6 files changed, 81 insertions, 14 deletions

diff --git a/src/dispextern.h b/src/dispextern.h
index d9d4d2300fa..1537d44330d 100644
--- a/src/dispextern.h
+++ b/src/dispextern.h
@@ -1526,6 +1526,12 @@ struct glyph_string
       + (FRAME_LINE_HEIGHT ((F)) > FONT_HEIGHT ((FONT)))) / 2   \
    - (FONT_DESCENT (FRAME_FONT (F)) - FRAME_BASELINE_OFFSET (F)))
 
+/* A heuristic test for fonts that claim they need a preposterously
+   large vertical space.  The heuristics is in the factor of 3.  We
+   ignore the ascent and descent values reported by such fonts, and
+   instead go by the values reported for individual glyphs.  */
+#define FONT_TOO_HIGH(ft)  ((ft)->ascent + (ft)->descent > 3*(ft)->pixel_size)
+
 
 /***********************************************************************
                                 Faces
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);
     }
diff --git a/src/w32term.c b/src/w32term.c
index 0bc2e980214..9c4f28fa2d4 100644
--- a/src/w32term.c
+++ b/src/w32term.c
@@ -1218,7 +1218,12 @@ x_draw_glyph_string_background (struct glyph_string *s, bool force_p)
         }
       else
 #endif
-        if (FONT_HEIGHT (s->font) < s->height - 2 * box_line_width
+           if (FONT_HEIGHT (s->font) < s->height - 2 * box_line_width
+               /* When xdisp.c ignores FONT_HEIGHT, we cannot trust
+                  font dimensions, since the actual glyphs might be
+                  much smaller.  So in that case we always clear the
+                  rectangle with background color.  */
+               || FONT_TOO_HIGH (s->font)
                || s->font_not_found_p
                || s->extends_to_end_of_line_p
                || force_p)
diff --git a/src/xdisp.c b/src/xdisp.c
index a1b7cf1438f..ed430a424a1 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -25296,12 +25296,6 @@ draw_glyphs (struct window *w, int x, struct glyph_row *row,
       }                                                 \
   }
 
-/* A heuristic test for fonts that claim they need a preposterously
-   large vertical space.  The heuristics is in the factor of 3.  We
-   ignore the ascent and descent values reported by such fonts, and
-   instead go by the values reported for individual glyphs.  */
-#define FONT_TOO_HIGH(ft)  ((ft)->ascent + (ft)->descent > 3*(ft)->pixel_size)
-
 /* Store one glyph for IT->char_to_display in IT->glyph_row.
    Called from x_produce_glyphs when IT->glyph_row is non-null.  */
 
@@ -26230,8 +26224,28 @@ produce_glyphless_glyph (struct it *it, bool for_no_font, Lisp_Object acronym)
      ASCII face.  */
   face = FACE_FROM_ID (it->f, it->face_id)->ascii_face;
   font = face->font ? face->font : FRAME_FONT (it->f);
-  it->ascent = FONT_BASE (font) + font->baseline_offset;
-  it->descent = FONT_DESCENT (font) - font->baseline_offset;
+  it->ascent = FONT_BASE (font);
+  it->descent = FONT_DESCENT (font);
+  /* Attempt to fix box height for fonts that claim preposterously
+     large height.  */
+  if (FONT_TOO_HIGH (font))
+    {
+      XChar2b char2b;
+
+      /* Get metrics of a reasonably sized ASCII character.  */
+      if (get_char_glyph_code ('{', font, &char2b))
+        {
+          struct font_metrics *pcm = get_per_char_metric (font, &char2b);
+
+          if (!(pcm->width == 0 && pcm->rbearing == 0 && pcm->lbearing == 0))
+            {
+              it->ascent = pcm->ascent;
+              it->descent = pcm->descent;
+            }
+        }
+    }
+  it->ascent += font->baseline_offset;
+  it->descent -= font->baseline_offset;
   base_height = it->ascent + it->descent;
   base_width = font->average_width;
 
diff --git a/src/xftfont.c b/src/xftfont.c
index 0e8b876f1d3..a1846e8d461 100644
--- a/src/xftfont.c
+++ b/src/xftfont.c
@@ -617,8 +617,26 @@ xftfont_draw (struct glyph_string *s, int from, int to, int x, int y,
     XftDrawSetClip (xft_draw, NULL);
 
   if (with_background)
-    XftDrawRect (xft_draw, &bg,
-                 x, y - s->font->ascent, s->width, s->font->height);
+    {
+      int height = FONT_HEIGHT (s->font), ascent = FONT_BASE (s->font);
+
+      /* Font's global height and ascent 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))
+        height = ascent =
+          s->first_glyph->slice.glyphless.lower_yoff
+          - s->first_glyph->slice.glyphless.upper_yoff;
+      XftDrawRect (xft_draw, &bg, x, y - ascent, s->width, height);
+    }
   code = alloca (sizeof (FT_UInt) * len);
   for (i = 0; i < len; i++)
     code[i] = ((XCHAR2B_BYTE1 (s->char2b + from + i) << 8)
diff --git a/src/xterm.c b/src/xterm.c
index 4f5dfed9ae8..58563ff35d0 100644
--- a/src/xterm.c
+++ b/src/xterm.c
@@ -1724,6 +1724,11 @@ x_draw_glyph_string_background (struct glyph_string *s, bool force_p)
           s->background_filled_p = true;
         }
       else if (FONT_HEIGHT (s->font) < s->height - 2 * box_line_width
+               /* When xdisp.c ignores FONT_HEIGHT, we cannot trust
+                  font dimensions, since the actual glyphs might be
+                  much smaller.  So in that case we always clear the
+                  rectangle with background color.  */
+               || FONT_TOO_HIGH (s->font)
                || s->font_not_found_p
                || s->extends_to_end_of_line_p
                || force_p)