires the client to define an extern lock (and use it appropriately)
 extern NSlock *ImGui_IO_lock

If this lock were native to ImGui we could have ImGui::NewFrame() handle the lock on our behalf, negating the need for client side locking

…oints