[coretext] Fix scaling

Before we were not accounting for possible differences in x_scale and
y_scale, as well as the signs of those.  All should be in good shape
now.

src/hb-coretext.cc

diff --git a/src/hb-coretext.cc b/src/hb-coretext.cc
index 64ceb44..b22c46f 100644
--- a/src/hb-coretext.cc
+++ b/src/hb-coretext.cc
@@ -140,6 +140,7 @@
 
 struct hb_coretext_shaper_font_data_t {
   CTFontRef ct_font;
+  CGFloat x_mult, y_mult; /* From CT space to HB space. */
 };
 
 hb_coretext_shaper_font_data_t *
@@ -154,7 +155,17 @@
   hb_face_t *face = font->face;
   hb_coretext_shaper_face_data_t *face_data = HB_SHAPER_DATA_GET (face);
 
-  data->ct_font = CTFontCreateWithGraphicsFont (face_data, font->y_scale, NULL, NULL);
+  /* Choose a CoreText font size and calculate multipliers to convert to HarfBuzz space. */
+  CGFloat font_size = 36.; /* Default... */
+  /* No idea if the following is even a good idea. */
+  if (font->y_ppem)
+    font_size = font->y_ppem;
+
+  if (font_size < 0)
+    font_size = -font_size;
+  data->x_mult = (CGFloat) font->x_scale / font_size;
+  data->y_mult = (CGFloat) font->y_scale / font_size;
+  data->ct_font = CTFontCreateWithGraphicsFont (face_data, font_size, NULL, NULL);
   if (unlikely (!data->ct_font)) {
     DEBUG_MSG (CORETEXT, font, "Font CTFontCreateWithGraphicsFont() failed");
     free (data);
@@ -956,14 +967,15 @@
 	double run_advance = CTRunGetTypographicBounds (run, range_all, NULL, NULL, NULL);
 	DEBUG_MSG (CORETEXT, run, "Run advance: %g", run_advance);
 	hb_glyph_info_t *info = run_info;
+	CGFloat x_mult = font_data->x_mult, y_mult = font_data->y_mult;
 	if (HB_DIRECTION_IS_HORIZONTAL (buffer->props.direction))
 	{
 	  for (unsigned int j = 0; j < num_glyphs; j++)
 	  {
 	    double advance = (j + 1 < num_glyphs ? positions[j + 1].x : positions[0].x + run_advance) - positions[j].x;
-	    info->mask = advance;
-	    info->var1.u32 = positions[0].x; /* Yes, zero. */
-	    info->var2.u32 = positions[j].y;
+	    info->mask = advance * x_mult;
+	    info->var1.u32 = positions[0].x * x_mult; /* Yes, zero. */
+	    info->var2.u32 = positions[j].y * y_mult;
 	    info++;
 	  }
 	}
@@ -973,9 +985,9 @@
 	  for (unsigned int j = 0; j < num_glyphs; j++)
 	  {
 	    double advance = (j + 1 < num_glyphs ? positions[j + 1].y : positions[0].y + run_advance) - positions[j].y;
-	    info->mask = advance;
-	    info->var1.u32 = positions[j].x;
-	    info->var2.u32 = positions[0].y; /* Yes, zero. */
+	    info->mask = advance * y_mult;
+	    info->var1.u32 = positions[j].x * x_mult;
+	    info->var2.u32 = positions[0].y * y_mult; /* Yes, zero. */
 	    info++;
 	  }
 	}