From: Vadim Zeitlin <vadim@wxwidgets.org>
Date: Tue, 22 Mar 2011 17:15:49 +0000 (+0000)
Subject: Don't consider fully opaque bitmaps as having alpha in wxMSW.
X-Git-Url: https://git.saurik.com/wxWidgets.git/commitdiff_plain/20ca5632798e70467bb90624cc66ef1f06ebcd28

Don't consider fully opaque bitmaps as having alpha in wxMSW.

Remove the alpha channel from the DIB we create not only if all of its pixels
are fully transparent but also if they are all fully opaque. This prevents us
from erroneously creating bitmaps with alpha channel when none is needed nor
expected.

Closes #13056.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@67287 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
---

diff --git a/src/msw/dib.cpp b/src/msw/dib.cpp
index da8b42d1fc..14a44e2339 100644
--- a/src/msw/dib.cpp
+++ b/src/msw/dib.cpp
@@ -760,7 +760,14 @@ wxImage wxDIB::ConvertToImage() const
     }
 
     const int bpp = GetDepth();
+
+    // Remember if we have any "real" transparency, i.e. either any partially
+    // transparent pixels or not all pixels are fully opaque or fully
+    // transparent.
     bool hasAlpha = false;
+    bool hasOpaque = false;
+    bool hasTransparent = false;
+
     if ( bpp == 32 )
     {
         // 32 bit bitmaps may be either 0RGB or ARGB and we don't know in
@@ -793,13 +800,30 @@ wxImage wxDIB::ConvertToImage() const
                 // premultiplication done in Create() above
                 const unsigned char a = *src;
                 *alpha++ = a;
+
+                // Check what kind of alpha do we have.
+                switch ( a )
+                {
+                    case 0:
+                        hasTransparent = true;
+                        break;
+
+                    default:
+                        // Anything in between means we have real transparency
+                        // and must use alpha channel.
+                        hasAlpha = true;
+                        break;
+
+                    case 255:
+                        hasOpaque = true;
+                        break;
+                }
+
                 if ( a > 0 )
                 {
                     dst[0] = (dst[0] * 255) / a;
                     dst[1] = (dst[1] * 255) / a;
                     dst[2] = (dst[2] * 255) / a;
-
-                    hasAlpha = true;
                 }
 
                 src++;
@@ -817,6 +841,9 @@ wxImage wxDIB::ConvertToImage() const
         srcLineStart += srcBytesPerLine;
     }
 
+    if ( hasOpaque && hasTransparent )
+        hasAlpha = true;
+
     if ( !hasAlpha && image.HasAlpha() )
         image.ClearAlpha();