[pango/hinting] cairo: Adjust hinting to subpixel positioning

[Matthias Clasen <matthiasc src gnome org>]

commit 3d8f685443e6f0ddac7f3e7402169cf82ea79d88
Author: Matthias Clasen <mclasen redhat com>
Date:   Sat Aug 24 14:50:26 2019 +0200

    cairo: Adjust hinting to subpixel positioning
    
    If we are not rounding glyph positions, assume we are
    doing subpixel positioning, and reduce the hint style
    to slight hinting and turn metrics hinting off.

 pango/pangocairo-context.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)
---
diff --git a/pango/pangocairo-context.c b/pango/pangocairo-context.c
index 5949c448..e8b8cc5d 100644
--- a/pango/pangocairo-context.c
+++ b/pango/pangocairo-context.c
@@ -321,6 +321,22 @@ _pango_cairo_context_get_merged_font_options (PangoContext *context)
        cairo_font_options_merge (info->merged_options, info->surface_options);
       if (info->set_options)
        cairo_font_options_merge (info->merged_options, info->set_options);
+
+      if (!pango_context_get_round_glyph_positions (context))
+        {
+          switch (cairo_font_options_get_hint_style (info->merged_options))
+            {
+            case CAIRO_HINT_STYLE_DEFAULT:
+            case CAIRO_HINT_STYLE_NONE:
+            case CAIRO_HINT_STYLE_SLIGHT:
+              break;
+            case CAIRO_HINT_STYLE_MEDIUM:
+            case CAIRO_HINT_STYLE_FULL:
+              cairo_font_options_set_hint_style (info->merged_options, CAIRO_HINT_STYLE_SLIGHT);
+              break;
+            }
+          cairo_font_options_set_hint_metrics (info->merged_options, CAIRO_HINT_METRICS_OFF);
+        }
     }
 
   return info->merged_options;