bug#73730: 31.0.50; Support for color fonts on MS-Windows

[Cecilio Pardo <cpardo@imayhem.com>]

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The attached patch works without a new font driver.

This requires the harfbuzz font backend to be available.

It works by modifying the harfbuzz backend to use DirectWrite at
some points, if it is available:

- When encoding characters: w32hb_encode_char
- When measuring text: w32font_text_extents
- When drawing text: w32font_draw

DirectWrite is setup by calling w32_initialize_direct_write.  From
that point, the function w32_use_direct_write will return true if
DirectWrite is to be used.

The lisp variable w32-inhibit-direct-write can switches it on and off.

It builds with Mingw64 and Mingw. As mingw doesn't have the DirectWrite 
includes, I had to declare a lot of things at the start of the file. 
This line marks the end of that:

/* End of dwrite_3.h definitions.  */

I have tested this only on Windows 11.

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From 608f81421553b087ca7eb822c14b6d889787719b Mon Sep 17 00:00:00 2001
From: Cecilio Pardo <cpardo@imayhem.com>
Date: Wed, 9 Oct 2024 11:40:28 +0200
Subject: [PATCH] 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: This is a new file.
(w32-initialize-direct-write): Initializes the DirectWrite library if
it is available, and required global variables.
(w32_use_direct_write): Allows to check if DirectWrite is available
and activated by the user.
(w32_dwrite_encode_char): Replacement for harfbuzz's encode_char.
(w32_dwrite_text_extents): Replacement for w32font text_extents.
(w32_dwrite_draw): Replacement for w32font draw.
(w32_dwrite_free_cached_face): Used on the font deletion process to
also delete DirectWrite data.
(verify_hr): Verify COM method results.
* 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.
---
 configure.ac       |   2 +-
 src/w32dwrite.c    | 930 +++++++++++++++++++++++++++++++++++++++++++++
 src/w32font.c      |  53 ++-
 src/w32uniscribe.c |  39 ++
 4 files changed, 1010 insertions(+), 14 deletions(-)
 create mode 100644 src/w32dwrite.c

diff --git a/configure.ac b/configure.ac
index 8a5ba7db3d1..ba9cd8f0cd5 100644
--- a/configure.ac
+++ b/configure.ac
@@ -3172,7 +3172,7 @@ AC_DEFUN
   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" ;;
diff --git a/src/w32dwrite.c b/src/w32dwrite.c
new file mode 100644
index 00000000000..cdb61dd7176
--- /dev/null
+++ b/src/w32dwrite.c
@@ -0,0 +1,930 @@
+/* Support for using DirectWrite on MS-Windows to draw text. This allows
+   for color fonts.
+   Copyright (C) 2024 Free Software Foundation, Inc.
+
+This file is part of GNU Emacs.
+
+GNU Emacs is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or (at
+your option) any later version.
+
+GNU Emacs is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */
+
+/*
+  This requires the harfbuzz font backend to be available.
+
+  It works by modifying the harfbuzz backend to use DirectWrite at
+  some points, if it is available:
+
+  - When encoding characters: w32hb_encode_char
+  - When measuring text: w32font_text_extents
+  - When drawing text: w32font_draw
+
+  DirectWrite is setup by calling w32_initialize_direct_write.  From
+  that point, the function w32_use_direct_write will return true if
+  DirectWrite is to be used.  */
+
+
+#include <config.h>
+#include <math.h>
+#include <windows.h>
+
+#include "frame.h"
+#include "w32font.h"
+#include "w32common.h"
+#include "w32term.h"
+
+#include "initguid.h"
+#include <ole2.h>
+#include <unknwn.h>
+
+/* The following definitions would be included from dwrite_3.h, but it
+   is not available when building with MinGW.  Methods that we don't use
+   are declared with the UNUSED macro, to avoid bringing in more types
+   that would need to be declared.
+*/
+
+#define UNUSED(name) void (STDMETHODCALLTYPE *name)(void)
+
+#define DWRITE_E_NOCOLOR _HRESULT_TYPEDEF_(0x8898500CL)
+
+typedef enum DWRITE_PIXEL_GEOMETRY {
+    DWRITE_PIXEL_GEOMETRY_FLAT = 0,
+    DWRITE_PIXEL_GEOMETRY_RGB = 1,
+    DWRITE_PIXEL_GEOMETRY_BGR = 2
+} DWRITE_PIXEL_GEOMETRY;
+
+typedef enum DWRITE_RENDERING_MODE {
+    DWRITE_RENDERING_MODE_DEFAULT = 0,
+    DWRITE_RENDERING_MODE_ALIASED = 1,
+    DWRITE_RENDERING_MODE_GDI_CLASSIC = 2,
+    DWRITE_RENDERING_MODE_GDI_NATURAL = 3,
+    DWRITE_RENDERING_MODE_NATURAL = 4,
+    DWRITE_RENDERING_MODE_NATURAL_SYMMETRIC = 5,
+    DWRITE_RENDERING_MODE_OUTLINE = 6
+} DWRITE_RENDERING_MODE;
+
+typedef enum DWRITE_MEASURING_MODE {
+    DWRITE_MEASURING_MODE_NATURAL = 0,
+    DWRITE_MEASURING_MODE_GDI_CLASSIC = 1,
+    DWRITE_MEASURING_MODE_GDI_NATURAL = 2
+} DWRITE_MEASURING_MODE;
+
+typedef enum DWRITE_TEXT_ANTIALIAS_MODE {
+    DWRITE_TEXT_ANTIALIAS_MODE_CLEARTYPE = 0,
+    DWRITE_TEXT_ANTIALIAS_MODE_GRAYSCALE = 1
+} DWRITE_TEXT_ANTIALIAS_MODE;
+
+typedef enum DWRITE_FACTORY_TYPE {
+    DWRITE_FACTORY_TYPE_SHARED = 0,
+    DWRITE_FACTORY_TYPE_ISOLATED = 1
+} DWRITE_FACTORY_TYPE;
+
+typedef struct DWRITE_FONT_METRICS {
+    UINT16 designUnitsPerEm;
+    UINT16 ascent;
+    UINT16 descent;
+    INT16 lineGap;
+    UINT16 capHeight;
+    UINT16 xHeight;
+    INT16 underlinePosition;
+    UINT16 underlineThickness;
+    INT16 strikethroughPosition;
+    UINT16 strikethroughThickness;
+} DWRITE_FONT_METRICS;
+
+typedef struct DWRITE_GLYPH_METRICS {
+    INT32 leftSideBearing;
+    UINT32 advanceWidth;
+    INT32 rightSideBearing;
+    INT32 topSideBearing;
+    UINT32 advanceHeight;
+    INT32 bottomSideBearing;
+    INT32 verticalOriginY;
+} DWRITE_GLYPH_METRICS;
+
+typedef interface IDWriteRenderingParams IDWriteRenderingParams;
+typedef interface IDWriteFont IDWriteFont;
+typedef interface IDWriteGdiInterop IDWriteGdiInterop;
+typedef interface IDWriteFactory IDWriteFactory;
+typedef interface IDWriteFactory2 IDWriteFactory2;
+typedef interface IDWriteFontFace IDWriteFontFace;
+typedef interface IDWriteBitmapRenderTarget IDWriteBitmapRenderTarget;
+typedef interface IDWriteBitmapRenderTarget1 IDWriteBitmapRenderTarget1;
+typedef interface IDWriteColorGlyphRunEnumerator IDWriteColorGlyphRunEnumerator;
+
+DEFINE_GUID(IID_IDWriteBitmapRenderTarget1, 0x791e8298, 0x3ef3, 0x4230, 0x98,0x80, 0xc9,0xbd,0xec,0xc4,0x20,0x64);
+DEFINE_GUID(IID_IDWriteFactory2, 0x0439fc60, 0xca44, 0x4994, 0x8d,0xee, 0x3a,0x9a,0xf7,0xb7,0x32,0xec);
+DEFINE_GUID(IID_IDWriteFactory, 0xb859ee5a, 0xd838, 0x4b5b, 0xa2,0xe8, 0x1a,0xdc,0x7d,0x93,0xdb,0x48);
+
+typedef struct DWRITE_GLYPH_OFFSET {
+    FLOAT advanceOffset;
+    FLOAT ascenderOffset;
+} DWRITE_GLYPH_OFFSET;
+
+typedef struct DWRITE_GLYPH_RUN {
+    IDWriteFontFace *fontFace;
+    FLOAT fontEmSize;
+    UINT32 glyphCount;
+    const UINT16 *glyphIndices;
+    const FLOAT *glyphAdvances;
+    const DWRITE_GLYPH_OFFSET *glyphOffsets;
+    WINBOOL isSideways;
+    UINT32 bidiLevel;
+}  DWRITE_GLYPH_RUN;
+
+typedef struct _D3DCOLORVALUE {
+  float r;
+  float g;
+  float b;
+  float a;
+} D3DCOLORVALUE;
+
+typedef D3DCOLORVALUE DWRITE_COLOR_F;
+
+typedef struct DWRITE_COLOR_GLYPH_RUN {
+    DWRITE_GLYPH_RUN glyphRun;
+    void *glyphRunDescription;
+    FLOAT baselineOriginX;
+    FLOAT baselineOriginY;
+    DWRITE_COLOR_F runColor;
+    UINT16 paletteIndex;
+} DWRITE_COLOR_GLYPH_RUN;
+
+
+typedef struct IDWriteFontFaceVtbl {
+  BEGIN_INTERFACE
+
+  HRESULT (STDMETHODCALLTYPE *QueryInterface)
+    (IDWriteFontFace *This, REFIID riid, void **ppvObject);
+  ULONG (STDMETHODCALLTYPE *AddRef)(IDWriteFontFace *This);
+  ULONG (STDMETHODCALLTYPE *Release)(IDWriteFontFace *This);
+
+  UNUSED(GetType);
+  UNUSED(GetFiles);
+  UNUSED(GetIndex);
+  UNUSED(GetSimulations);
+  UNUSED(IsSymbolFont);
+
+  void (STDMETHODCALLTYPE *GetMetrics)
+    (IDWriteFontFace *This, DWRITE_FONT_METRICS *metrics);
+
+  UNUSED (GetGlyphCount);
+  UNUSED (GetDesignGlyphMetrics);
+
+  HRESULT (STDMETHODCALLTYPE *GetGlyphIndices)
+    (IDWriteFontFace *This, const UINT32 *codepoints, UINT32 count,
+     UINT16 *glyph_indices);
+
+  UNUSED (TryGetFontTable);
+  UNUSED (ReleaseFontTable);
+  UNUSED (GetGlyphRunOutline);
+  UNUSED (GetRecommendedRenderingMode);
+  UNUSED (GetGdiCompatibleMetrics);
+
+  HRESULT (STDMETHODCALLTYPE *GetGdiCompatibleGlyphMetrics)
+    (IDWriteFontFace *This,
+     FLOAT emSize,
+     FLOAT pixels_per_dip,
+     void *transform,
+     WINBOOL use_gdi_natural,
+     const UINT16 *glyph_indices,
+     UINT32 glyph_count,
+     DWRITE_GLYPH_METRICS *metrics,
+     WINBOOL is_sideways);
+  END_INTERFACE
+} IDWriteFontFaceVtbl;
+
+interface IDWriteFontFace {
+    CONST_VTBL IDWriteFontFaceVtbl* lpVtbl;
+};
+
+typedef struct IDWriteRenderingParamsVtbl {
+  BEGIN_INTERFACE
+
+  HRESULT (STDMETHODCALLTYPE *QueryInterface)
+    (IDWriteRenderingParams *This, REFIID riid, void **ppvObject);
+  ULONG (STDMETHODCALLTYPE *AddRef)(IDWriteRenderingParams *This);
+  ULONG (STDMETHODCALLTYPE *Release)(IDWriteRenderingParams *This);
+
+  FLOAT (STDMETHODCALLTYPE *GetGamma)
+    (IDWriteRenderingParams *This);
+  FLOAT (STDMETHODCALLTYPE *GetEnhancedContrast)
+    (IDWriteRenderingParams *This);
+  FLOAT (STDMETHODCALLTYPE *GetClearTypeLevel)
+    (IDWriteRenderingParams *This);
+  int (STDMETHODCALLTYPE *GetPixelGeometry)
+    (IDWriteRenderingParams *This);
+  END_INTERFACE
+} IDWriteRenderingParamsVtbl;
+
+interface IDWriteRenderingParams {
+    CONST_VTBL IDWriteRenderingParamsVtbl* lpVtbl;
+};
+
+typedef struct IDWriteFontVtbl {
+  BEGIN_INTERFACE
+
+  HRESULT (STDMETHODCALLTYPE *QueryInterface)
+    (IDWriteFont *This, REFIID riid, void **ppvObject);
+  ULONG (STDMETHODCALLTYPE *AddRef)(IDWriteFont *This);
+  ULONG (STDMETHODCALLTYPE *Release)(IDWriteFont *This);
+
+  UNUSED (GetFontFamily);
+  UNUSED (GetWeight);
+  UNUSED (GetStretch);
+  UNUSED (GetStyle);
+  UNUSED (IsSymbolFont);
+  UNUSED (GetFaceNames);
+  UNUSED (GetInformationalStrings);
+  UNUSED (GetSimulations);
+
+  void (STDMETHODCALLTYPE *GetMetrics)
+    (IDWriteFont *This, DWRITE_FONT_METRICS *metrics);
+
+  UNUSED(HasCharacter);
+
+  HRESULT (STDMETHODCALLTYPE *CreateFontFace)
+    (IDWriteFont *This, IDWriteFontFace **face);
+
+  END_INTERFACE
+} IDWriteFontVtbl;
+
+interface IDWriteFont {
+    CONST_VTBL IDWriteFontVtbl* lpVtbl;
+};
+
+typedef struct IDWriteBitmapRenderTargetVtbl {
+  BEGIN_INTERFACE
+
+  HRESULT (STDMETHODCALLTYPE *QueryInterface)
+    (IDWriteBitmapRenderTarget *This, REFIID riid, void **ppvObject);
+  ULONG (STDMETHODCALLTYPE *AddRef)(IDWriteBitmapRenderTarget *This);
+  ULONG (STDMETHODCALLTYPE *Release)(IDWriteBitmapRenderTarget *This);
+
+  HRESULT (STDMETHODCALLTYPE *DrawGlyphRun)
+    (IDWriteBitmapRenderTarget *This,
+     FLOAT baselineOriginX,
+     FLOAT baselineOriginY,
+     DWRITE_MEASURING_MODE measuring_mode,
+     const DWRITE_GLYPH_RUN *glyph_run,
+     IDWriteRenderingParams *params,
+     COLORREF textColor,
+     RECT *blackbox_rect);
+
+  HDC (STDMETHODCALLTYPE *GetMemoryDC)(IDWriteBitmapRenderTarget *This);
+
+  UNUSED (GetPixelsPerDip);
+
+  HRESULT (STDMETHODCALLTYPE *SetPixelsPerDip)
+    (IDWriteBitmapRenderTarget *This, FLOAT pixels_per_dip);
+
+  UNUSED (GetCurrentTransform);
+  UNUSED (SetCurrentTransform);
+  UNUSED (GetSize);
+  UNUSED (Resize);
+  END_INTERFACE
+} IDWriteBitmapRenderTargetVtbl;
+
+interface IDWriteBitmapRenderTarget {
+    CONST_VTBL IDWriteBitmapRenderTargetVtbl* lpVtbl;
+};
+
+typedef struct IDWriteBitmapRenderTarget1Vtbl {
+  BEGIN_INTERFACE
+
+  HRESULT (STDMETHODCALLTYPE *QueryInterface)
+    (IDWriteBitmapRenderTarget1 *This, REFIID riid, void **ppvObject);
+  ULONG (STDMETHODCALLTYPE *AddRef) (IDWriteBitmapRenderTarget1 *This);
+  ULONG (STDMETHODCALLTYPE *Release) (IDWriteBitmapRenderTarget1 *This);
+
+  UNUSED (DrawGlyphRun);
+  UNUSED (GetMemoryDC);
+  UNUSED (GetPixelsPerDip);
+  UNUSED (SetPixelsPerDip);
+  UNUSED (GetCurrentTransform);
+  UNUSED (SetCurrentTransform);
+  UNUSED (GetSize);
+  UNUSED (Resize);
+  UNUSED (GetTextAntialiasMode);
+
+  HRESULT (STDMETHODCALLTYPE *SetTextAntialiasMode)
+    (IDWriteBitmapRenderTarget1 *This, DWRITE_TEXT_ANTIALIAS_MODE mode);
+
+  END_INTERFACE
+} IDWriteBitmapRenderTarget1Vtbl;
+
+interface IDWriteBitmapRenderTarget1 {
+    CONST_VTBL IDWriteBitmapRenderTarget1Vtbl* lpVtbl;
+};
+
+typedef struct IDWriteGdiInteropVtbl {
+  BEGIN_INTERFACE
+
+  HRESULT (STDMETHODCALLTYPE *QueryInterface)
+    (IDWriteGdiInterop *This, REFIID riid, void **ppvObject);
+  ULONG (STDMETHODCALLTYPE *AddRef)(IDWriteGdiInterop *This);
+  ULONG (STDMETHODCALLTYPE *Release)(IDWriteGdiInterop *This);
+
+  HRESULT (STDMETHODCALLTYPE *CreateFontFromLOGFONT)
+    (IDWriteGdiInterop *This, const LOGFONTW *logfont,
+     IDWriteFont **font);
+
+  UNUSED (ConvertFontToLOGFONT);
+  UNUSED (ConvertFontFaceToLOGFONT);
+  UNUSED (CreateFontFaceFromHdc);
+
+  HRESULT (STDMETHODCALLTYPE *CreateBitmapRenderTarget)
+    (IDWriteGdiInterop *This, HDC hdc, UINT32 width, UINT32 height,
+     IDWriteBitmapRenderTarget **target);
+  END_INTERFACE
+} IDWriteGdiInteropVtbl;
+
+interface IDWriteGdiInterop {
+    CONST_VTBL IDWriteGdiInteropVtbl* lpVtbl;
+};
+
+typedef struct IDWriteFactoryVtbl {
+  BEGIN_INTERFACE
+
+  HRESULT (STDMETHODCALLTYPE *QueryInterface)
+    (IDWriteFactory *This, REFIID riid, void **ppvObject);
+  ULONG (STDMETHODCALLTYPE *AddRef)(IDWriteFactory *This);
+  ULONG (STDMETHODCALLTYPE *Release)(IDWriteFactory *This);
+
+  UNUSED (GetSystemFontCollection);
+  UNUSED (CreateCustomFontCollection);
+  UNUSED (RegisterFontCollectionLoader);
+  UNUSED (UnregisterFontCollectionLoader);
+  UNUSED (CreateFontFileReference);
+  UNUSED (CreateCustomFontFileReference);
+  UNUSED (CreateFontFace);
+  HRESULT (STDMETHODCALLTYPE *CreateRenderingParams)
+    (IDWriteFactory *This, IDWriteRenderingParams **params);
+  UNUSED (CreateMonitorRenderingParams);
+  HRESULT (STDMETHODCALLTYPE *CreateCustomRenderingParams)
+    (IDWriteFactory *This, FLOAT gamma, FLOAT enhancedContrast,
+     FLOAT cleartype_level, DWRITE_PIXEL_GEOMETRY geometry,
+     DWRITE_RENDERING_MODE mode, IDWriteRenderingParams **params);
+  UNUSED (RegisterFontFileLoader);
+  UNUSED (UnregisterFontFileLoader);
+  UNUSED (CreateTextFormat);
+  UNUSED (CreateTypography);
+  HRESULT (STDMETHODCALLTYPE *GetGdiInterop)
+    (IDWriteFactory *This, IDWriteGdiInterop **gdi_interop);
+  UNUSED (CreateTextLayout);
+  UNUSED (CreateGdiCompatibleTextLayout);
+  UNUSED (CreateEllipsisTrimmingSign);
+  UNUSED (CreateTextAnalyzer);
+  UNUSED (CreateNumberSubstitution);
+  UNUSED (CreateGlyphRunAnalysis);
+  END_INTERFACE
+} IDWriteFactoryVtbl;
+
+interface IDWriteFactory { CONST_VTBL IDWriteFactoryVtbl* lpVtbl; };
+
+typedef struct IDWriteColorGlyphRunEnumeratorVtbl {
+    BEGIN_INTERFACE
+
+    HRESULT (STDMETHODCALLTYPE *QueryInterface)
+      (IDWriteColorGlyphRunEnumerator *This, REFIID riid, void **ppvObject);
+    ULONG (STDMETHODCALLTYPE *AddRef)(IDWriteColorGlyphRunEnumerator *This);
+    ULONG (STDMETHODCALLTYPE *Release)(IDWriteColorGlyphRunEnumerator *This);
+
+    HRESULT (STDMETHODCALLTYPE *MoveNext)(
+        IDWriteColorGlyphRunEnumerator *This,
+        WINBOOL *hasRun);
+
+    HRESULT (STDMETHODCALLTYPE *GetCurrentRun)(
+        IDWriteColorGlyphRunEnumerator *This,
+        const DWRITE_COLOR_GLYPH_RUN **run);
+
+    END_INTERFACE
+} IDWriteColorGlyphRunEnumeratorVtbl;
+
+interface IDWriteColorGlyphRunEnumerator {
+    CONST_VTBL IDWriteColorGlyphRunEnumeratorVtbl* lpVtbl;
+};
+
+typedef struct IDWriteFactory2Vtbl {
+  BEGIN_INTERFACE
+  HRESULT (STDMETHODCALLTYPE *QueryInterface)
+      (IDWriteFactory2 *This, REFIID riid, void **ppvObject);
+  ULONG (STDMETHODCALLTYPE *AddRef)(IDWriteFactory2 *This);
+  ULONG (STDMETHODCALLTYPE *Release)(IDWriteFactory2 *This);
+  UNUSED (GetSystemFontCollection);
+  UNUSED (CreateCustomFontCollection);
+  UNUSED (RegisterFontCollectionLoader);
+  UNUSED (UnregisterFontCollectionLoader);
+  UNUSED (CreateFontFileReference);
+  UNUSED (CreateCustomFontFileReference);
+  UNUSED (CreateFontFace);
+  UNUSED (CreateRenderingParams);
+  UNUSED (CreateMonitorRenderingParams);
+  UNUSED (CreateCustomRenderingParams);
+  UNUSED (RegisterFontFileLoader);
+  UNUSED (UnregisterFontFileLoader);
+  UNUSED (CreateTextFormat);
+  UNUSED (CreateTypography);
+  UNUSED (GetGdiInterop);
+  UNUSED (CreateTextLayout);
+  UNUSED (CreateGdiCompatibleTextLayout);
+  UNUSED (CreateEllipsisTrimmingSign);
+  UNUSED (CreateTextAnalyzer);
+  UNUSED (CreateNumberSubstitution);
+  UNUSED (CreateGlyphRunAnalysis);
+
+  UNUSED (GetEudcFontCollection);
+  UNUSED (IDWriteFactory1_CreateCustomRenderingParams);
+
+  UNUSED (GetSystemFontFallback);
+  UNUSED (CreateFontFallbackBuilder);
+  HRESULT (STDMETHODCALLTYPE *TranslateColorGlyphRun)
+    (IDWriteFactory2 *This,
+     FLOAT originX,
+     FLOAT originY,
+     const DWRITE_GLYPH_RUN *run,
+     void *rundescr,
+     DWRITE_MEASURING_MODE mode,
+     void *transform,
+     UINT32 palette_index,
+     IDWriteColorGlyphRunEnumerator **colorlayers);
+
+  UNUSED (IDWriteFactory2_CreateCustomRenderingParams);
+  UNUSED (IDWriteFactory2_CreateGlyphRunAnalysis);
+  END_INTERFACE
+} IDWriteFactory2Vtbl;
+
+interface IDWriteFactory2 {
+    CONST_VTBL IDWriteFactory2Vtbl* lpVtbl;
+};
+
+/* End of dwrite_3.h definitions.  */
+
+/* Values to use for DirectWrite rendering.  */
+#define MEASURING_MODE DWRITE_MEASURING_MODE_NATURAL
+#define RENDERING_MODE DWRITE_RENDERING_MODE_NATURAL_SYMMETRIC
+#define ANTIALIAS_MODE DWRITE_TEXT_ANTIALIAS_MODE_CLEARTYPE
+
+#define RELEASE_COM(i) (i)->lpVtbl->Release (i)
+
+/* Global variables for DirectWrite.  */
+static bool direct_write_available = false;
+static IDWriteFactory *dwrite_factory;
+static IDWriteFactory2 *dwrite_factory2;
+static IDWriteGdiInterop *gdi_interop;
+static IDWriteRenderingParams *rendering_params;
+
+/* Function prototypes.  */
+void w32_initialize_direct_write (void);
+bool w32_use_direct_write (struct w32font_info *w32font);
+void w32_dwrite_draw (HDC hdc, int x, int y, unsigned *glyphs, int len,
+		      COLORREF color, struct font *font );
+void 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);
+
+/* This two functions are on w32uninscribe.c  */
+void *w32_font_get_dwrite_cache (struct font *font, float *font_size);
+void w32_font_set_dwrite_cache (struct font *font, void *cache,
+				float font_size);
+
+static void
+verify_hr (HRESULT hr, const char *msg)
+{
+  if (FAILED (hr))
+    emacs_abort ();
+}
+
+/* Gets a IDWriteFontFace from a struct font (its HFONT). Returns the
+   font size in points.  It may fail to get a DirectWrite font, and face
+   will be NULL on return.  This happens for some fonts like Courier.
+
+   Never call Release on the result, as it is cached for reuse on the
+   struct font.  */
+static float
+get_font_face (struct font *infont, IDWriteFontFace **face)
+{
+  HRESULT hr;
+  LOGFONTW logfont;
+  IDWriteFont *font;
+  float font_size;
+
+  /* Check the cache.  */
+  *face = w32_font_get_dwrite_cache (infont, &font_size);
+  if (*face)
+    return font_size;
+
+  GetObjectW (FONT_HANDLE(infont), sizeof (LOGFONTW), &logfont);
+
+  hr = gdi_interop->lpVtbl->
+    CreateFontFromLOGFONT (gdi_interop, (const LOGFONTW *) &logfont, &font);
+
+  if (FAILED (hr))
+    {
+      *face = NULL;
+      return 0.0;
+    }
+
+  hr = font->lpVtbl->CreateFontFace (font, face);
+  RELEASE_COM (font);
+  verify_hr (hr, "Failed to create DWriteFontFace");
+  w32_font_set_dwrite_cache (infont, *face, abs(logfont.lfHeight));
+
+  return abs(logfont.lfHeight);
+}
+
+void
+w32_dwrite_free_cached_face(void *cache)
+{
+  if (cache)
+    RELEASE_COM ((IDWriteFontFace *) cache);
+}
+
+static float
+convert_metrics_sz( int sz, float font_size, int units_per_em )
+{
+  return (float)sz * font_size / units_per_em;
+}
+
+
+/* Does not fill in the ascent and descent fields of metrics.  */
+static void
+text_extents_internal (IDWriteFontFace *dwrite_font_face,
+		       float font_size, const unsigned *code,
+		       int nglyphs, struct font_metrics *metrics)
+{
+  HRESULT hr;
+
+  DWRITE_FONT_METRICS dwrite_font_metrics;
+  dwrite_font_face->lpVtbl->
+    GetMetrics (dwrite_font_face, &dwrite_font_metrics);
+
+  UINT16 *indices = alloca (nglyphs * sizeof (UINT16));
+  for (int i = 0; i < nglyphs; i++)
+    indices[i] = code[i];
+
+  DWRITE_GLYPH_METRICS* gmetrics =
+    alloca (nglyphs * sizeof (DWRITE_GLYPH_METRICS));
+
+  hr = dwrite_font_face->lpVtbl->
+    GetGdiCompatibleGlyphMetrics (dwrite_font_face,
+				  font_size,
+				  1.0,
+				  NULL,
+				  TRUE,
+				  indices,
+				  nglyphs,
+				  gmetrics,
+				  false);
+  verify_hr (hr, "Failed to GetGdiCompatibleGlyphMetrics");
+
+  float width = 0;
+  int du_per_em = dwrite_font_metrics.designUnitsPerEm;
+
+  for (int i = 0; i < nglyphs; i++)
+    {
+      float advance =
+	convert_metrics_sz (gmetrics[i].advanceWidth, font_size, du_per_em);
+
+      width += advance;
+
+      float lbearing =
+	round (convert_metrics_sz (gmetrics[i].leftSideBearing, font_size,
+				   du_per_em));
+      float rbearing =
+	round (advance -
+	       convert_metrics_sz (gmetrics[i].rightSideBearing,
+				   font_size, du_per_em));
+      if (i == 0)
+	{
+	  metrics->lbearing = lbearing;
+	  metrics->rbearing = rbearing;
+	}
+      if (metrics->lbearing > lbearing)
+	metrics->lbearing = lbearing;
+      if (metrics->rbearing < rbearing)
+	metrics->rbearing = rbearing;
+    }
+  metrics->width = round(width);
+}
+
+unsigned
+w32_dwrite_encode_char (struct font *font, int c)
+{
+  HRESULT hr;
+  IDWriteFontFace *dwrite_font_face;
+  UINT16 index;
+
+  get_font_face (font, &dwrite_font_face);
+  hr = dwrite_font_face->lpVtbl->
+    GetGlyphIndices (dwrite_font_face, &c, 1, &index);
+  verify_hr (hr, "Failed to GetGlyphIndices");
+
+  if (index == 0)
+    return FONT_INVALID_CODE;
+
+  return index;
+}
+
+void
+w32_dwrite_text_extents (struct font *font, const unsigned *code, int nglyphs,
+			 struct font_metrics *metrics)
+{
+  IDWriteFontFace *dwrite_font_face;
+
+  float font_size = get_font_face (font, &dwrite_font_face);
+
+  if (dwrite_font_face == NULL)
+    {
+      metrics->width = 0;
+      metrics->lbearing = 0;
+      metrics->rbearing = 0;
+      return;
+    }
+
+  text_extents_internal (dwrite_font_face, font_size, code, nglyphs, metrics);
+
+  metrics->ascent = font->ascent;
+  metrics->descent = font->descent;
+}
+
+/* Never call Release on the value returned by this function, as it is
+   reused.  */
+static IDWriteBitmapRenderTarget *
+get_bitmap_render_target (HDC hdc, int width, int height)
+{
+  HRESULT hr;
+  static IDWriteBitmapRenderTarget *brt = NULL;
+  static SIZE size = {0, 0};
+
+  if (brt)
+    {
+      /* Check if we need to make a bigger one.  */
+      if (width <= size.cx && height <= size.cy)
+	return brt;
+      RELEASE_COM (brt);
+    }
+
+  if (width > size.cx)
+    size.cx = width;
+  if (height > size.cy)
+    size.cy = height;
+
+  hr = gdi_interop->lpVtbl->
+    CreateBitmapRenderTarget (gdi_interop, hdc, size.cx, size.cy, &brt);
+  verify_hr (hr, "Failed to create DWriteBitmapRenderTarget");
+
+  /* We handle high dpi displays by incresing font size, so override
+     PixelsPerDip.  */
+  brt->lpVtbl->SetPixelsPerDip (brt, 1.0);
+
+  /* The SetTextAntialiasMode method is only available in
+     IDWriteBitmapRenderTarget1.  */
+  IDWriteBitmapRenderTarget1 *brt1;
+  hr = brt->lpVtbl->
+    QueryInterface (brt, &IID_IDWriteBitmapRenderTarget1, (void **) &brt1);
+  if (SUCCEEDED (hr))
+    {
+      brt1->lpVtbl->
+	SetTextAntialiasMode (brt1, ANTIALIAS_MODE);
+      RELEASE_COM (brt1);
+    }
+
+  return brt;
+}
+
+void
+w32_initialize_direct_write (void)
+{
+  direct_write_available = false;
+  HMODULE direct_write = LoadLibrary ("dwrite.dll");
+  if (!direct_write)
+    return;
+
+  /* This is only used here, no need to define it globally.  */
+  typedef HRESULT (WINAPI *CreateFactory) (DWRITE_FACTORY_TYPE f, REFIID r, IUnknown** u);
+
+  CreateFactory create_factory
+    = (CreateFactory) get_proc_addr (direct_write, "DWriteCreateFactory");
+
+  if (!create_factory)
+    {
+      FreeLibrary (direct_write);
+      return;
+    }
+
+  HRESULT hr = create_factory (DWRITE_FACTORY_TYPE_SHARED,
+			       &IID_IDWriteFactory,
+			       (IUnknown **) &dwrite_factory);
+  if (FAILED (hr))
+    {
+      FreeLibrary (direct_write);
+      return;
+    }
+
+  hr = dwrite_factory->lpVtbl->
+    QueryInterface (dwrite_factory, &IID_IDWriteFactory2,
+		    (void **) &dwrite_factory2);
+
+  if (FAILED (hr))
+    {
+      RELEASE_COM (dwrite_factory);
+      FreeLibrary (direct_write);
+      return;
+    }
+
+  hr = dwrite_factory->lpVtbl->
+    GetGdiInterop (dwrite_factory, &gdi_interop);
+  if (FAILED (hr))
+    {
+      RELEASE_COM (dwrite_factory);
+      RELEASE_COM (dwrite_factory2);
+      FreeLibrary (direct_write);
+      return;
+    }
+
+  IDWriteRenderingParams *def;
+
+  hr = dwrite_factory->lpVtbl->
+    CreateRenderingParams (dwrite_factory, &def);
+  if (FAILED (hr))
+    {
+      RELEASE_COM (dwrite_factory);
+      RELEASE_COM (dwrite_factory2);
+      RELEASE_COM (gdi_interop);
+      FreeLibrary (direct_write);
+      return;
+    }
+
+  /* range: [0.0, 1.0]  */
+  float enhanced_contrast = def->lpVtbl->GetEnhancedContrast(def);
+  /* range: [0.0, 1.0]  */
+  float clear_type_level = def->lpVtbl->GetClearTypeLevel(def);
+  /* range: (0.0, 256.0] */
+  float gamma = 1.4; /* def->lpVtbl->GetGamma(def); */
+
+  hr = dwrite_factory->lpVtbl->
+    CreateCustomRenderingParams (dwrite_factory,
+				 gamma,
+				 enhanced_contrast,
+				 clear_type_level,
+				 def->lpVtbl->GetPixelGeometry(def),
+				 RENDERING_MODE,
+				 &rendering_params);
+  RELEASE_COM (def);
+
+  if (FAILED (hr))
+    {
+      RELEASE_COM (dwrite_factory);
+      RELEASE_COM (dwrite_factory2);
+      RELEASE_COM (gdi_interop);
+      FreeLibrary (direct_write);
+      return;
+    }
+
+  direct_write_available = true;
+
+  DEFVAR_BOOL ("w32-inhibit-direct-write", w32_inhibit_direct_write,
+	       doc: /* If t, don't use DirectWrite.  */);
+  w32_inhibit_direct_write = false;
+}
+
+void w32_dwrite_draw (HDC hdc, int x, int y, unsigned *glyphs, int len,
+		      COLORREF color, struct font *font)
+{
+  HRESULT hr;
+  IDWriteFontFace *dwrite_font_face;
+
+  /* What we get as y is the baseline position.  */
+  y -= font->ascent;
+
+  float font_size = get_font_face (font, &dwrite_font_face);
+  if (dwrite_font_face == NULL)
+    return;
+
+  struct font_metrics metrics;
+  text_extents_internal (dwrite_font_face, font_size, glyphs, len, &metrics);
+
+  int bitmap_width = metrics.width + metrics.rbearing;
+  int bitmap_height = font->ascent + font->descent;
+
+  /* We never Release this, get_bitmap_render_target reuses it.  */
+  IDWriteBitmapRenderTarget *bitmap_render_target =
+    get_bitmap_render_target (hdc, bitmap_width, bitmap_height);
+
+  /* This DC can't be released.  */
+  HDC text_dc = bitmap_render_target->lpVtbl->
+    GetMemoryDC (bitmap_render_target);
+
+  /* Copy the background pixel to the render target bitmap.  */
+  BitBlt (text_dc, 0, 0, bitmap_width, bitmap_height, hdc, x, y, SRCCOPY);
+
+
+  UINT16 *indices = alloca (len * sizeof (UINT16));
+
+  for (int i = 0; i < len; i++)
+    indices[i] = glyphs[i];
+
+  FLOAT *advances = alloca (len * sizeof (FLOAT));
+
+  for (int i = 0; i < len; i++)
+    {
+      text_extents_internal (dwrite_font_face, font_size, glyphs + i, 1,
+			     &metrics);
+      advances[i] = metrics.width;
+    }
+
+  DWRITE_GLYPH_RUN glyph_run;
+  glyph_run.fontFace = dwrite_font_face;
+  glyph_run.fontEmSize = font_size;
+  glyph_run.glyphIndices = indices;
+  glyph_run.glyphCount = len;
+  glyph_run.isSideways = false;
+  glyph_run.bidiLevel = 0;
+  glyph_run.glyphOffsets = NULL;
+  glyph_run.glyphAdvances = advances;
+
+  IDWriteColorGlyphRunEnumerator *layers;
+  /* This call will tell us if we hace to handle any color glyph.  */
+  hr = dwrite_factory2->lpVtbl->
+    TranslateColorGlyphRun (dwrite_factory2,
+			    0, font->ascent,
+			    &glyph_run,
+			    NULL,
+			    MEASURING_MODE,
+			    NULL,
+			    0,
+			    &layers);
+
+  /* No color. Just draw the GlyphRun.  */
+  if (hr == DWRITE_E_NOCOLOR)
+    {
+      bitmap_render_target->lpVtbl->
+	DrawGlyphRun (bitmap_render_target,
+		      0, font->ascent,
+		      MEASURING_MODE,
+		      &glyph_run,
+		      rendering_params,
+		      color,
+		      NULL);
+    }
+  else
+    {
+      /* If there were color glyphs, layers contains a containts a list
+	 of GlyphRun with a color and a position for each.  We draw them
+	 individually.  */
+      verify_hr (hr, "Failed at TranslateColorGlyphRun");
+      for (;;) {
+	HRESULT hr;
+	BOOL more_layers;
+	const DWRITE_COLOR_GLYPH_RUN *layer;
+
+	hr = layers->lpVtbl->MoveNext (layers, &more_layers);
+	verify_hr (hr, "Failed at MoveNext");
+	if (!more_layers)
+	  break;
+	hr = layers->lpVtbl->GetCurrentRun (layers, &layer);
+	verify_hr (hr, "Failed at GetCurrentRun");
+	bitmap_render_target->lpVtbl->
+	  DrawGlyphRun (bitmap_render_target,
+			layer->baselineOriginX, layer->baselineOriginY,
+			MEASURING_MODE,
+			&layer->glyphRun,
+			rendering_params,
+			RGB (layer->runColor.r * 255,
+			     layer->runColor.g * 255,
+			     layer->runColor.b * 255),
+			NULL);
+      }
+      RELEASE_COM (layers);
+    }
+
+  /* Finally, copy the rendered text back to the original DC.  */
+  BitBlt (hdc, x, y, bitmap_width, bitmap_height, text_dc, 0, 0, SRCCOPY);
+}
+
+/* Returns true if DirectWrite is to be used:
+   - Is is available.
+   - The font is handled by harfbuzz
+   - w32-inhibit-direct-write is false
+ */
+bool
+w32_use_direct_write (struct w32font_info *w32font)
+{
+#ifdef HAVE_HARFBUZZ
+  return direct_write_available
+    && w32font->font.driver == &harfbuzz_font_driver
+    && !w32_inhibit_direct_write;
+#else
+  return false;
+#endif
+}
diff --git a/src/w32font.c b/src/w32font.c
index efb42d80336..16aa9308584 100644
--- a/src/w32font.c
+++ b/src/w32font.c
@@ -55,6 +55,13 @@ #define VIETNAMESE_CHARSET 163
 #define JOHAB_CHARSET 130
 #endif
 
+/* Function prototypes from w32write.c  */
+bool w32_use_direct_write (struct w32font_info *w32font);
+void w32_dwrite_draw (HDC hdc, int x, int y, unsigned *glyphs, int len,
+		  COLORREF color, struct font *font );
+void w32_dwrite_text_extents (struct font *font, const unsigned *code,
+			  int nglyphs, struct font_metrics *metrics);
+
 static void fill_in_logfont (struct frame *, LOGFONT *, Lisp_Object);
 
 static BYTE w32_antialias_type (Lisp_Object);
@@ -452,6 +459,12 @@ w32font_text_extents (struct font *font, const unsigned *code,
 
   memset (metrics, 0, sizeof (struct font_metrics));
 
+  if (w32_use_direct_write (w32_font))
+    {
+      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 +719,36 @@ 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);
+	  }
+	else
+	  {
+	    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 );
+	}
+      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);
+	}
     }
 
   /* Restore clip region.  */
diff --git a/src/w32uniscribe.c b/src/w32uniscribe.c
index b77bf56b8cf..af05d050936 100644
--- a/src/w32uniscribe.c
+++ b/src/w32uniscribe.c
@@ -44,6 +44,15 @@ #define _WIN32_WINNT 0x0600
 #include "pdumper.h"
 #include "w32common.h"
 
+/* Function prototypes from w32dwrite.c  */
+bool w32_use_direct_write (struct w32font_info *w32font);
+unsigned w32_dwrite_encode_char (struct font *font, int c);
+void w32_dwrite_free_cached_face (void *cache);
+
+/* Function prototypes from this file  */
+void *w32_font_get_dwrite_cache (struct font *font, float *font_size);
+void w32_font_set_dwrite_cache (struct font *font, void *cache, float font_size);
+
 /* Extension of w32font_info used by Uniscribe and HarfBuzz backends.  */
 struct uniscribe_font_info
 {
@@ -54,8 +63,25 @@ #define _WIN32_WINNT 0x0600
   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.  */
+  void *dwrite_cache;
+  float dwrite_font_size;
 };
 
+void *w32_font_get_dwrite_cache (struct font *font, float *font_size)
+{
+  *font_size = ((struct uniscribe_font_info *) font)->dwrite_font_size;
+  return ((struct uniscribe_font_info *) font)->dwrite_cache;
+}
+
+void w32_font_set_dwrite_cache (struct font *font, void *cache, float font_size)
+{
+  ((struct uniscribe_font_info *) font)->dwrite_font_size = font_size;
+  ((struct uniscribe_font_info *) font)->dwrite_cache = cache;
+}
+
 int uniscribe_available = 0;
 
 /* EnumFontFamiliesEx callback.  */
@@ -200,6 +226,7 @@ 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 and HarfBuzz backends use glyph indices.  */
   uniscribe_font->w32_font.glyph_idx = ETO_GLYPH_INDEX;
@@ -221,6 +248,7 @@ 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 +1400,12 @@ 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))
+    {
+      return w32_dwrite_encode_char(font, c);
+    }
+
   hb_font_t *hb_font = uniscribe_font->cache;
 
   /* First time we use this font with HarfBuzz, create the hb_font_t
@@ -1531,6 +1565,8 @@ load_harfbuzz_funcs (HMODULE library)
 }
 #endif	/* HAVE_HARFBUZZ */
 
+void w32_initialize_direct_write (void);
+
 static void
 syms_of_w32uniscribe_for_pdumper (void)
 {
@@ -1624,5 +1660,8 @@ 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 */
 }
-- 
2.35.1.windows.2