Support DPI change in sizers

Return the size of DoGetDefaultBorderInPx as float, so no precision is lost
when multiplying it for DoubleBorder and TripleBorder.

Closes #18551.

include/wx/sizer.h

@@ -106,6 +106,11 @@ public:
 
     // default border size used by Border() below
     static int GetDefaultBorder()
+    {
+        return wxRound(GetDefaultBorderFractional());
+    }
+
+    static float GetDefaultBorderFractional()
     {
 #if wxUSE_BORDER_BY_DEFAULT
     #ifdef __WXGTK20__
@@ -145,7 +150,7 @@ public:
     wxSizerFlags& Border(int direction = wxALL)
     {
 #if wxUSE_BORDER_BY_DEFAULT
-        return Border(direction, GetDefaultBorder());
+        return Border(direction, wxRound(GetDefaultBorderFractional()));
 #else
         // no borders by default on limited size screen
         wxUnusedVar(direction);
@@ -157,7 +162,7 @@ public:
     wxSizerFlags& DoubleBorder(int direction = wxALL)
     {
 #if wxUSE_BORDER_BY_DEFAULT
-        return Border(direction, 2*GetDefaultBorder());
+        return Border(direction, wxRound(2 * GetDefaultBorderFractional()));
 #else
         wxUnusedVar(direction);
 
@@ -168,7 +173,7 @@ public:
     wxSizerFlags& TripleBorder(int direction = wxALL)
     {
 #if wxUSE_BORDER_BY_DEFAULT
-        return Border(direction, 3*GetDefaultBorder());
+        return Border(direction, wxRound(3 * GetDefaultBorderFractional()));
 #else
         wxUnusedVar(direction);
 
@@ -179,7 +184,7 @@ public:
     wxSizerFlags& HorzBorder()
     {
 #if wxUSE_BORDER_BY_DEFAULT
-        return Border(wxLEFT | wxRIGHT, GetDefaultBorder());
+        return Border(wxLEFT | wxRIGHT, wxRound(GetDefaultBorderFractional()));
 #else
         return *this;
 #endif
@@ -188,7 +193,7 @@ public:
     wxSizerFlags& DoubleHorzBorder()
     {
 #if wxUSE_BORDER_BY_DEFAULT
-        return Border(wxLEFT | wxRIGHT, 2*GetDefaultBorder());
+        return Border(wxLEFT | wxRIGHT, wxRound(2 * GetDefaultBorderFractional()));
 #else
         return *this;
 #endif
@@ -223,7 +228,7 @@ public:
 
 private:
 #ifdef wxNEEDS_BORDER_IN_PX
-    static int DoGetDefaultBorderInPx();
+    static float DoGetDefaultBorderInPx();
 #endif // wxNEEDS_BORDER_IN_PX
 
     int m_proportion;

interface/wx/sizer.h

@@ -1493,9 +1493,21 @@ public:
         This value is scaled appropriately for the current DPI on the systems
         where physical pixel values are used for the control positions and
         sizes, i.e. not with wxGTK or wxOSX.
+
+        @see GetDefaultBorderFractional()
     */
     static int GetDefaultBorder();
 
+    /**
+        Returns the border used by default, with fractional precision. For
+        example when the border is scaled to a non-integer DPI.
+
+        @see GetDefaultBorder()
+
+        @since 3.1.4
+    */
+    static float GetDefaultBorderFractional();
+
     /**
         Aligns the object to the left, similar for @c Align(wxALIGN_LEFT).
 

src/common/sizer.cpp

@@ -93,7 +93,7 @@ WX_DEFINE_EXPORTED_LIST( wxSizerItemList )
 #ifdef wxNEEDS_BORDER_IN_PX
 
 /* static */
-int wxSizerFlags::DoGetDefaultBorderInPx()
+float wxSizerFlags::DoGetDefaultBorderInPx()
 {
     // Hard code 5px as it's the minimal border size between two controls, see
     // the table at the bottom of
@@ -107,9 +107,12 @@ int wxSizerFlags::DoGetDefaultBorderInPx()
     // as we don't have any associated window -- but, again, without changes
     // in the API, there is nothing we can do about this.
     const wxWindow* const win = wxTheApp ? wxTheApp->GetTopWindow() : NULL;
-    static wxPrivate::DpiDependentValue<int> s_defaultBorderInPx;
+    static wxPrivate::DpiDependentValue<float> s_defaultBorderInPx;
     if ( s_defaultBorderInPx.HasChanged(win) )
-        s_defaultBorderInPx.SetAtNewDPI(wxWindow::FromDIP(5, win));
+    {
+        s_defaultBorderInPx.SetAtNewDPI(
+            (float)(5 * (win ? win->GetContentScaleFactor() : 1)));
+    }
     return s_defaultBorderInPx.Get();
 }
 

src/msw/window.cpp

@@ -4884,6 +4884,37 @@ wxWindowMSW::MSWUpdateOnDPIChange(const wxSize& oldDPI, const wxSize& newDPI)
     // update font if necessary
     MSWUpdateFontOnDPIChange(newDPI);
 
+    // update sizers
+    if ( GetSizer() )
+    {
+        wxSizerItemList::compatibility_iterator current =
+            GetSizer()->GetChildren().GetFirst();
+        while ( current )
+        {
+            wxSizerItem* sizerItem = current->GetData();
+
+            int border = sizerItem->GetBorder();
+            ScaleCoordIfSet(border, scaleFactor);
+            sizerItem->SetBorder(border);
+
+            // only scale sizers and spacers, not windows
+            if ( sizerItem->IsSizer() || sizerItem->IsSpacer() )
+            {
+                wxSize min = sizerItem->GetMinSize();
+                ScaleCoordIfSet(min.x, scaleFactor);
+                ScaleCoordIfSet(min.y, scaleFactor);
+                sizerItem->SetMinSize(min);
+
+                wxSize size = sizerItem->GetSize();
+                ScaleCoordIfSet(size.x, scaleFactor);
+                ScaleCoordIfSet(size.y, scaleFactor);
+                sizerItem->SetDimension(wxDefaultPosition, size);
+            }
+
+            current = current->GetNext();
+        }
+    }
+
     // update children
     wxWindowList::compatibility_iterator current = GetChildren().GetFirst();
     while ( current )