make the render process DPI-aware

On Windows, system calls that retrieve screen properties (like
GetSystemMetrics to get the size of a scroll bar button) are dependent
on the DPI awareness setting of the calling process.
The render process must use the same DPI awareness setting as the
browser process. Retrieve the DPI awareness of the parent process in
the render process and set it accordingly.

Task-number: QTBUG-48380
Change-Id: Ic17d29d0f584e3cf230ac6ea2b08e3aa0d87ccdd
Reviewed-by: Allan Sandfeld Jensen <[email protected]>

Author: jobor

src/process/main.cpp

@@ -146,8 +146,16 @@ int stat64_proxy(const char *path, struct stat64 *buf)
 #endif
 #endif // defined(OS_LINUX)
 
+#ifdef Q_OS_WIN
+void initDpiAwareness();
+#endif // defined(Q_OS_WIN)
+
 int main(int argc, const char **argv)
 {
+#ifdef Q_OS_WIN
+    initDpiAwareness();
+#endif
+
     // QCoreApplication needs a non-const pointer, while the
     // ContentMain in Chromium needs the pointer to be const.
     QCoreApplication qtApplication(argc, const_cast<char**>(argv));

src/process/process.pro

@@ -40,6 +40,11 @@ INCLUDEPATH += ../core
 
 SOURCES = main.cpp
 
+win32 {
+    SOURCES += \
+        support_win.cpp
+}
+
 contains(QT_CONFIG, qt_framework) {
     target.path = $$[QT_INSTALL_LIBS]/QtWebEngineCore.framework/Versions/5/Helpers
 } else {

src/process/support_win.cpp

@@ -0,0 +1,155 @@
+/****************************************************************************
+**
+** Copyright (C) 2015 The Qt Company Ltd.
+** Contact: http://www.qt.io/licensing/
+**
+** This file is part of the QtWebEngine module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see http://www.qt.io/terms-conditions. For further
+** information use the contact form at http://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.LGPLv3 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.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 later as published by the Free
+** Software Foundation and appearing in the file LICENSE.GPL included in
+** the packaging of this file. Please review the following information to
+** ensure the GNU General Public License version 2.0 requirements will be
+** met: http://www.gnu.org/licenses/gpl-2.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include <qlibrary.h>
+#include <qsysinfo.h>
+#include <qt_windows.h>
+#include <Tlhelp32.h>
+
+class User32DLL {
+public:
+    User32DLL()
+        : setProcessDPIAware(0)
+    {
+        library.setFileName(QStringLiteral("User32"));
+        if (!library.load())
+            return;
+        setProcessDPIAware = (SetProcessDPIAware)library.resolve("SetProcessDPIAware");
+    }
+
+    bool isValid() const
+    {
+        return setProcessDPIAware;
+    }
+
+    typedef BOOL (WINAPI *SetProcessDPIAware)();
+
+    // Windows Vista onwards
+    SetProcessDPIAware setProcessDPIAware;
+
+private:
+    QLibrary library;
+};
+
+// This must match PROCESS_DPI_AWARENESS in ShellScalingApi.h
+enum DpiAwareness {
+    PROCESS_PER_UNAWARE = 0,
+    PROCESS_PER_SYSTEM_DPI_AWARE = 1,
+    PROCESS_PER_MONITOR_DPI_AWARE = 2
+};
+
+// Shell scaling library (Windows 8.1 onwards)
+class ShcoreDLL {
+public:
+    ShcoreDLL()
+        : getProcessDpiAwareness(0), setProcessDpiAwareness(0)
+    {
+        if (QSysInfo::windowsVersion() < QSysInfo::WV_WINDOWS8_1)
+            return;
+        library.setFileName(QStringLiteral("SHCore"));
+        if (!library.load())
+            return;
+        getProcessDpiAwareness = (GetProcessDpiAwareness)library.resolve("GetProcessDpiAwareness");
+        setProcessDpiAwareness = (SetProcessDpiAwareness)library.resolve("SetProcessDpiAwareness");
+    }
+
+    bool isValid() const
+    {
+        return getProcessDpiAwareness && setProcessDpiAwareness;
+    }
+
+    typedef HRESULT (WINAPI *GetProcessDpiAwareness)(HANDLE, DpiAwareness *);
+    typedef HRESULT (WINAPI *SetProcessDpiAwareness)(DpiAwareness);
+
+    GetProcessDpiAwareness getProcessDpiAwareness;
+    SetProcessDpiAwareness setProcessDpiAwareness;
+
+private:
+    QLibrary library;
+};
+
+
+static DWORD getParentProcessId()
+{
+    HANDLE hSnapshot = CreateToolhelp32Snapshot(TH32CS_SNAPPROCESS, 0);
+    if (hSnapshot == INVALID_HANDLE_VALUE) {
+        qErrnoWarning(GetLastError(), "CreateToolhelp32Snapshot failed.");
+        return NULL;
+    }
+
+    PROCESSENTRY32 pe = {0};
+    pe.dwSize = sizeof(PROCESSENTRY32);
+
+    if (!Process32First(hSnapshot, &pe)) {
+        qWarning("Cannot retrieve parent process handle.");
+        return NULL;
+    }
+
+    DWORD parentPid = NULL;
+    const DWORD pid = GetCurrentProcessId();
+    do {
+        if (pe.th32ProcessID == pid) {
+            parentPid = pe.th32ParentProcessID;
+            break;
+        }
+    } while (Process32Next(hSnapshot, &pe));
+    CloseHandle(hSnapshot);
+    return parentPid;
+}
+
+void initDpiAwareness()
+{
+    ShcoreDLL shcore;
+    if (shcore.isValid()) {
+        DpiAwareness dpiAwareness = PROCESS_PER_MONITOR_DPI_AWARE;
+        const DWORD pid = getParentProcessId();
+        if (pid) {
+            HANDLE hProcess = OpenProcess(PROCESS_QUERY_INFORMATION, FALSE, pid);
+            DpiAwareness parentDpiAwareness;
+            HRESULT hr = shcore.getProcessDpiAwareness(hProcess, &parentDpiAwareness);
+            CloseHandle(hProcess);
+            if (hr == S_OK)
+                dpiAwareness = parentDpiAwareness;
+        }
+        if (shcore.setProcessDpiAwareness(dpiAwareness) != S_OK)
+            qErrnoWarning(GetLastError(), "SetProcessDPIAwareness failed.");
+    } else {
+        // Fallback. Use SetProcessDPIAware unconditionally.
+        User32DLL user32;
+        if (user32.isValid())
+            user32.setProcessDPIAware();
+    }
+}