win32: add synthetic font subsetting support

src/cairo-scaled-font-subsets-private.h

@@ -714,6 +714,29 @@ _cairo_truetype_read_font_name (cairo_scaled_font_t   *scaled_font,
 				char		     **ps_name,
 				char		     **font_name);
 
+/**
+ * _cairo_truetype_get_style:
+ * @scaled_font: the #cairo_scaled_font_t
+ * @weight: returns the font weight from the OS/2 table
+ * @bold: returns true if font is bold
+ * @italic: returns true if font is italic
+ *
+ * If the font is a truetype/opentype font with an OS/2 table, get the
+ * weight, bold, and italic data from the OS/2 table.  The weight
+ * values have the same meaning as the lfWeight field of the Windows
+ * LOGFONT structure.  Refer to the TrueType Specification for
+ * definition of the weight values.
+ *
+ * Return value: %CAIRO_STATUS_SUCCESS if successful,
+ * %CAIRO_INT_STATUS_UNSUPPORTED if the font is not TrueType/OpenType
+ * or the OS/2 table is not present.
+ **/
+cairo_private cairo_int_status_t
+_cairo_truetype_get_style (cairo_scaled_font_t  	 *scaled_font,
+			   int				 *weight,
+			   cairo_bool_t			 *bold,
+			   cairo_bool_t			 *italic);
+
 #endif /* CAIRO_HAS_FONT_SUBSET */
 
 #endif /* CAIRO_SCALED_FONT_SUBSETS_PRIVATE_H */

src/cairo-truetype-subset-private.h

@@ -64,6 +64,7 @@
 #define TT_TAG_loca   MAKE_TT_TAG('l','o','c','a')
 #define TT_TAG_maxp   MAKE_TT_TAG('m','a','x','p')
 #define TT_TAG_name   MAKE_TT_TAG('n','a','m','e')
+#define TT_TAG_OS2    MAKE_TT_TAG('O','S','/','2')
 #define TT_TAG_post   MAKE_TT_TAG('p','o','s','t')
 #define TT_TAG_prep   MAKE_TT_TAG('p','r','e','p')
 
@@ -174,6 +175,18 @@ typedef struct _tt_name {
 } tt_name_t;
 
 
+/* bitmask for fsSelection field */
+#define TT_FS_SELECTION_ITALIC   1
+#define TT_FS_SELECTION_BOLD    32
+
+/* _unused fields are defined in TT spec but not used by cairo */
+typedef struct _tt_os2 {
+    uint16_t   _unused1[2];
+    uint16_t   usWeightClass;
+    uint16_t   _unused2[28];
+    uint16_t   fsSelection;
+    uint16_t   _unused3[11];
+} tt_os2_t;
 
 /* composite_glyph_t flags */
 #define TT_ARG_1_AND_2_ARE_WORDS     0x0001

src/cairo-truetype-subset.c

@@ -1502,4 +1502,36 @@ fail:
     return status;
 }
 
+cairo_int_status_t
+_cairo_truetype_get_style (cairo_scaled_font_t  	 *scaled_font,
+			   int				 *weight,
+			   cairo_bool_t			 *bold,
+			   cairo_bool_t			 *italic)
+{
+    cairo_status_t status;
+    const cairo_scaled_font_backend_t *backend;
+    tt_os2_t os2;
+    unsigned long size;
+    uint16_t selection;
+
+    backend = scaled_font->backend;
+    if (!backend->load_truetype_table)
+	return CAIRO_INT_STATUS_UNSUPPORTED;
+
+    size = sizeof (os2);
+    status = backend->load_truetype_table (scaled_font,
+					   TT_TAG_OS2, 0,
+					   (unsigned char *) &os2,
+					   &size);
+    if (status)
+	return status;
+
+    *weight = be16_to_cpu (os2.usWeightClass);
+    selection = be16_to_cpu (os2.fsSelection);
+    *bold = (selection & TT_FS_SELECTION_BOLD) ? TRUE : FALSE;
+    *italic = (selection & TT_FS_SELECTION_ITALIC) ? TRUE : FALSE;
+
+    return CAIRO_STATUS_SUCCESS;
+}
+
 #endif /* CAIRO_HAS_FONT_SUBSET */

src/cairo-win32-font.c

@@ -46,6 +46,7 @@
 
 #include "cairo-win32-private.h"
 #include "cairo-error-private.h"
+#include "cairo-scaled-font-subsets-private.h"
 
 #include <wchar.h>
 
@@ -1623,6 +1624,31 @@ exit1:
     return status;
 }
 
+static cairo_bool_t
+_cairo_win32_scaled_font_is_synthetic (void	       *abstract_font)
+{
+    cairo_win32_scaled_font_t *scaled_font = abstract_font;
+    cairo_status_t status;
+    int	weight;
+    cairo_bool_t bold;
+    cairo_bool_t italic;
+
+    status = _cairo_truetype_get_style (&scaled_font->base,
+					&weight,
+					&bold,
+					&italic);
+    /* If this doesn't work assume it is not synthetic to avoid
+     * unneccessary subsetting fallbacks. */
+    if (status != CAIRO_STATUS_SUCCESS)
+	return FALSE;
+
+    if (scaled_font->logfont.lfWeight != weight ||
+	scaled_font->logfont.lfItalic != italic)
+	return TRUE;
+
+    return FALSE;
+}
+
 static cairo_status_t
 _cairo_win32_scaled_font_init_glyph_surface (cairo_win32_scaled_font_t *scaled_font,
                                              cairo_scaled_glyph_t      *scaled_glyph)
@@ -1871,6 +1897,7 @@ const cairo_scaled_font_backend_t _cairo_win32_scaled_font_backend = {
     _cairo_win32_scaled_font_show_glyphs,
     _cairo_win32_scaled_font_load_truetype_table,
     _cairo_win32_scaled_font_index_to_ucs4,
+    _cairo_win32_scaled_font_is_synthetic
 };
 
 /* #cairo_win32_font_face_t */