Provide workaround for xftfont rendering problem

* src/xftfont.c (syms_of_xftfont) <xft-font-ascent-descent-override>:
New variable.
(xftfont_open): Use it to work around problems with rendering some
fonts.  (Bug#23360)

1 files changed, 24 insertions, 0 deletions

diff --git a/src/xftfont.c b/src/xftfont.c
index 7926325419c..34c6f7d3e42 100644
--- a/src/xftfont.c
+++ b/src/xftfont.c
@@ -395,6 +395,24 @@ xftfont_open (struct frame *f, Lisp_Object entity, int pixel_size)
 
   font->ascent = xftfont->ascent;
   font->descent = xftfont->descent;
+  /* The following workaround is unnecessary on most systems, and
+     causes annoying differences in glyph height between regular and
+     bold fonts (see bug#22383).  However, with some fonts, such as
+     monaco, removing the workaround results in overlapping vertical
+     space of a line, see bug#23360.  As long as the way to reconcile
+     these opposites is not known, we provide a user option to work
+     around the problem.  */
+  if (pixel_size >= 5
+      && xft_font_ascent_descent_override)
+    {
+      /* The above condition is a dirty workaround because
+         XftTextExtents8 behaves strangely for some fonts
+         (e.g. "Dejavu Sans Mono") when pixel_size is less than 5. */
+      if (font->ascent < extents.y)
+        font->ascent = extents.y;
+      if (font->descent < extents.height - extents.y)
+        font->descent = extents.height - extents.y;
+    }
   font->height = font->ascent + font->descent;
 
   if (XINT (AREF (entity, FONT_SIZE_INDEX)) == 0)
@@ -733,6 +751,12 @@ syms_of_xftfont (void)
   DEFSYM (QCembolden, ":embolden");
   DEFSYM (QClcdfilter, ":lcdfilter");
 
+  DEFVAR_BOOL ("xft-font-ascent-descent-override",
+               xft_font_ascent_descent_override,
+               doc:  /* Non-nil means override the ascent and descent values for Xft font driver.
+This is needed with some fonts to correct vertical overlap of glyphs.  */);
+  xft_font_ascent_descent_override = 0;
+
   ascii_printable[0] = 0;
 
   xftfont_driver = ftfont_driver;