From 0ee25aaa7615f81c49adde0ba272416b39b28ccd Mon Sep 17 00:00:00 2001
From: Artur Wieczorek <artwik@wp.pl>
Date: Mon, 11 Apr 2016 18:06:42 +0200
Subject: [PATCH] Fixed creating Cairo bitmap from wxBitmap (wxMSW).

Iterating over bit values with wxAlphaPixelData sets the internal wxBitmap's "has alpha" flag but we want to left it unchanged so we have to save its original value and restore it afterward.
---
 src/generic/graphicc.cpp | 80 +++++++++++++++++++++++-----------------
 1 file changed, 47 insertions(+), 33 deletions(-)

diff --git a/src/generic/graphicc.cpp b/src/generic/graphicc.cpp
index 218d1d7435..2a32a1df23 100644
--- a/src/generic/graphicc.cpp
+++ b/src/generic/graphicc.cpp
@@ -1414,43 +1414,57 @@ wxCairoBitmapData::wxCairoBitmapData( wxGraphicsRenderer* renderer, const wxBitm
 
     if ( isSrcBpp32 )
     {
-        // use the bitmap's alpha
-        wxAlphaPixelData
-            pixData(bmpSource, wxPoint(0, 0), wxSize(m_width, m_height));
-        wxCHECK_RET( pixData, wxT("Failed to gain raw access to bitmap data."));
+        // Using wxAlphaPixelData sets (on wxMSW and wxOSX) the internal
+        // "has alpha" flag but we want to leave it unchanged, so we need
+        // to save its current value now and restore it afterwards.
+#if defined(__WXMSW__) || defined(__WXOSX__)
+        const bool hasAlpha = bmpSource.HasAlpha();
+#endif // __WXMSW__ || __WXOSX__
 
-        wxAlphaPixelData::Iterator p(pixData);
-        for (int y=0; y<m_height; y++)
         {
-            wxAlphaPixelData::Iterator rowStart = p;
-            wxUint32* const rowStartDst = data;
-            for (int x=0; x<m_width; x++)
-            {
-                // Each pixel in CAIRO_FORMAT_ARGB32 is a 32-bit quantity,
-                // with alpha in the upper 8 bits, then red, then green, then
-                // blue. The 32-bit quantities are stored native-endian.
-                // Pre-multiplied alpha is used.
-                unsigned char alpha = (bufferFormat == CAIRO_FORMAT_ARGB32) ? p.Alpha() : 255;
-#ifdef __WXMSW__
-                // MSW bitmap pixel bits are already premultiplied.
-                *data = (alpha << 24 | p.Red() << 16 | p.Green() << 8 | p.Blue());
-#else // !__WXMSW__
-                if (alpha == 0)
-                    *data = 0;
-                else
-                    *data = (alpha << 24
-                        | Premultiply(alpha, p.Red()) << 16
-                        | Premultiply(alpha, p.Green()) << 8
-                        | Premultiply(alpha, p.Blue()));
-#endif // __WXMSW__ / !__WXMSW__
-                ++data;
-                ++p;
-            }
+            // use the bitmap's alpha
+            wxAlphaPixelData pixData(bmpSource);
+            wxCHECK_RET( pixData, wxT("Failed to gain raw access to bitmap data."));
 
-            data = rowStartDst + stride / 4;
-            p = rowStart;
-            p.OffsetY(pixData, 1);
+            wxAlphaPixelData::Iterator p(pixData);
+            for (int y=0; y<m_height; y++)
+            {
+                wxAlphaPixelData::Iterator rowStart = p;
+                wxUint32* const rowStartDst = data;
+                for (int x=0; x<m_width; x++)
+                {
+                    // Each pixel in CAIRO_FORMAT_ARGB32 is a 32-bit quantity,
+                    // with alpha in the upper 8 bits, then red, then green, then
+                    // blue. The 32-bit quantities are stored native-endian.
+                    // Pre-multiplied alpha is used.
+                    unsigned char alpha = (bufferFormat == CAIRO_FORMAT_ARGB32) ? p.Alpha() : 255;
+#ifdef __WXMSW__
+                    // MSW bitmap pixel bits are already premultiplied.
+                    *data = (alpha << 24 | p.Red() << 16 | p.Green() << 8 | p.Blue());
+#else // !__WXMSW__
+                    if (alpha == 0)
+                        *data = 0;
+                    else
+                        *data = (alpha << 24
+                            | Premultiply(alpha, p.Red()) << 16
+                            | Premultiply(alpha, p.Green()) << 8
+                            | Premultiply(alpha, p.Blue()));
+#endif // __WXMSW__ / !__WXMSW__
+                    ++data;
+                    ++p;
+                }
+
+                data = rowStartDst + stride / 4;
+                p = rowStart;
+                p.OffsetY(pixData, 1);
+            }
         }
+
+#if defined(__WXMSW__) || defined(__WXOSX__)
+        // Reset "has alpha" flag back.
+        // (wxBitmap::UseAlpha() is used only on wxMSW and wxOSX.)
+        bmpSource.UseAlpha(hasAlpha);
+#endif // __WXMSW__ || __WXOSX__
     }
     else  // no alpha
     {