Windows: simplify registration of QWindowsMime implementations

Register the QWindowsMime implementation instance in the QWindowsMime
constructor, and remove it again in the destructor.

Provide a convenience static method to register a mime type.

This makes it a lot easier to use the type, without having to use native
interfaces.

Since this requires adding a qwindowsmime.cpp file, move the (so far
internal) documentation there.

Task-number: QTBUG-93632
Change-Id: I3b5e45be6255bd11a576127304c4aec9d7364e69
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>

3 files changed, 158 insertions, 2 deletions

diff --git a/src/gui/CMakeLists.txt b/src/gui/CMakeLists.txt
index 85c14f39ab..6278ea45f9 100644
--- a/src/gui/CMakeLists.txt
+++ b/src/gui/CMakeLists.txt
@@ -413,7 +413,7 @@ qt_internal_extend_target(Gui CONDITION WIN32
         image/qpixmap_win.cpp
         kernel/qwindowdefs_win.h
         platform/windows/qwindowsguieventdispatcher.cpp platform/windows/qwindowsguieventdispatcher_p.h
-        platform/windows/qwindowsmime_p.h
+        platform/windows/qwindowsmime_p.h platform/windows/qwindowsmime.cpp
         platform/windows/qwindowsnativeinterface.cpp
         rhi/cs_tdr_p.h
         rhi/qrhid3d11.cpp rhi/qrhid3d11_p.h
diff --git a/src/gui/platform/windows/qwindowsmime.cpp b/src/gui/platform/windows/qwindowsmime.cpp
new file mode 100644
index 0000000000..a60e72dda7
--- /dev/null
+++ b/src/gui/platform/windows/qwindowsmime.cpp
@@ -0,0 +1,153 @@
+// Copyright (C) 2022 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
+
+#include "qwindowsmime_p.h"
+
+#include <QtGui/private/qguiapplication_p.h>
+#include <QtGui/qpa/qplatformintegration.h>
+
+using namespace QNativeInterface::Private;
+
+/*!
+    \class QWindowsMime
+    \brief The QWindowsMime class maps open-standard MIME to Window Clipboard formats.
+    \internal
+
+    Qt's drag-and-drop and clipboard facilities use the MIME standard.
+    On X11, this maps trivially to the Xdnd protocol, but on Windows
+    although some applications use MIME types to describe clipboard
+    formats, others use arbitrary non-standardized naming conventions,
+    or unnamed built-in formats of Windows.
+
+    By instantiating subclasses of QWindowsMime that provide conversions
+    between Windows Clipboard and MIME formats, you can convert
+    proprietary clipboard formats to MIME formats.
+
+    Qt has predefined support for the following Windows Clipboard formats:
+
+    \table
+    \header \li Windows Format \li Equivalent MIME type
+    \row \li \c CF_UNICODETEXT \li \c text/plain
+    \row \li \c CF_TEXT        \li \c text/plain
+    \row \li \c CF_DIB         \li \c{image/xyz}, where \c xyz is
+                                 a \l{QImageWriter::supportedImageFormats()}{Qt image format}
+    \row \li \c CF_HDROP       \li \c text/uri-list
+    \row \li \c CF_INETURL     \li \c text/uri-list
+    \row \li \c CF_HTML        \li \c text/html
+    \endtable
+
+    An example use of this class would be to map the Windows Metafile
+    clipboard format (\c CF_METAFILEPICT) to and from the MIME type
+    \c{image/x-wmf}. This conversion might simply be adding or removing
+    a header, or even just passing on the data. See \l{Drag and Drop}
+    for more information on choosing and definition MIME types.
+
+    You can check if a MIME type is convertible using canConvertFromMime() and
+    can perform conversions with convertToMime() and convertFromMime().
+
+    \sa QWindowsMimeRegistry
+*/
+
+
+/*!
+    \fn bool QWindowsMime::canConvertFromMime(const FORMATETC &formatetc, const QMimeData *mimeData) const
+    \internal
+
+    Returns \c true if the converter can convert from the \a mimeData to
+    the format specified in \a formatetc.
+
+    All subclasses must reimplement this pure virtual function.
+*/
+
+/*!
+    \fn bool QWindowsMime::canConvertToMime(const QString &mimeType, IDataObject *pDataObj) const
+    \internal
+
+    Returns \c true if the converter can convert to the \a mimeType from
+    the available formats in \a pDataObj.
+
+    All subclasses must reimplement this pure virtual function.
+*/
+
+/*!
+    \fn QString QWindowsMime::mimeForFormat(const FORMATETC &formatetc) const
+    \internal
+
+    Returns the mime type that will be created form the format specified
+    in \a formatetc, or an empty string if this converter does not support
+    \a formatetc.
+
+    All subclasses must reimplement this pure virtual function.
+*/
+
+/*!
+    \fn QList<FORMATETC> QWindowsMime::formatsForMime(const QString &mimeType, const QMimeData *mimeData) const
+    \internal
+
+    Returns a QList of FORMATETC structures representing the different windows clipboard
+    formats that can be provided for the \a mimeType from the \a mimeData.
+
+    All subclasses must reimplement this pure virtual function.
+*/
+
+/*!
+    \fn QVariant QWindowsMime::convertToMime(const QString &mimeType, IDataObject *pDataObj,
+                                             QMetaType preferredType) const
+    \internal
+
+    Returns a QVariant containing the converted data for \a mimeType from \a pDataObj.
+    If possible the QVariant should be of the \a preferredType to avoid needless conversions.
+
+    All subclasses must reimplement this pure virtual function.
+*/
+
+/*!
+    \fn bool QWindowsMime::convertFromMime(const FORMATETC &formatetc, const QMimeData *mimeData, STGMEDIUM * pmedium) const
+    \internal
+
+    Convert the \a mimeData to the format specified in \a formatetc.
+    The converted data should then be placed in \a pmedium structure.
+
+    Return true if the conversion was successful.
+
+    All subclasses must reimplement this pure virtual function.
+*/
+
+/*!
+    Constructs a QWindowsMime instance.
+
+    The instance is automatically registered, and will be called to convert data during
+    clipboard or drag'n'drop operations.
+*/
+QWindowsMime::QWindowsMime()
+{
+    auto nativeWindowsApp = dynamic_cast<QWindowsApplication *>(QGuiApplicationPrivate::platformIntegration());
+    Q_ASSERT(nativeWindowsApp);
+    nativeWindowsApp->registerMime(this);
+}
+
+/*!
+    Constructs a QWindowsMime instance.
+
+    The instance is automatically unregistered.
+*/
+QWindowsMime::~QWindowsMime()
+{
+    auto nativeWindowsApp = dynamic_cast<QWindowsApplication *>(QGuiApplicationPrivate::platformIntegration());
+    Q_ASSERT(nativeWindowsApp);
+    nativeWindowsApp->unregisterMime(this);
+}
+
+/*!
+    Registers the MIME type \a mime, and returns an ID number
+    identifying the format on Windows.
+
+    A mime type \c {application/x-qt-windows-mime;value="WindowsType"} will be
+    registered as the clipboard format for \c WindowsType.
+*/
+int QWindowsMime::registerMimeType(const QString &mimeType)
+{
+    auto nativeWindowsApp = dynamic_cast<QWindowsApplication *>(QGuiApplicationPrivate::platformIntegration());
+    Q_ASSERT(nativeWindowsApp);
+    return nativeWindowsApp->registerMimeType(mimeType);
+}
diff --git a/src/gui/platform/windows/qwindowsmime_p.h b/src/gui/platform/windows/qwindowsmime_p.h
index a2fbd38119..f097a618ef 100644
--- a/src/gui/platform/windows/qwindowsmime_p.h
+++ b/src/gui/platform/windows/qwindowsmime_p.h
@@ -30,7 +30,10 @@ namespace QNativeInterface::Private {
 class Q_GUI_EXPORT QWindowsMime
 {
 public:
-    virtual ~QWindowsMime() = default;
+    QWindowsMime();
+    virtual ~QWindowsMime();
+
+    static int registerMimeType(const QString &mimeType);
 
     // for converting from Qt
     virtual bool canConvertFromMime(const FORMATETC &formatetc, const QMimeData *mimeData) const = 0;