Fix cross macOS version building (bug#28222)

* src/macfont.h (CGContextSetFontSmoothingStyle): Function
declaration.
* src/macfont.m (macfont_draw): Limit new code to macOS 10.8 and up.

2 files changed, 11 insertions, 1 deletions

diff --git a/src/macfont.h b/src/macfont.h
index 32899908be9..3a66d2d005a 100644
--- a/src/macfont.h
+++ b/src/macfont.h
@@ -82,3 +82,10 @@ typedef const struct _EmacsScreenFont *ScreenFontRef; /* opaque */
 extern void mac_register_font_driver (struct frame *f);
 extern void *macfont_get_nsctfont (struct font *font);
 extern void macfont_update_antialias_threshold (void);
+
+#if MAC_OS_X_VERSION_MAX_ALLOWED >= 1080
+/* This is an undocumented function that is probably not available
+   pre-10.8. */
+extern void CGContextSetFontSmoothingStyle(CGContextRef, int)
+  __attribute__((weak_import));
+#endif
diff --git a/src/macfont.m b/src/macfont.m
index 59891353cd3..33c28f7349a 100644
--- a/src/macfont.m
+++ b/src/macfont.m
@@ -2888,11 +2888,14 @@ macfont_draw (struct glyph_string *s, int from, int to, int x, int y,
       if (no_antialias_p)
         CGContextSetShouldAntialias (context, false);
 
-      if (!NILP (ns_use_thin_smoothing))
+#if MAC_OS_X_VERSION_MAX_ALLOWED >= 1080
+      if (!NILP (ns_use_thin_smoothing)
+          && CGContextSetFontSmoothingStyle != NULL)
         {
           CGContextSetShouldSmoothFonts(context, YES);
           CGContextSetFontSmoothingStyle(context, 16);
         }
+#endif
 
       CGContextSetTextMatrix (context, atfm);
       CGContextSetTextPosition (context, text_position.x, text_position.y);