Add wxDPIChangedEvent::Scale() and use it in this event handlers

This is more concise and less error-prone than multiplying/dividing DPI
values manually.

No real changes except, maybe, in wxSlider code where the rounding was
done differently before for some reason.

include/wx/event.h

@@ -3140,6 +3140,13 @@ public:
     wxSize GetOldDPI() const { return m_oldDPI; }
     wxSize GetNewDPI() const { return m_newDPI; }
 
+    // Scale the value by the ratio between new and old DPIs carried by this
+    // event.
+    int ScaleX(int x) const { return wxRescaleCoord(x, m_newDPI.x, m_oldDPI.x); }
+    int ScaleY(int y) const { return wxRescaleCoord(y, m_newDPI.y, m_oldDPI.y); }
+
+    wxSize Scale(wxSize sz) const { return wxSize(ScaleX(sz.x), ScaleY(sz.y)); }
+
     virtual wxEvent *Clone() const wxOVERRIDE { return new wxDPIChangedEvent(*this); }
 
 private:

interface/wx/event.h

@@ -3444,6 +3444,38 @@ public:
         Returns the new DPI.
     */
     wxSize GetNewDPI() const;
+
+    /**
+        Rescale a value in pixels to match the new DPI.
+
+        This is a convenience function to use in wxEVT_DPI_CHANGED event
+        handlers, as they often need to update some sizes to the new DPI.
+        It simply calls wxRescaleCoord() with GetNewDPI() and GetOldDPI().
+
+        For example, the returned value will be twice bigger than the original
+        one when switching from normal (96) DPI to high (2x, 192) DPI.
+
+        @since 3.1.6
+     */
+    wxSize Scale(wxSize sz) const;
+
+    /**
+        Rescale horizontal component to match the new DPI.
+
+        This is the same as Scale(), but for the horizontal component only.
+
+        @since 3.1.6
+     */
+    int ScaleX(int x) const;
+
+    /**
+        Rescale vertical component to match the new DPI.
+
+        This is the same as Scale(), but for the vertical component only.
+
+        @since 3.1.6
+     */
+    int ScaleY(int y) const;
 };
 
 

src/generic/datavgen.cpp

@@ -5669,12 +5669,12 @@ void wxDataViewCtrl::OnDPIChanged(wxDPIChangedEvent& event)
     {
         int minWidth = m_cols[i]->GetMinWidth();
         if ( minWidth > 0 )
-            minWidth = minWidth * event.GetNewDPI().x / event.GetOldDPI().x;
+            minWidth = event.ScaleX(minWidth);
         m_cols[i]->SetMinWidth(minWidth);
 
         int width = m_cols[i]->WXGetSpecifiedWidth();
         if ( width > 0 )
-            width = width * event.GetNewDPI().x / event.GetOldDPI().x;
+            width = event.ScaleX(width);
         m_cols[i]->SetWidth(width);
     }
 }

src/generic/grid.cpp

@@ -5781,7 +5781,7 @@ void wxGrid::OnDPIChanged(wxDPIChangedEvent& event)
             if ( height <= 0 )
                 continue;
 
-            height = height * event.GetNewDPI().x / event.GetOldDPI().x;
+            height = event.ScaleY(height);
             total += height;
 
             m_rowHeights[i] = height;
@@ -5804,7 +5804,7 @@ void wxGrid::OnDPIChanged(wxDPIChangedEvent& event)
             if ( width <= 0 )
                 continue;
 
-            width = width * event.GetNewDPI().x / event.GetOldDPI().x;
+            width = event.ScaleX(width);
             total += width;
 
             m_colWidths[i] = width;

src/msw/listctrl.cpp

@@ -446,9 +446,10 @@ void wxListCtrl::OnDPIChanged(wxDPIChangedEvent &event)
     for ( int i = 0; i < numCols; ++i )
     {
         int width = GetColumnWidth(i);
-        if ( width > 0 )
-            width = width * event.GetNewDPI().x / event.GetOldDPI().x;
-        SetColumnWidth(i, width);
+        if ( width <= 0 )
+            continue;
+
+        SetColumnWidth(i, event.ScaleX(width));
     }
 }
 

src/msw/slider.cpp

@@ -653,11 +653,7 @@ void wxSlider::OnDPIChanged(wxDPIChangedEvent& event)
 {
     int thumbLen = GetThumbLength();
 
-    const double scaleFactor = (double)event.GetNewDPI().x / event.GetOldDPI().x;
-    const double thumbLenScaled = thumbLen * scaleFactor;
-    thumbLen = (int)(scaleFactor > 1.0 ? ceil(thumbLenScaled) : floor(thumbLenScaled));
-
-    SetThumbLength(thumbLen);
+    SetThumbLength(event.ScaleX(thumbLen));
 }
 
 // ----------------------------------------------------------------------------

src/msw/toolbar.cpp

@@ -1949,8 +1949,6 @@ void wxToolBar::OnDPIChanged(wxDPIChangedEvent& event)
 {
     // Manually scale the size of the controls. Even though the font has been
     // updated, the internal size of the controls does not.
-    const float scaleFactor = (float)event.GetNewDPI().y / event.GetOldDPI().y;
-
     wxToolBarToolsList::compatibility_iterator node;
     for ( node = m_tools.GetFirst(); node; node = node->GetNext() )
     {
@@ -1961,7 +1959,7 @@ void wxToolBar::OnDPIChanged(wxDPIChangedEvent& event)
         if ( wxControl* const control = tool->GetControl() )
         {
             const wxSize oldSize = control->GetSize();
-            wxSize newSize = oldSize * scaleFactor;
+            wxSize newSize = event.Scale(oldSize);
 
             // Use the best height for choice-based controls.
             // Scaling the current size does not work, because the control

src/stc/stc.cpp

@@ -5441,7 +5441,7 @@ void wxStyledTextCtrl::OnDPIChanged(wxDPIChangedEvent& evt) {
     // adjust the margins to the new DPI
     for ( int i = 0; i < SC_MAX_MARGIN; ++i )
     {
-        SetMarginWidth(i, (int)wxMulDivInt32(GetMarginWidth(i), evt.GetNewDPI().y, evt.GetOldDPI().y));
+        SetMarginWidth(i, evt.ScaleY(GetMarginWidth(i)));
     }
 
     // Hide auto-complete popup, there is no (easy) way to set it to the correct size

src/stc/stc.cpp.in

@@ -968,7 +968,7 @@ void wxStyledTextCtrl::OnDPIChanged(wxDPIChangedEvent& evt) {
     // adjust the margins to the new DPI
     for ( int i = 0; i < SC_MAX_MARGIN; ++i )
     {
-        SetMarginWidth(i, (int)wxMulDivInt32(GetMarginWidth(i), evt.GetNewDPI().y, evt.GetOldDPI().y));
+        SetMarginWidth(i, evt.ScaleY(GetMarginWidth(i)));
     }
 
     // Hide auto-complete popup, there is no (easy) way to set it to the correct size