shape: Bring back careful rounding codebring-back-better-rounding

When we added the round-glyph-positions option in
c43da2d3 and b5634799, we lost some code that was careful
to round in device coordinates.

The reason we lost it is that the rounding needs fontconfig-
specific data that is only available in the backend, and the
rounding now happens in the frontend.

Bringing it back is annoying, since we've run out of vfunc
slots to get info from the backend. This commit works around
that limitation in a hacky way.

Fixes: #562

1 files changed, 73 insertions, 4 deletions

diff --git a/pango/shape.c b/pango/shape.c
index 04407732..b870ecad 100644
--- a/pango/shape.c
+++ b/pango/shape.c
@@ -151,6 +151,32 @@ fallback_shape (const char          *text,
     pango_glyph_string_reverse_range (glyphs, 0, glyphs->num_glyphs);
 }
 
+/* FIXME: This is very ugly. We are out of room for vfuncs, so we can't
+ * easily add api to get is_hinted and the matrix from the PangoFcFont.
+ *
+ * Keep in sync with pangofc-font.h!
+ */
+struct _PangoFcFont
+{
+  PangoFont parent_instance;
+
+  gpointer font_pattern;          /* fully resolved pattern */
+  PangoFontMap *fontmap;            /* associated map */
+  gpointer priv;                    /* used internally */
+  PangoMatrix matrix;               /* used internally */
+  PangoFontDescription *description;
+
+  GSList *metrics_by_lang;
+
+  guint is_hinted : 1;
+  guint is_transformed : 1;
+};
+typedef struct _PangoFcFont PangoFcFont;
+
+#define PANGO_IS_FC_FONT(obj) \
+  g_type_is_a (((GTypeInstance*)obj)->g_class->g_type, \
+               g_type_from_name ("PangoFcFont"))
+
 /**
  * pango_shape_with_flags:
  * @item_text: valid UTF-8 text to shape
@@ -294,11 +320,54 @@ pango_shape_with_flags (const gchar         *item_text,
 
   if (flags & PANGO_SHAPE_ROUND_POSITIONS)
     {
-      for (i = 0; i < glyphs->num_glyphs; i++)
+      if (PANGO_IS_FC_FONT (analysis->font))
         {
-          glyphs->glyphs[i].geometry.width    = PANGO_UNITS_ROUND (glyphs->glyphs[i].geometry.width );
-          glyphs->glyphs[i].geometry.x_offset = PANGO_UNITS_ROUND (glyphs->glyphs[i].geometry.x_offset);
-          glyphs->glyphs[i].geometry.y_offset = PANGO_UNITS_ROUND (glyphs->glyphs[i].geometry.y_offset);
+          PangoFcFont *fc_font = (PangoFcFont *)analysis->font;
+          if (fc_font->is_hinted)
+            {
+              double x_scale_inv, y_scale_inv;
+              double x_scale, y_scale;
+
+              x_scale_inv = y_scale_inv = 1.0;
+              pango_matrix_get_font_scale_factors (&fc_font->matrix, &x_scale_inv, &y_scale_inv);
+              if (PANGO_GRAVITY_IS_IMPROPER (analysis->gravity))
+                {
+                  x_scale_inv = -x_scale_inv;
+                  y_scale_inv = -y_scale_inv;
+                }
+              x_scale = 1. / x_scale_inv;
+              y_scale = 1. / y_scale_inv;
+
+              if (x_scale == 1.0 && y_scale == 1.0)
+                {
+                  for (i = 0; i < glyphs->num_glyphs; i++)
+                    glyphs->glyphs[i].geometry.width = PANGO_UNITS_ROUND (glyphs->glyphs[i].geometry.width);
+                }
+              else
+                {
+    #if 0
+                  if (PANGO_GRAVITY_IS_VERTICAL (analysis->gravity))
+                    {
+                      /* XXX */
+                      double tmp = x_scale;
+                      x_scale = y_scale;
+                      y_scale = -tmp;
+                    }
+    #endif
+    #define HINT(value, scale_inv, scale) (PANGO_UNITS_ROUND ((int) ((value) * scale)) * scale_inv)
+    #define HINT_X(value) HINT ((value), x_scale, x_scale_inv)
+    #define HINT_Y(value) HINT ((value), y_scale, y_scale_inv)
+                  for (i = 0; i < glyphs->num_glyphs; i++)
+                    {
+                      glyphs->glyphs[i].geometry.width    = HINT_X (glyphs->glyphs[i].geometry.width);
+                      glyphs->glyphs[i].geometry.x_offset = HINT_X (glyphs->glyphs[i].geometry.x_offset);
+                      glyphs->glyphs[i].geometry.y_offset = HINT_Y (glyphs->glyphs[i].geometry.y_offset);
+                    }
+    #undef HINT_Y
+    #undef HINT_X
+    #undef HINT
+                }
+            }
         }
     }
 }