[pango/synthetic-slant: 2/2] Pass synthetic slant to harfbuzz

[Matthias Clasen <matthiasc src gnome org>]

commit 1c0b2977a9af7249aa58124f7084b91a94d5e16b
Author: Matthias Clasen <mclasen redhat com>
Date:   Sat Sep 11 12:44:29 2021 -0400

    Pass synthetic slant to harfbuzz
    
    When our font matrix includes a slant, pass that information
    to HarfBuzz, so it can adjust its mark positioning, metrics
    like caret slope, etc.
    
    This commit corrects the code that pulls the font matrix out
    of fontconfig to properly take the flipped y axis between fontconfig
    and pango into account.
    
    Requires new api in HarfBuzz > 3.2

 pango/pangofc-font.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)
---
diff --git a/pango/pangofc-font.c b/pango/pangofc-font.c
index 77e99e16..fb1cbce0 100644
--- a/pango/pangofc-font.c
+++ b/pango/pangofc-font.c
@@ -950,10 +950,12 @@ pango_fc_font_create_hb_font (PangoFont *font)
   double x_scale, y_scale;
   double pixel_size;
   double point_size;
+  double slant;
 
   x_scale_inv = y_scale_inv = 1.0;
   pixel_size = 1.0;
   point_size = 1.0;
+  slant = 0.0;
 
   key = _pango_fc_font_get_font_key (fc_font);
   if (key)
@@ -974,11 +976,12 @@ pango_fc_font_create_hb_font (PangoFont *font)
         FcMatrixMultiply (&fc_matrix, &fc_matrix, fc_matrix_val);
 
       font_matrix.xx = fc_matrix.xx;
-      font_matrix.yx = fc_matrix.yx;
+      font_matrix.yx = - fc_matrix.yx;
       font_matrix.xy = fc_matrix.xy;
-      font_matrix.yy = fc_matrix.yy;
+      font_matrix.yy = - fc_matrix.yy;
 
       pango_matrix_get_font_scale_factors (&font_matrix, &x, &y);
+      slant = pango_matrix_get_slant_ratio (&font_matrix);
 
       x_scale_inv /= x;
       y_scale_inv /= y;
@@ -989,6 +992,7 @@ pango_fc_font_create_hb_font (PangoFont *font)
           x_scale_inv = -x_scale_inv;
           y_scale_inv = -y_scale_inv;
         }
+
       get_font_size (key, &pixel_size, &point_size);
     }
 
@@ -1003,6 +1007,8 @@ pango_fc_font_create_hb_font (PangoFont *font)
                      pixel_size * PANGO_SCALE * y_scale);
   hb_font_set_ptem (hb_font, point_size);
 
+  hb_font_set_synthetic_slant (hb_font, slant);
+
   if (key)
     {
       const FcPattern *pattern = pango_fc_font_key_get_pattern (key);