allow specifying the mask colour in wxImage::ConvertAlphaToMask() (closes #10143)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@58404 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/image.h

@@ -322,9 +322,13 @@ public:
     bool SetMaskFromImage(const wxImage & mask,
                           unsigned char mr, unsigned char mg, unsigned char mb);
 
-    // converts image's alpha channel to mask, if it has any, does nothing
+    // converts image's alpha channel to mask (choosing mask colour
-    // otherwise:
+    // automatically or using the specified colour for the mask), if it has
+    // any, does nothing otherwise:
     bool ConvertAlphaToMask(unsigned char threshold = wxIMAGE_ALPHA_THRESHOLD);
+    void ConvertAlphaToMask(unsigned char mr, unsigned char mg, unsigned char mb,
+                            unsigned char threshold = wxIMAGE_ALPHA_THRESHOLD);
+
 
     // This method converts an image where the original alpha
     // information is only available as a shades of a colour

interface/wx/image.h

@@ -519,19 +519,49 @@ public:
     */
     unsigned long ComputeHistogram(wxImageHistogram& histogram) const;
 
+    //@{
     /**
         If the image has alpha channel, this method converts it to mask.
 
-        All pixels with alpha value less than @a threshold are replaced with mask
+        If the image has an alpha channel, all pixels with alpha value less
-        colour and the alpha channel is removed. Mask colour is chosen automatically
+        than @a threshold are replaced with the mask colour and the alpha
-        using FindFirstUnusedColour().
+        channel is removed. Otherwise nothing is done.
         
-        If the image image doesn't have alpha channel, ConvertAlphaToMask() does nothing.
+        The mask colour is chosen automatically using
+        FindFirstUnusedColour() by this function, see the overload below if you
+        this is not appropriate.
 
         @return @false if FindFirstUnusedColour returns @false, @true otherwise.
     */
     bool ConvertAlphaToMask(unsigned char threshold = wxIMAGE_ALPHA_THRESHOLD);
 
+    /**
+        If the image has alpha channel, this method converts it to mask using
+        the specified colour as the mask colour.
+
+        If the image has an alpha channel, all pixels with alpha value less
+        than @a threshold are replaced with the mask colour and the alpha
+        channel is removed. Otherwise nothing is done.
+
+        @since 2.9.0
+
+        @param mr
+            The red component of the mask colour.
+        @param mg
+            The green component of the mask colour.
+        @param mb
+            The blue component of the mask colour.
+        @param threshold
+            Pixels with alpha channel values below the given threshold are
+            considered to be transparent, i.e. the corresponding mask pixels
+            are set. Pixels with the alpha values above the threshold are
+            considered to be opaque.
+
+     */
+    void ConvertAlphaToMask(unsigned char mr, unsigned char mg, unsigned char mb, 
+                            unsigned char threshold = wxIMAGE_ALPHA_THRESHOLD);
+    //@}
+
     /**
         Returns a greyscale version of the image.
 

src/common/image.cpp

@@ -1905,16 +1905,28 @@ bool wxImage::SetMaskFromImage(const wxImage& mask,
 
 bool wxImage::ConvertAlphaToMask(unsigned char threshold)
 {
-    if (!HasAlpha())
+    if ( !HasAlpha() )
         return true;
 
     unsigned char mr, mg, mb;
-    if (!FindFirstUnusedColour(&mr, &mg, &mb))
+    if ( !FindFirstUnusedColour(&mr, &mg, &mb) )
     {
         wxLogError( _("No unused colour in image being masked.") );
         return false;
     }
 
+    ConvertAlphaToMask(mr, mg, mb, threshold);
+    return true;
+}
+
+void wxImage::ConvertAlphaToMask(unsigned char mr,
+                                 unsigned char mg,
+                                 unsigned char mb,
+                                 unsigned char threshold)
+{
+    if ( !HasAlpha() )
+        return;
+
     AllocExclusive();
 
     SetMask(true);
@@ -1939,13 +1951,11 @@ bool wxImage::ConvertAlphaToMask(unsigned char threshold)
         }
     }
 
-    if( !M_IMGDATA->m_staticAlpha )
+    if ( !M_IMGDATA->m_staticAlpha )
         free(M_IMGDATA->m_alpha);
 
     M_IMGDATA->m_alpha = NULL;
     M_IMGDATA->m_staticAlpha = false;
-
-    return true;
 }
 
 // ----------------------------------------------------------------------------