Add hb_font_[sg]et_ptem() to set/get point size on font

New API:
hb_font_set_ptem()
hb_font_get_ptem()

Needed for hb-coretext optical sizing:
https://github.com/behdad/harfbuzz/issues/360

docs/harfbuzz-sections.txt

@@ -246,6 +246,7 @@ hb_font_get_nominal_glyph
 hb_font_get_nominal_glyph_func_t
 hb_font_get_parent
 hb_font_get_ppem
+hb_font_get_ptem
 hb_font_get_scale
 hb_font_get_user_data
 hb_font_get_variation_glyph
@@ -261,6 +262,7 @@ hb_font_set_funcs
 hb_font_set_funcs_data
 hb_font_set_parent
 hb_font_set_ppem
+hb_font_set_ptem
 hb_font_set_scale
 hb_font_set_user_data
 hb_variation_t

src/hb-font-private.hh

@@ -108,6 +108,8 @@ struct hb_font_t {
   unsigned int x_ppem;
   unsigned int y_ppem;
 
+  float ptem;
+
   /* Font variation coordinates. */
   unsigned int num_coords;
   int *coords;
@@ -123,7 +125,8 @@ struct hb_font_t {
     DIRTY_FUNCS		= 0x0004,
     DIRTY_SCALE		= 0x0008,
     DIRTY_PPEM		= 0x0010,
-    DIRTY_VARIATIONS	= 0x0020,
+    DIRTY_PTEM		= 0x0020,
+    DIRTY_VARIATIONS	= 0x0040,
   } dirty;
 
   struct hb_shaper_data_t shaper_data;

src/hb-font.cc

@@ -1157,6 +1157,7 @@ hb_font_create_sub_font (hb_font_t *parent)
   font->y_scale = parent->y_scale;
   font->x_ppem = parent->x_ppem;
   font->y_ppem = parent->y_ppem;
+  font->ptem = parent->ptem;
 
   font->num_coords = parent->num_coords;
   if (!font->num_coords)
@@ -1199,6 +1200,7 @@ hb_font_get_empty (void)
 
     0, /* x_ppem */
     0, /* y_ppem */
+    -1, /* ptem */
 
     0, /* num_coords */
     NULL, /* coords */
@@ -1597,6 +1599,45 @@ hb_font_get_ppem (hb_font_t *font,
   if (y_ppem) *y_ppem = font->y_ppem;
 }
 
+/**
+ * hb_font_set_ptem:
+ * @font: a font.
+ * @ptem: 
+ *
+ * Sets "point size" of the font.
+ *
+ * Since: 1.6.0
+ **/
+void
+hb_font_set_ptem (hb_font_t *font, float ptem)
+{
+  if (font->immutable)
+    return;
+
+  if (font->ptem == ptem)
+    return;
+
+  font->dirty |= font->DIRTY_PTEM;
+
+  font->ptem = ptem;
+}
+
+/**
+ * hb_font_get_ptem:
+ * @font: a font.
+ *
+ * Gets the "point size" of the font.  A value of -1 means unset.
+ *
+ * Return value: Point size.
+ *
+ * Since: 0.9.2
+ **/
+float
+hb_font_get_ptem (hb_font_t *font)
+{
+  return font->ptem;
+}
+
 /*
  * Variations
  */

src/hb-font.h

@@ -607,6 +607,16 @@ hb_font_get_ppem (hb_font_t *font,
 		  unsigned int *x_ppem,
 		  unsigned int *y_ppem);
 
+/*
+ * Point size per EM.  Used for optical-sizing in CoreText.
+ * A -1 means "not set".
+ */
+HB_EXTERN void
+hb_font_set_ptem (hb_font_t *font, float ptem);
+
+HB_EXTERN float
+hb_font_get_ptem (hb_font_t *font);
+
 HB_EXTERN void
 hb_font_set_variations (hb_font_t *font,
 			const hb_variation_t *variations,