Add wxBitmap::SetScaleFactor()

We need to be able to change the scale factor of the bitmaps returned by
wxBitmapBundle::GetBitmap(), so add a function allowing to do this.

Also add wxHAS_BITMAP_SCALE_FACTOR allowing to check whether this
function actually does something non-trivial and explain in the docs
that GetScaleFactor() always returns 1 on the platforms where this
symbol is not defined.

docs/doxygen/mainpages/const_cpp.h

@@ -167,6 +167,9 @@ Currently the following symbols exist:
     have an efficient (CPU-specific) implementation. Notice that the functions
     themselves are always available but can be prohibitively slow to use when
     implemented in a generic way, using a critical section.}
+@itemdef{wxHAS_BITMAP_SCALE_FACTOR, Defined in @c wx/bitmap.h if bitmaps
+    actually use scale factor under the current platform, see
+    wxBitmap::SetScaleFactor().}
 @itemdef{wxHAS_BITMAPTOGGLEBUTTON, Defined in @c wx/tglbtn.h if
     wxBitmapToggleButton class is available in addition to wxToggleButton.}
 @itemdef{wxHAS_CONFIG_TEMPLATE_RW, Defined if the currently used compiler

include/wx/bitmap.h

@@ -188,6 +188,7 @@ public:
         { return wxSize(GetWidth(), GetHeight()); }
 
     // support for scaled bitmaps
+    virtual void SetScaleFactor(double WXUNUSED(scale)) { }
     virtual double GetScaleFactor() const { return 1.0; }
     virtual double GetScaledWidth() const { return GetWidth() / GetScaleFactor(); }
     virtual double GetScaledHeight() const { return GetHeight() / GetScaleFactor(); }

include/wx/gtk/bitmap.h

@@ -17,6 +17,10 @@ typedef struct _GdkPixbuf GdkPixbuf;
 class WXDLLIMPEXP_FWD_CORE wxPixelDataBase;
 class WXDLLIMPEXP_FWD_CORE wxCursor;
 
+#ifdef __WXGTK3__
+    #define wxHAS_BITMAP_SCALE_FACTOR
+#endif
+
 //-----------------------------------------------------------------------------
 // wxMask
 //-----------------------------------------------------------------------------
@@ -85,8 +89,9 @@ public:
         { return Create(sz.GetWidth(), sz.GetHeight(), depth); }
     bool Create(int width, int height, const wxDC& WXUNUSED(dc))
         { return Create(width,height); }
-#ifdef __WXGTK3__
+#ifdef wxHAS_BITMAP_SCALE_FACTOR
     virtual bool CreateScaled(int w, int h, int depth, double scale) wxOVERRIDE;
+    virtual void SetScaleFactor(double scale) wxOVERRIDE;
     virtual double GetScaleFactor() const wxOVERRIDE;
 #endif
 

include/wx/msw/bitmap.h

@@ -186,6 +186,7 @@ public:
     void ResetAlpha() { UseAlpha(false); }
 
     // support for scaled bitmaps
+    virtual void SetScaleFactor(double WXUNUSED(scale)) { }
     virtual double GetScaleFactor() const { return 1.0; }
     virtual double GetScaledWidth() const { return GetWidth(); }
     virtual double GetScaledHeight() const { return GetHeight(); }

include/wx/osx/bitmap.h

@@ -13,6 +13,8 @@
 
 #include "wx/palette.h"
 
+#define wxHAS_BITMAP_SCALE_FACTOR
+
 // Bitmap
 class WXDLLIMPEXP_FWD_CORE wxBitmap;
 class wxBitmapRefData ;
@@ -239,6 +241,7 @@ public:
     void EndRawAccess();
 #endif
 
+    void SetScaleFactor(double scale) wxOVERRIDE;
     double GetScaleFactor() const wxOVERRIDE;
 
     void SetSelectedInto(wxDC *dc);

interface/wx/bitmap.h

@@ -469,7 +469,7 @@ public:
         @param depth
             The number of bits used to represent each bitmap pixel.
         @param logicalScale
-            Scale factor used by the bitmap
+            Scale factor used by the bitmap, see SetScaleFactor().
 
         @return @true if the creation was successful.
 
@@ -586,9 +586,10 @@ public:
         1 must be used in high DPI to appear sharp on the screen.
 
         Note that the scale factor is only used in the ports where logical
-        pixels are not the same as physical ones, such as wxOSX or wxGTK3.
+        pixels are not the same as physical ones, such as wxOSX or wxGTK3, and
+        this function always returns 1 under the other platforms.
 
-        @see GetScaledWidth(), GetScaledHeight(), GetScaledSize()
+        @see SetScaleFactor(), GetScaledWidth(), GetScaledHeight(), GetScaledSize()
 
         @since 2.9.5
      */
@@ -796,6 +797,38 @@ public:
     */
     virtual void SetHeight(int height);
 
+    /**
+        Sets the bitmap scale factor.
+
+        This doesn't change the bitmap actual size or its contents, but changes
+        its scale factor, so that it appears in a smaller size when it is drawn
+        on screen: e.g. setting @a scale to 2 means that the bitmap will be
+        twice smaller (in each direction) when drawn on screen in the ports in
+        which logical and physical pixels differ (i.e. wxOSX and wxGTK3, but
+        not wxMSW).
+
+        When creating a new bitmap, CreateScaled() can be used to specify the
+        correct scale factor from the beginning.
+
+        Note that this method exists in all ports, but simply does nothing in
+        those of them that don't use logical pixel scaling. The preprocessor
+        symbol @c wxHAS_BITMAP_SCALE_FACTOR can be tested to determine whether
+        the scale factor is really supported, e.g.
+
+        @code
+            bitmap.SetScaleFactor(2);
+
+            // In the other ports scale factor is always 1, so the assert would
+            // fail there.
+            #ifdef wxHAS_BITMAP_SCALE_FACTOR
+                wxASSERT( bitmap.GetScaleFactor() == 2 );
+            #endif
+        @endcode
+
+        @since 3.1.6
+     */
+    virtual void SetScaleFactor(double scale);
+
     /**
         Sets the mask for this bitmap.
 

src/gtk/bitmap.cpp

@@ -1002,6 +1002,13 @@ bool wxBitmap::CreateScaled(int w, int h, int depth, double scale)
     return true;
 }
 
+void wxBitmap::SetScaleFactor(double scale)
+{
+    wxCHECK_RET(m_refData, "invalid bitmap");
+
+    M_BMPDATA->m_scaleFactor = scale;
+}
+
 double wxBitmap::GetScaleFactor() const
 {
     wxCHECK_MSG(m_refData, -1, "invalid bitmap");

src/osx/core/bitmap.cpp

@@ -75,6 +75,8 @@ public:
     int GetBytesPerRow() const;
     bool HasAlpha() const;
     WXImage GetImage() const;
+
+    void SetScaleFactor(double scale) { m_scaleFactor = scale; }
     double GetScaleFactor() const { return m_scaleFactor; }
 
     const void *GetRawAccess() const;
@@ -1389,6 +1391,13 @@ int wxBitmap::GetWidth() const
    return GetBitmapData()->GetWidth() ;
 }
 
+void wxBitmap::SetScaleFactor(double scale)
+{
+    wxCHECK_RET( IsOk(), wxT("invalid bitmap") );
+
+    return GetBitmapData()->SetScaleFactor(scale) ;
+}
+
 double wxBitmap::GetScaleFactor() const
 {
     wxCHECK_MSG( IsOk(), -1, wxT("invalid bitmap") );