Windows QPA: Add helper function to obtain DPI-dependent metrics on Windows 10

Use newly introduced SystemParametersInfoForDpi() API with some convenience
overloads.

Task-number: QTBUG-4362
Change-Id: I4c41c700007bf7cc4fd5868356e3145c136704c0
Reviewed-by: Oliver Wolff <oliver.wolff@qt.io>

3 files changed, 55 insertions, 3 deletions

diff --git a/src/plugins/platforms/windows/qwindowscontext.cpp b/src/plugins/platforms/windows/qwindowscontext.cpp
index 4959ed952d..1f80ac5872 100644
--- a/src/plugins/platforms/windows/qwindowscontext.cpp
+++ b/src/plugins/platforms/windows/qwindowscontext.cpp
@@ -213,6 +213,7 @@ void QWindowsUser32DLL::init()
         enableNonClientDpiScaling = (EnableNonClientDpiScaling)library.resolve("EnableNonClientDpiScaling");
         getWindowDpiAwarenessContext = (GetWindowDpiAwarenessContext)library.resolve("GetWindowDpiAwarenessContext");
         getAwarenessFromDpiAwarenessContext = (GetAwarenessFromDpiAwarenessContext)library.resolve("GetAwarenessFromDpiAwarenessContext");
+        systemParametersInfoForDpi = (SystemParametersInfoForDpi)library.resolve("SystemParametersInfoForDpi");
     }
 }
 
@@ -916,6 +917,45 @@ QByteArray QWindowsContext::comErrorString(HRESULT hr)
     return result;
 }
 
+bool QWindowsContext::systemParametersInfo(unsigned action, unsigned param, void *out,
+                                           unsigned dpi)
+{
+    const BOOL result = QWindowsContext::user32dll.systemParametersInfoForDpi != nullptr && dpi != 0
+        ? QWindowsContext::user32dll.systemParametersInfoForDpi(action, param, out, 0, dpi)
+        : SystemParametersInfo(action, param, out, 0);
+    return result == TRUE;
+}
+
+bool QWindowsContext::systemParametersInfoForScreen(unsigned action, unsigned param, void *out,
+                                                    const QPlatformScreen *screen)
+{
+    return systemParametersInfo(action, param, out, screen ? screen->logicalDpi().first : 0);
+}
+
+bool QWindowsContext::systemParametersInfoForWindow(unsigned action, unsigned param, void *out,
+                                                    const QPlatformWindow *win)
+{
+    return systemParametersInfoForScreen(action, param, out, win ? win->screen() : nullptr);
+}
+
+bool QWindowsContext::nonClientMetrics(NONCLIENTMETRICS *ncm, unsigned dpi)
+{
+    memset(ncm, 0, sizeof(NONCLIENTMETRICS));
+    ncm->cbSize = sizeof(NONCLIENTMETRICS);
+    return systemParametersInfo(SPI_GETNONCLIENTMETRICS, ncm->cbSize, ncm, dpi);
+}
+
+bool QWindowsContext::nonClientMetricsForScreen(NONCLIENTMETRICS *ncm,
+                                                const QPlatformScreen *screen)
+{
+    return nonClientMetrics(ncm, screen ? screen->logicalDpi().first : 0);
+}
+
+bool QWindowsContext::nonClientMetricsForWindow(NONCLIENTMETRICS *ncm, const QPlatformWindow *win)
+{
+    return nonClientMetricsForScreen(ncm, win ? win->screen() : nullptr);
+}
+
 static inline QWindowsInputContext *windowsInputContext()
 {
     return qobject_cast<QWindowsInputContext *>(QWindowsIntegration::instance()->inputContext());
diff --git a/src/plugins/platforms/windows/qwindowscontext.h b/src/plugins/platforms/windows/qwindowscontext.h
index 19e9c26130..fd6c72668c 100644
--- a/src/plugins/platforms/windows/qwindowscontext.h
+++ b/src/plugins/platforms/windows/qwindowscontext.h
@@ -70,6 +70,7 @@ Q_DECLARE_LOGGING_CATEGORY(lcQpaTrayIcon)
 
 class QWindow;
 class QPlatformScreen;
+class QPlatformWindow;
 class QWindowsMenuBar;
 class QWindowsScreenManager;
 class QWindowsTabletSupport;
@@ -104,6 +105,7 @@ struct QWindowsUser32DLL
     typedef BOOL (WINAPI *EnableNonClientDpiScaling)(HWND);
     typedef int  (WINAPI *GetWindowDpiAwarenessContext)(HWND);
     typedef int  (WINAPI *GetAwarenessFromDpiAwarenessContext)(int);
+    typedef BOOL (WINAPI *SystemParametersInfoForDpi)(UINT, UINT, PVOID, UINT, UINT);
 
     // Windows pointer functions (Windows 8 or later).
     EnableMouseInPointer enableMouseInPointer = nullptr;
@@ -132,6 +134,7 @@ struct QWindowsUser32DLL
     EnableNonClientDpiScaling enableNonClientDpiScaling = nullptr;
     GetWindowDpiAwarenessContext getWindowDpiAwarenessContext = nullptr;
     GetAwarenessFromDpiAwarenessContext getAwarenessFromDpiAwarenessContext = nullptr;
+    SystemParametersInfoForDpi systemParametersInfoForDpi = nullptr;
 };
 
 // Shell scaling library (Windows 8.1 onwards)
@@ -237,6 +240,17 @@ public:
     bool asyncExpose() const;
     void setAsyncExpose(bool value);
 
+    static bool systemParametersInfo(unsigned action, unsigned param, void *out, unsigned dpi = 0);
+    static bool systemParametersInfoForScreen(unsigned action, unsigned param, void *out,
+                                              const QPlatformScreen *screen = nullptr);
+    static bool systemParametersInfoForWindow(unsigned action, unsigned param, void *out,
+                                              const QPlatformWindow *win = nullptr);
+    static bool nonClientMetrics(NONCLIENTMETRICS *ncm, unsigned dpi = 0);
+    static bool nonClientMetricsForScreen(NONCLIENTMETRICS *ncm,
+                                          const QPlatformScreen *screen = nullptr);
+    static bool nonClientMetricsForWindow(NONCLIENTMETRICS *ncm,
+                                          const QPlatformWindow *win = nullptr);
+
     static DWORD readAdvancedExplorerSettings(const wchar_t *subKey, DWORD defaultValue);
 
     QTouchDevice *touchDevice() const;
diff --git a/src/plugins/platforms/windows/qwindowstheme.cpp b/src/plugins/platforms/windows/qwindowstheme.cpp
index d01a7b0a8a..4b70e915a8 100644
--- a/src/plugins/platforms/windows/qwindowstheme.cpp
+++ b/src/plugins/platforms/windows/qwindowstheme.cpp
@@ -507,9 +507,7 @@ void QWindowsTheme::refreshFonts()
     if (!QGuiApplication::desktopSettingsAware())
         return;
     NONCLIENTMETRICS ncm;
-    ncm.cbSize = FIELD_OFFSET(NONCLIENTMETRICS, lfMessageFont) + sizeof(LOGFONT);
-    SystemParametersInfo(SPI_GETNONCLIENTMETRICS, ncm.cbSize , &ncm, 0);
-
+    QWindowsContext::nonClientMetrics(&ncm);
     const QFont menuFont = QWindowsFontDatabase::LOGFONT_to_QFont(ncm.lfMenuFont);
     const QFont messageBoxFont = QWindowsFontDatabase::LOGFONT_to_QFont(ncm.lfMessageFont);
     const QFont statusFont = QWindowsFontDatabase::LOGFONT_to_QFont(ncm.lfStatusFont);