From: Vadim Zeitlin <vadim@wxwidgets.org>
Date: Sun, 19 Nov 2006 12:35:16 +0000 (+0000)
Subject: unmultiply by alpha when converting from wxDIB to wxImage as the former uses premulti... 
X-Git-Url: https://git.saurik.com/wxWidgets.git/commitdiff_plain/0deb5fab34f3cc90d717347b7335297ff67cc1b3

unmultiply by alpha when converting from wxDIB to wxImage as the former uses premultiplied alpha but the latter does not (patch 1597063)


git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@43511 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
---

diff --git a/docs/changes.txt b/docs/changes.txt
index 7b0d6dbc25..7e54a29355 100644
--- a/docs/changes.txt
+++ b/docs/changes.txt
@@ -98,6 +98,7 @@ wxMSW:
 
 - Fixed version script problems when using configure with cygwin/mingw32.
 - Use system default paper size for printing instead of A4
+- Fix colours when converting wxBitmap with alpha to wxImage (nusi)
 
 2.7.2
 -----
diff --git a/src/msw/dib.cpp b/src/msw/dib.cpp
index ee17d5d2b1..0c89e7e5ad 100644
--- a/src/msw/dib.cpp
+++ b/src/msw/dib.cpp
@@ -775,14 +775,26 @@ wxImage wxDIB::ConvertToImage() const
             dst[1] = *src++;
             dst[0] = *src++;
 
-            dst += 3;
-
             if ( is32bit )
             {
                 if ( alpha )
-                    *alpha++ = *src;
+                {
+                    // wxImage uses non premultiplied alpha so undo
+                    // premultiplication done in Create() above
+                    const unsigned char a = *src;
+                    *alpha++ = a;
+                    if ( a > 0 )
+                    {
+                        dst[0] = (dst[0] * 255 - 127) / a;
+                        dst[1] = (dst[1] * 255 - 127) / a;
+                        dst[2] = (dst[2] * 255 - 127) / a;
+                    }
+                }
+
                 src++;
             }
+
+            dst += 3;
         }
 
         // pass to the previous line in the image