NSAttributedString: Weird/different font metrics reported by on Big Sur/arm?

I have the following code:

Code Block
var codeFont := NSFont.fontWithName("SF Mono Regular") size(11);
var attributes := new NSMutableDictionary<NSAttributedStringKey,id>();
attributes[NSFontAttributeName] := codeFont;
attributes[NSForegroundColorAttributeName] := NSColor.blackColor;;
var charSize := new NSAttributedString withString("Q") attributes(attributes).size;
writeLn("attributes {0}", attributes);
writeLn("codeFont {0}", codeFont);
writeLn("charSize.height {0}", charSize.height);


on Catalina, it prints

Code Block
attributes {
NSColor = "NSCalibratedWhiteColorSpace 0 1";
NSFont = "\"SFMono-Regular 11.00 pt. P [] (0x14f73aa80) fobj=0x14f728120, spc=6.80\"";
}
codeFont "SFMono-Regular 11.00 pt. P [] (0x14f73aa80) fobj=0x14f728120, spc=6.80"
charSize.height 17


When I build and run it on a Big Sur/Intel machine, it prints the same. When I build and run it on an Big Sur/M1 machine *without a deloyment target set, is also prints the same. but: if I build with a deployment target of 10.15 (*), I suddenly get:

Code Block
attributes {
NSColor = "Generic Gray Gamma 2.2 Profile colorspace 0 1";
NSFont = "\"SFMono-Regular 11.00 pt. P [] (0x142f26dc0) fobj=0x142f1fad0, spc=6.80\"";
}
codeFont "SFMono-Regular 11.00 pt. P [] (0x142f27500) fobj=0x142f1fad0, spc=6.80"
charSize.height 13


Note that the height of the string is reported at 4 display points smaller than it should (also, the font name is shown as "gray" instead of black, but ok...)

If I actually draw, the font draws the same size (and proper black) — but all my metrics that calculate where and what to draw based on what size gives me are of course off, so everything goes wrong (e.g. I end up drawing lines too tight together)

What could going on here? is this "as designed" or am I missing something?





(* actually, it might be a bit more complicated than that. The above is with our own compiler, Elements, and repros consistently, when I switch the deployment target back and forth. Compiling the equivalent ObjC with Xcode 12.2 or 12.3 Beta, I always get the wrong value of 13, even if I drop the deployment target. And to make things more complicated, I have an Intel-only build of my app, migrated from my Catalina/Intel machine, that has the proper behavior even when run on Big Sur/M3, but the same app from our build system, also Catalina, shows the same wrong behavior. it's all very weird)
Reported as Feedback FB8923628
NSAttributedString: Weird/different font metrics reported by on Big Sur/arm?
 
 
Q