I have been writing my FLTK application with the 1.4.x branch since I switched to Mac OSX Mojave platform for development. I am currently writing custom drawing code inside a Fl_Cairo_Window subclass. What the drawing code does is call widget->redraw() on all of the child widgets, then a call to Fl_Double_Window::draw(), then draws some diagrams with the current cairo context (set with the set_draw_cb method), and then finally does some additional small drawing operations onto the window using the fl_draw.H methods. This works well on my Linux box for 1.3.x and 1.4.x, but when I log into the new Mojave box, this window gets displayed as flipped. I have read up on this 2D Quartz flipping of the coordinate system in the FLTK docs. Strangely enough the widgets are drawn correctly the first time they are placed. When my custom draw functions are called, however, the buffer gets "reflipped" somehow and is drawn upside down and reflected across the screen. 

I can post more specific code snippets if you need them for debugging, but my code is a little long and this pretty much describes what's going on in my draw routines. Is it possible that this weirdness is something new and Mojave-specific? I couldn't get FLTK to display the windowing correctly with 1.3.x on Mojave. Is there some other option I need to be setting to keep the screen from flipping? 

Thanks.