(Ffont_shape_text): Avoid unnecessary composition.

1 files changed, 26 insertions, 14 deletions

diff --git a/src/font.c b/src/font.c
index 51f9ffa0a24..10dce4764a2 100644
--- a/src/font.c
+++ b/src/font.c
@@ -3581,13 +3581,18 @@ The value is the end position of the shaped text.  */)
       EMACS_INT this_from = LGLYPH_FROM (g);
       EMACS_INT this_to = LGLYPH_TO (g) + 1;
       int j, k;
+      int need_composition = 0;
 
       metrics.lbearing = LGLYPH_LBEARING (g);
       metrics.rbearing = LGLYPH_RBEARING (g);
       metrics.ascent = LGLYPH_ASCENT (g);
       metrics.descent = LGLYPH_DESCENT (g);
       if (NILP (LGLYPH_ADJUSTMENT (g)))
-        metrics.width = LGLYPH_WIDTH (g);
+        {
+          metrics.width = LGLYPH_WIDTH (g);
+          if (XINT (LGLYPH_CHAR (g)) == 0 || metrics.width == 0)
+            need_composition = 1;
+        }
       else
         {
           metrics.width = LGLYPH_WADJUST (g);
@@ -3595,6 +3600,7 @@ The value is the end position of the shaped text.  */)
           metrics.rbearing += LGLYPH_XOFF (g);
           metrics.ascent -= LGLYPH_YOFF (g);
           metrics.descent += LGLYPH_YOFF (g);
+          need_composition = 1;
         }
       for (j = i + 1; j < XINT (n); j++)
         {
@@ -3603,6 +3609,7 @@ The value is the end position of the shaped text.  */)
           g = LGSTRING_GLYPH (gstring, j);
           if (this_from != LGLYPH_FROM (g))
             break;
+          need_composition = 1;
           x = metrics.width + LGLYPH_LBEARING (g) + LGLYPH_XOFF (g);
           if (metrics.lbearing > x)
             metrics.lbearing = x;
@@ -3621,20 +3628,25 @@ The value is the end position of the shaped text.  */)
             metrics.width += LGLYPH_WADJUST (g);
         }
 
-      gstr = Ffont_make_gstring (font_object, make_number (j - i));
-      LGSTRING_SET_WIDTH (gstr, metrics.width);
-      LGSTRING_SET_LBEARING (gstr, metrics.lbearing);
-      LGSTRING_SET_RBEARING (gstr, metrics.rbearing);
-      LGSTRING_SET_ASCENT (gstr, metrics.ascent);
-      LGSTRING_SET_DESCENT (gstr, metrics.descent);
-      for (k = i; i < j; i++)
-        LGSTRING_SET_GLYPH (gstr, i - k, LGSTRING_GLYPH (gstring, i));
-      from = make_number (start + this_from);
-      to = make_number (start + this_to);
-      if (NILP (string))
-        Fcompose_region_internal (from, to, gstr, Qnil);
+      if (need_composition)
+        {
+          gstr = Ffont_make_gstring (font_object, make_number (j - i));
+          LGSTRING_SET_WIDTH (gstr, metrics.width);
+          LGSTRING_SET_LBEARING (gstr, metrics.lbearing);
+          LGSTRING_SET_RBEARING (gstr, metrics.rbearing);
+          LGSTRING_SET_ASCENT (gstr, metrics.ascent);
+          LGSTRING_SET_DESCENT (gstr, metrics.descent);
+          for (k = i; i < j; i++)
+            LGSTRING_SET_GLYPH (gstr, i - k, LGSTRING_GLYPH (gstring, i));
+          from = make_number (start + this_from);
+          to = make_number (start + this_to);
+          if (NILP (string))
+            Fcompose_region_internal (from, to, gstr, Qnil);
+          else
+            Fcompose_string_internal (string, from, to, gstr, Qnil);
+        }
       else
-        Fcompose_string_internal (string, from, to, gstr, Qnil);
+        i = j;
     }
 
   return to;