Changing pixel density in GL test app makes map go blank

[danpat]

I just built make run-osx from 9d6cb13 to test some map rendering using GL-native on OSX.

I have a MBP 13" with a Retina display, and an external Dell monitor running at 2560x1440 (non-retina):

If I drag the Mapbox GL app from the retina display to the non-retina display, the map goes blank, and won't come back unless I restart the app. Interaction seems to still work and all the controls are still there:

Launched on the non-retina display:

Launched on the retina display:

Moved from Retina to non-Retina:

In addition, the following warning is printed to the console when I move between from the launch pixel density to a different pixel density:

2016-01-06 09:43:16.702 Mapbox GL[27089:22073075] Unable to simultaneously satisfy constraints:
(
    "<NSLayoutConstraint:0x7fe02bf99190 NSSlider:0x7fe02bc6d3e0.centerX == NSSegmentedControl:0x7fe02bc82b40.centerX>",
    "<NSLayoutConstraint:0x7fe02bca1ba0 NSSlider:0x7fe02bc6d3e0.centerX == NSSegmentedControl:0x7fe02bc82b40.centerX>"
)

Will attempt to recover by breaking constraint
<NSLayoutConstraint:0x7fe02bf99190 NSSlider:0x7fe02bc6d3e0.centerX == NSSegmentedControl:0x7fe02bc82b40.centerX>

Set the NSUserDefault NSConstraintBasedLayoutVisualizeMutuallyExclusiveConstraints to YES to have -[NSWindow visualizeConstraints:] automatically called when this happens.  And/or, break on objc_exception_throw to catch this in the debugger.

[danpat]

Note: the "Launched on non-retina display" image also seems to have poor antialiasing on the edges of lines and fonts.

[jfirebaugh]

⇢ #6654