added wxImage::ConvertAlphaToMask

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@28810 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/latex/wx/image.tex

@@ -257,6 +257,22 @@ WX_DECLARE_EXPORTED_HASH_MAP(unsigned long, wxImageHistogramEntry,
 
 Returns number of colours in the histogram.
 
+\membersection{wxImage::ConvertAlphaToMask}\label{wximageconvertalphatomask}
+
+\func{bool}{ConvertAlphaToMask}{\param{unsigned char}{ threshold = 128}}
+
+If the image has alpha channel, this method converts it to mask. All pixels
+with alpha value less than \arg{threshold} are replaced with mask colour
+and the alpha channel is removed. Mask colour is chosen automatically using
+\helpref{FindFirstUnusedColour}{wximagefindfirstunusedcolour}.
+
+If the image image doesn't have alpha channel,
+ConvertAlphaToMask does nothing.
+
+\wxheading{Return value}
+
+\false if FindFirstUnusedColour returns \false, \true otherwise. 
+
 \membersection{wxImage::ConvertToBitmap}\label{wximageconverttobitmap}
 
 \constfunc{wxBitmap}{ConvertToBitmap}{\void}