Add color font support on Windows

Detect if DirectWrite 2 is available, and support color fonts if possible.
One limitation worth mentioning is that if the color font contains regular,
monochrome glyphs as well, then these will be drawn in black, and not in the
pen color. Fixing this would require some elaborate rewrites in the font
rendering system, since we would have to have two font caches per
color font (one for mono and one for colors), or do some sort of trick where
we make argb(r, g, b, 0) mean subpixel alpha instead, and detect glyphs that
are not correctly premultiplied when blitting to the screen.

Another limitation is that the approach does not work with distance field
rendering. In principle we could support this on Windows, since the
format is vector based, but it would also require substantial work and
it is not possible to support for Apple/Google fonts anyway, so it would
just lead to code which is not cross-platform.

[ChangeLog][Windows] Added support for color fonts (color emojis) when
DirectWrite 2 is available.

Change-Id: I6a608dd5d2aa3a7e762a06830902bddac7c550a5
Reviewed-by: Simon Hausmann <simon.hausmann@theqtcompany.com>

1 files changed, 50 insertions, 0 deletions

diff --git a/config.tests/win/directwrite2/directwrite2.cpp b/config.tests/win/directwrite2/directwrite2.cpp
new file mode 100644
index 0000000000..06becaff70
--- /dev/null
+++ b/config.tests/win/directwrite2/directwrite2.cpp
@@ -0,0 +1,50 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the config.tests of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
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+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include <dwrite_2.h>
+#include <d2d1.h>
+
+int main(int, char**)
+{
+    IUnknown *factory = 0;
+    DWriteCreateFactory(DWRITE_FACTORY_TYPE_SHARED,
+                        __uuidof(IDWriteFactory2),
+                        &factory);
+    return 0;
+}