[pango/fix-font-roundtrip: 2/3] Fix pango_font_describe for Emoji fonts

[Matthias Clasen <matthiasc src gnome org>]

commit bc5ad5e8d536ed4e8c9f98a1e60f3ba3fe2458aa
Author: Matthias Clasen <mclasen redhat com>
Date:   Sun Jan 24 11:15:01 2021 -0500

    Fix pango_font_describe for Emoji fonts
    
    We are using the size from the FcPattern. For scalable
    bitmap fonts, this has been scaled to match the requested
    pixel size. To make a font description that can be turned
    back into a FcPattern and roundtrip successfully, we need
    to undo that scaling. Thankfully, fontconfig leaves the
    pixelsizefixupfactor in the pattern, so it is easy to do.
    
    Fixes: #530

 pango/pangofc-fontmap.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)
---
diff --git a/pango/pangofc-fontmap.c b/pango/pangofc-fontmap.c
index 764336ae..170b3e5c 100644
--- a/pango/pangofc-fontmap.c
+++ b/pango/pangofc-fontmap.c
@@ -2519,7 +2519,14 @@ pango_fc_font_description_from_pattern (FcPattern *pattern, gboolean include_siz
   pango_font_description_set_variant (desc, PANGO_VARIANT_NORMAL);
 
   if (include_size && FcPatternGetDouble (pattern, FC_SIZE, 0, &size) == FcResultMatch)
-    pango_font_description_set_size (desc, size * PANGO_SCALE);
+    {
+      double pixelsizefixupfactor;
+
+      if (FcPatternGetDouble (pattern, "pixelsizefixupfactor", 0, &pixelsizefixupfactor) != FcResultMatch)
+        pixelsizefixupfactor = 1;
+
+      pango_font_description_set_size (desc, pixelsizefixupfactor * size * PANGO_SCALE);
+    }
 
   /* gravity is a bit different.  we don't want to set it if it was not set on
    * the pattern */