Fix display of glyphless characters with problematic fonts

* src/w32term.c (x_draw_glyph_string_background): Force redraw of
glyph string background also when the font in use claims
preposterously large global height value.  Helps to remove
artifacts left from previous displays when glyphless characters
are displayed as hex code in a box.
* src/xterm.c (x_draw_glyph_string_background): Force redraw of
glyph string background also when the font in use claims
preposterously large global height value.  Helps to remove
artifacts left from previous displays when glyphless characters
are displayed as hex code in a box.
* src/w32font.c (w32font_draw): Fix background drawing for
glyphless characters that display as acronyms or hex codes in a
box.
* src/xftfont.c (xftfont_draw): Fix background drawing for
glyphless characters that display as acronyms or hex codes in a
box.
* src/xdisp.c (produce_glyphless_glyph): Compute reasonable values
for it->ascent and it->descent when the font claims preposterously
large global values.
(FONT_TOO_HIGH): Move from here...
* src/dispextern.h (FONT_TOO_HIGH): ...to here.

1 files changed, 22 insertions, 3 deletions

diff --git a/src/w32font.c b/src/w32font.c
index 6306a8460e7..1c2f9665037 100644
--- a/src/w32font.c
+++ b/src/w32font.c
@@ -650,12 +650,31 @@ w32font_draw (struct glyph_string *s, int from, int to,
       HBRUSH brush;
       RECT rect;
       struct font *font = s->font;
-
+      int ascent = font->ascent, descent = font->descent;
+
+      /* Font's global ascent and descent values might be
+	 preposterously large for some fonts.  We fix here the case
+	 when those fonts are used for display of glyphless
+	 characters, because drawing background with font dimensions
+	 in those cases makes the display illegible.  There's only one
+	 more call to the draw method with with_background set to
+	 true, and that's in x_draw_glyph_string_foreground, when
+	 drawing the cursor, where we have no such heuristics
+	 available.  FIXME.  */
+      if (s->first_glyph->type == GLYPHLESS_GLYPH
+	  && (s->first_glyph->u.glyphless.method == GLYPHLESS_DISPLAY_HEX_CODE
+	      || s->first_glyph->u.glyphless.method == GLYPHLESS_DISPLAY_ACRONYM))
+	{
+	  ascent =
+	    s->first_glyph->slice.glyphless.lower_yoff
+	    - s->first_glyph->slice.glyphless.upper_yoff;
+	  descent = 0;
+	}
       brush = CreateSolidBrush (s->gc->background);
       rect.left = x;
-      rect.top = y - font->ascent;
+      rect.top = y - ascent;
       rect.right = x + s->width;
-      rect.bottom = y + font->descent;
+      rect.bottom = y + descent;
       FillRect (s->hdc, &rect, brush);
       DeleteObject (brush);
     }