From a99e58e0740f9a8ab5918e671dfe242c8baf48cf Mon Sep 17 00:00:00 2001
From: Artur Wieczorek <artwik@wp.pl>
Date: Thu, 21 Jan 2016 17:31:48 +0100
Subject: [PATCH] Add method to convert wxDIB to wxImage enforcing alpha
 channel values (wxMSW).

wxDIB::ConvertToImage called with Convert_AlphaAuto converts wxDIB to wxImage with automatic checking if 32 bpp DIB contains real alpha values (legacy way).
When it is called with Convert_AlphaAlwaysIf32bpp then automatic checking is disabled and 32 bpp DIB is unconditionally converted to ARGB wxImage.
---
 include/wx/msw/dib.h | 13 ++++++++++++-
 src/msw/dib.cpp      |  4 ++--
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/include/wx/msw/dib.h b/include/wx/msw/dib.h
index a78230639b..b74880312b 100644
--- a/include/wx/msw/dib.h
+++ b/include/wx/msw/dib.h
@@ -164,7 +164,18 @@ public:
     bool Create(const wxImage& image, PixelFormat pf = PixelFormat_PreMultiplied);
 
     // create wxImage having the same data as this DIB
-    wxImage ConvertToImage() const;
+
+    // Possible options of conversion to wxImage
+    enum ConversionFlags
+    {
+        // Determine whether 32bpp DIB contains real alpha channel
+        // and return wxImage with or without alpha channel values.
+        Convert_AlphaAuto,
+        // Assume that 32bpp DIB contains valid alpha channel and always
+        // return wxImage with alpha channel values in this case.
+        Convert_AlphaAlwaysIf32bpp
+    };
+    wxImage ConvertToImage(ConversionFlags flags = Convert_AlphaAuto) const;
 #endif // wxUSE_IMAGE
 
 
diff --git a/src/msw/dib.cpp b/src/msw/dib.cpp
index 66a28cbf3e..616c59c7a4 100644
--- a/src/msw/dib.cpp
+++ b/src/msw/dib.cpp
@@ -676,7 +676,7 @@ bool wxDIB::Create(const wxImage& image, PixelFormat pf)
     return true;
 }
 
-wxImage wxDIB::ConvertToImage() const
+wxImage wxDIB::ConvertToImage(ConversionFlags flags) const
 {
     wxCHECK_MSG( IsOk(), wxNullImage,
                     wxT("can't convert invalid DIB to wxImage") );
@@ -776,7 +776,7 @@ wxImage wxDIB::ConvertToImage() const
     if ( hasOpaque && hasTransparent )
         hasAlpha = true;
 
-    if ( !hasAlpha && image.HasAlpha() )
+    if ( !hasAlpha && image.HasAlpha() && flags == Convert_AlphaAuto )
         image.ClearAlpha();
 
     return image;