Add wxWindow::GetDPI()

This is simpler to use than wxDisplay(window).GetPPI() which was used
instead of it so far in all ports and can be implemented more
efficiently for wxMSW.

Remove wxGetWinTLW, GetDPI already tries to get the top window.

include/wx/msw/window.h

@@ -99,6 +99,8 @@ public:
 
     virtual bool Reparent(wxWindowBase *newParent) wxOVERRIDE;
 
+    virtual wxSize GetDPI() const wxOVERRIDE;
+
     virtual void WarpPointer(int x, int y) wxOVERRIDE;
     virtual bool EnableTouchEvents(int eventsMask) wxOVERRIDE;
 

include/wx/window.h

@@ -949,14 +949,16 @@ public:
     // translation between different units
     // -----------------------------------
 
+        // Get the DPI used by the given window or wxSize(0, 0) if unknown.
+    virtual wxSize GetDPI() const;
+
         // DPI-independent pixels, or DIPs, are pixel values for the standard
         // 96 DPI display, they are scaled to take the current resolution into
         // account (i.e. multiplied by the same factor as returned by
         // GetContentScaleFactor()) if necessary for the current platform.
         //
-        // Currently the conversion factor is the same for all windows but this
-        // will change with the monitor-specific resolution support in the
-        // future, so prefer using the non-static member functions.
+        // To support monitor-specific resolutions, prefer using the non-static
+        // member functions or use a valid (non-null) window pointer.
         //
         // Similarly, currently in practice the factor is the same in both
         // horizontal and vertical directions, but this could, in principle,

interface/wx/window.h

@@ -2036,6 +2036,20 @@ public:
     */
     virtual wxVisualAttributes GetDefaultAttributes() const;
 
+    /**
+        Return the DPI of the display used by this window.
+
+        The returned value can be different for different windows on systems
+        with support for per-monitor DPI values, such as Microsoft Windows 10.
+
+        If the DPI is not available, returns @c wxSize(0,0) object.
+
+        @see wxDisplay::GetPPI()
+
+        @since 3.1.3
+     */
+    virtual wxSize GetDPI() const;
+
     /**
         Returns the font for this window.
 

src/common/wincmn.cpp

@@ -74,6 +74,7 @@
     #include "wx/sysopt.h"
 #endif
 
+#include "wx/display.h"
 #include "wx/platinfo.h"
 #include "wx/recguard.h"
 #include "wx/private/window.h"
@@ -2855,6 +2856,11 @@ void wxWindowBase::OnInternalIdle()
 // DPI-independent pixels and dialog units translations
 // ----------------------------------------------------------------------------
 
+wxSize wxWindowBase::GetDPI() const
+{
+    return wxDisplay(static_cast<const wxWindow*>(this)).GetPPI();
+}
+
 #ifndef wxHAVE_DPI_INDEPENDENT_PIXELS
 
 /* static */

src/msw/window.cpp

@@ -4719,23 +4719,28 @@ wxWindowMSW::MSWOnMeasureItem(int id, WXMEASUREITEMSTRUCT *itemStruct)
 namespace
 {
 
-static inline const wxTopLevelWindow* wxGetWinTLW(const wxWindow* win)
+static wxSize GetWindowDPI(HWND hwnd)
 {
-    if ( win )
+#if wxUSE_DYNLIB_CLASS
+    typedef UINT (WINAPI *GetDpiForWindow_t)(HWND hwnd);
+    static GetDpiForWindow_t s_pfnGetDpiForWindow = NULL;
+    static bool s_initDone = false;
+
+    if ( !s_initDone )
     {
-        const wxWindow* tlwWin = wxGetTopLevelParent(const_cast<wxWindow*>(win));
-        return wxDynamicCast(tlwWin, wxTopLevelWindow);
-    }
-    else if ( wxTheApp )
-    {
-        wxWindow* window = wxTheApp->GetTopWindow();
-        if ( window )
-        {
-            return wxDynamicCast(wxGetTopLevelParent(window), wxTopLevelWindow);
-        }
+        wxLoadedDLL dllUser32("user32.dll");
+        wxDL_INIT_FUNC(s_pfn, GetDpiForWindow, dllUser32);
+        s_initDone = true;
     }
 
-    return NULL;
+    if ( s_pfnGetDpiForWindow )
+    {
+        const int dpi = static_cast<int>(s_pfnGetDpiForWindow(hwnd));
+        return wxSize(dpi, dpi);
+    }
+#endif // wxUSE_DYNLIB_CLASS
+
+    return wxSize();
 }
 
 }
@@ -4744,9 +4749,9 @@ static inline const wxTopLevelWindow* wxGetWinTLW(const wxWindow* win)
 int wxGetSystemMetrics(int nIndex, const wxWindow* win)
 {
 #if wxUSE_DYNLIB_CLASS
-    const wxTopLevelWindow* tlw = wxGetWinTLW(win);
+    const wxWindow* window = (!win && wxTheApp) ? wxTheApp->GetTopWindow() : win;
 
-    if ( tlw )
+    if ( window )
     {
         typedef int (WINAPI * GetSystemMetricsForDpi_t)(int nIndex, UINT dpi);
         static GetSystemMetricsForDpi_t s_pfnGetSystemMetricsForDpi = NULL;
@@ -4761,8 +4766,7 @@ int wxGetSystemMetrics(int nIndex, const wxWindow* win)
 
         if ( s_pfnGetSystemMetricsForDpi )
         {
-            WindowHDC hdc(tlw->GetHWND());
-            const int dpi = ::GetDeviceCaps(hdc, LOGPIXELSY);
+            const int dpi = window->GetDPI().y;
             return s_pfnGetSystemMetricsForDpi(nIndex, (UINT)dpi);
         }
     }
@@ -4777,9 +4781,9 @@ int wxGetSystemMetrics(int nIndex, const wxWindow* win)
 bool wxSystemParametersInfo(UINT uiAction, UINT uiParam, PVOID pvParam, UINT fWinIni, const wxWindow* win)
 {
 #if wxUSE_DYNLIB_CLASS
-    const wxTopLevelWindow* tlw = wxGetWinTLW(win);
+    const wxWindow* window = (!win && wxTheApp) ? wxTheApp->GetTopWindow() : win;
 
-    if ( tlw )
+    if ( window )
     {
         typedef int (WINAPI * SystemParametersInfoForDpi_t)(UINT uiAction, UINT uiParam, PVOID pvParam, UINT fWinIni, UINT dpi);
         static SystemParametersInfoForDpi_t s_pfnSystemParametersInfoForDpi = NULL;
@@ -4794,8 +4798,7 @@ bool wxSystemParametersInfo(UINT uiAction, UINT uiParam, PVOID pvParam, UINT fWi
 
         if ( s_pfnSystemParametersInfoForDpi )
         {
-            WindowHDC hdc(tlw->GetHWND());
-            const int dpi = ::GetDeviceCaps(hdc, LOGPIXELSY);
+            const int dpi = window->GetDPI().y;
             if ( s_pfnSystemParametersInfoForDpi(uiAction, uiParam, pvParam, fWinIni, (UINT)dpi) == TRUE )
             {
                 return true;
@@ -4809,6 +4812,31 @@ bool wxSystemParametersInfo(UINT uiAction, UINT uiParam, PVOID pvParam, UINT fWi
     return ::SystemParametersInfo(uiAction, uiParam, pvParam, fWinIni) == TRUE;
 }
 
+wxSize wxWindowMSW::GetDPI() const
+{
+    HWND hwnd = GetHwnd();
+
+    if ( hwnd == NULL )
+    {
+        const wxWindow* topWin = wxGetTopLevelParent(const_cast<wxWindow*>(this));
+        if ( topWin )
+        {
+            hwnd = GetHwndOf(topWin);
+        }
+    }
+
+    wxSize dpi = GetWindowDPI(hwnd);
+
+    if ( !dpi.x || !dpi.y )
+    {
+        WindowHDC hdc(GetHwnd());
+        dpi.x = ::GetDeviceCaps(hdc, LOGPIXELSX);
+        dpi.y = ::GetDeviceCaps(hdc, LOGPIXELSY);
+    }
+
+    return dpi;
+}
+
 // ---------------------------------------------------------------------------
 // colours and palettes
 // ---------------------------------------------------------------------------