From: FX (
Date: Thu Dec 15 2016 - 05:05:59 CST

Dear John,

> This display issue is probably an issue related to MacOS X Cocoa window
> handling since both FLTK and Tk are linked to Cocoa and Apple's design for
> Cocoa is not really organized to allow sharing of windowing system operations
> among GUI toolkits. I had worked with the FLTK developers to get things
> working in a very basic manner with a previous rev of Tk, but it is quite
> possible that the latest Tk that Sierra is shipping with may have new
> challenges that need to be resolved here.

I am trying to debug the issue, but it is not trivial. As far as I can see, VMDupdate is called when it should be, and in turn it calls “scene->draw” and “scene->draw_finished”. At the end of the line, FltkOpenGLDisplayDevice::update is also being called.

Another information I have gathered is that, even though the on-screen window is not updated correctly (unless I resize it), if I choose “Render” -> “Snapshot”, the generated snapshot is correct (even though the graphics displayed on the screen is not).

I’m willing to invest time and chase this one, but I am a bit at a loss where to go next.