Implement drawing text with DirectWrite on MS-Windows.

This adds support for color fonts.
* configure.ac: Add src/w32drite to W32_OBJ.
* src/w32dwrite.c: New file.
(w32-initialize-direct-write): New function, initialize the
DirectWrite library if it is available, and required global
variables.
(w32_use_direct_write): New function, check if DirectWrite
is available and activated by the user.
(w32_dwrite_encode_char): New function, replacement for HarfBuzz's
'encode_char'.
(w32_dwrite_text_extents): New function, replacement for w32font
text_extents.
(w32_dwrite_draw): New function, replacement for w32font draw.
(w32_dwrite_free_cached_face): New function, used in the font
deletion process to also delete DirectWrite data.
(verify_hr): New function, verify COM method results.
(release_com): New function, release a COM object.
(w32-dwrite-available): New function, returns true if DirectWrite
is available.
(w32-dwrite-reinit): New function, reinitialize DirectWrite,
optionally setting some rendering parameters.
* src/w32font.c (w32font_text_extents): If DirectWrite is enabled,
call 'w32_dwrite_text_extents'.
(w32font_draw): If DirectWrite is enabled, call 'w32_dwrite_draw'.
* src/w32uniscribe.c: (w32hb_encode_char): If DirectWrite is enabled,
call 'w32_dwrite_encode_char'.
(syms_of_w32uniscribe_for_pdumper): Initialize DirectWrite.
(uniscribe_close): Free DirectWrite data for the font.

Bug#73730

configure.ac

@@ -3172,7 +3172,7 @@ if test "${HAVE_W32}" = "yes"; then
   AC_CHECK_TOOL([WINDRES], [windres],
                 [AC_MSG_ERROR([No resource compiler found.])])
   W32_OBJ="w32fns.o w32menu.o w32reg.o w32font.o w32term.o"
-  W32_OBJ="$W32_OBJ w32xfns.o w32select.o w32uniscribe.o w32cygwinx.o"
+  W32_OBJ="$W32_OBJ w32xfns.o w32select.o w32uniscribe.o w32dwrite.o w32cygwinx.o"
   EMACSRES="emacs.res"
   case "$canonical" in
     x86_64-*-*) EMACS_MANIFEST="emacs-x64.manifest" ;;

etc/NEWS

@@ -785,6 +785,14 @@ This is in addition to drag-n-drop of files, that was already
 supported.  As on X, the user options 'dnd-scroll-margin' and
 'dnd-indicate-insertion-point' can be used to customize the process.
 
+---
+** Emacs on MS-Windows now supports color fonts.
+On Windows 8.1 and later versions Emacs now uses DirectWrite to draw
+text, which supports color fonts.  This can be disabled by setting the
+variable 'w32-inhibit-dwrite' to t.  Also see 'w32-dwrite-available' and
+'w32-dwrite-reinit' to check availability and to configure render
+parameters.
+
 
 ----------------------------------------------------------------------
 This file is part of GNU Emacs.

src/w32font.c

@@ -452,6 +452,10 @@ w32font_text_extents (struct font *font, const unsigned *code,
 
   memset (metrics, 0, sizeof (struct font_metrics));
 
+  if (w32_use_direct_write (w32_font))
+      if (w32_dwrite_text_extents (font, code, nglyphs, metrics))
+	return;
+
   for (i = 0, first = true; i < nglyphs; i++)
     {
       struct w32_metric_cache *char_metric;
@@ -706,22 +710,31 @@ w32font_draw (struct glyph_string *s, int from, int to,
       int i;
 
       for (i = 0; i < len; i++)
-	{
-	  WCHAR c = s->char2b[from + i] & 0xFFFF;
-	  ExtTextOutW (s->hdc, x + i, y, options, NULL, &c, 1, NULL);
-	}
+	if (!w32_use_direct_write (w32font) ||
+	    !w32_dwrite_draw (s->hdc, x, y, s->char2b + from, 1,
+			      GetTextColor(s->hdc), s->font))
+	  {
+	    WCHAR c = s->char2b[from + i] & 0xFFFF;
+	    ExtTextOutW (s->hdc, x + i, y, options, NULL, &c, 1, NULL);
+	  }
     }
   else
     {
-      /* The number of glyphs in a glyph_string cannot be larger than
-	 the maximum value of the 'used' member of a glyph_row, so we
-	 are OK using alloca here.  */
-      eassert (len <= SHRT_MAX);
-      WCHAR *chars = alloca (len * sizeof (WCHAR));
-      int j;
-      for (j = 0; j < len; j++)
-	chars[j] = s->char2b[from + j] & 0xFFFF;
-      ExtTextOutW (s->hdc, x, y, options, NULL, chars, len, NULL);
+      if (!w32_use_direct_write (w32font) ||
+	  !w32_dwrite_draw (s->hdc, x, y,
+			    s->char2b + from, len, GetTextColor(s->hdc),
+			    s->font))
+	{
+	  /* The number of glyphs in a glyph_string cannot be larger than
+	     the maximum value of the 'used' member of a glyph_row, so we
+	     are OK using alloca here.  */
+	  eassert (len <= SHRT_MAX);
+	  WCHAR *chars = alloca (len * sizeof (WCHAR));
+	  int j;
+	  for (j = 0; j < len; j++)
+	    chars[j] = s->char2b[from + j] & 0xFFFF;
+	  ExtTextOutW (s->hdc, x, y, options, NULL, chars, len, NULL);
+	}
     }
 
   /* Restore clip region.  */

src/w32font.h

@@ -57,6 +57,26 @@ struct w32font_info
   HFONT hfont;
 };
 
+/* Extension of w32font_info used by Uniscribe and HarfBuzz backends.  */
+struct uniscribe_font_info
+{
+  struct w32font_info w32_font;
+  /* This is used by the Uniscribe backend as a pointer to the script
+     cache, and by the HarfBuzz backend as a pointer to a hb_font_t
+     object.  */
+  void *cache;
+  /* This is used by the HarfBuzz backend to store the font scale.  */
+  double scale;
+  /* This is used by DirectWrite to store the FontFace object.
+     DirectWrite works on top of the HarfBuzz backend, modifying some
+     calls.  If there are problems manipulating this font,
+     dwrite_skip_font is set to true.  Future operations will not use
+     DirectWrite and fall back to the HarfBuzz backend.  */
+  void *dwrite_cache;
+  float dwrite_font_size;
+  bool dwrite_skip_font;
+};
+
 /* Macros for getting OS specific information from a font struct.  */
 #define FONT_HANDLE(f) (((struct w32font_info *)(f))->hfont)
 #define FONT_TEXTMETRIC(f) (((struct w32font_info *)(f))->metrics)
@@ -84,6 +104,17 @@ int uniscribe_check_otf (LOGFONT *font, Lisp_Object otf_spec);
 
 Lisp_Object intern_font_name (char *);
 
+/* Function prototypes for DirectWrite.  */
+void w32_initialize_direct_write (void);
+bool w32_use_direct_write (struct w32font_info *w32font);
+bool w32_dwrite_draw (HDC hdc, int x, int y, unsigned *glyphs, int len,
+		      COLORREF color, struct font *font );
+bool w32_dwrite_text_extents (struct font *font, const unsigned *code,
+			      int nglyphs, struct font_metrics *metrics);
+unsigned w32_dwrite_encode_char (struct font *font, int c);
+void w32_dwrite_free_cached_face(void *cache);
+void syms_of_w32dwrite (void);
+
 extern void globals_of_w32font (void);
 
 #endif

src/w32uniscribe.c

@@ -44,18 +44,6 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */
 #include "pdumper.h"
 #include "w32common.h"
 
-/* Extension of w32font_info used by Uniscribe and HarfBuzz backends.  */
-struct uniscribe_font_info
-{
-  struct w32font_info w32_font;
-  /* This is used by the Uniscribe backend as a pointer to the script
-     cache, and by the HarfBuzz backend as a pointer to a hb_font_t
-     object.  */
-  void *cache;
-  /* This is used by the HarfBuzz backend to store the font scale.  */
-  double scale;
-};
-
 int uniscribe_available = 0;
 
 /* EnumFontFamiliesEx callback.  */
@@ -200,6 +188,9 @@ uniscribe_open (struct frame *f, Lisp_Object font_entity, int pixel_size)
 
   /* Initialize the cache for this font.  */
   uniscribe_font->cache = NULL;
+  uniscribe_font->dwrite_cache = NULL;
+
+  uniscribe_font->dwrite_skip_font = false;
 
   /* Uniscribe and HarfBuzz backends use glyph indices.  */
   uniscribe_font->w32_font.glyph_idx = ETO_GLYPH_INDEX;
@@ -221,6 +212,7 @@ uniscribe_close (struct font *font)
     = (struct uniscribe_font_info *) font;
 
 #ifdef HAVE_HARFBUZZ
+  w32_dwrite_free_cached_face (uniscribe_font->dwrite_cache);
   if (uniscribe_font->w32_font.font.driver == &harfbuzz_font_driver
       && uniscribe_font->cache)
     hb_font_destroy ((hb_font_t *) uniscribe_font->cache);
@@ -1372,6 +1364,17 @@ w32hb_encode_char (struct font *font, int c)
   struct uniscribe_font_info *uniscribe_font
     = (struct uniscribe_font_info *) font;
   eassert (uniscribe_font->w32_font.font.driver == &harfbuzz_font_driver);
+
+  if (w32_use_direct_write (&uniscribe_font->w32_font))
+    {
+      unsigned encoded = w32_dwrite_encode_char (font, c);
+
+      /* The call to w32_dwrite_encode_char may fail, disabling
+	 DirectWrite for this font.  So check again.  */
+      if (w32_use_direct_write (&uniscribe_font->w32_font))
+	return encoded;
+    }
+
   hb_font_t *hb_font = uniscribe_font->cache;
 
   /* First time we use this font with HarfBuzz, create the hb_font_t
@@ -1510,6 +1513,7 @@ static void syms_of_w32uniscribe_for_pdumper (void);
 void
 syms_of_w32uniscribe (void)
 {
+  syms_of_w32dwrite ();
   pdumper_do_now_and_after_load (syms_of_w32uniscribe_for_pdumper);
 }
 
@@ -1624,5 +1628,8 @@ syms_of_w32uniscribe_for_pdumper (void)
   harfbuzz_font_driver.combining_capability = hbfont_combining_capability;
   harfbuzz_font_driver.begin_hb_font = w32hb_begin_font;
   register_font_driver (&harfbuzz_font_driver, NULL);
+
+  w32_initialize_direct_write ();
+
 #endif	/* HAVE_HARFBUZZ */
 }