desktop, vcl: support transparency in VirtualDevices with user-provided memory

Change-Id: I65c31995c02a644aa436aecd065255fab38045e4

desktop/source/lib/init.cxx

@@ -755,10 +755,21 @@ void doc_paintTile (LibreOfficeKitDocument* pThis,
     InitSvpForLibreOfficeKit();
 
     ScopedVclPtrInstance< VirtualDevice > pDevice(nullptr, Size(1, 1), (sal_uInt16)32) ;
+
+    // Set background to transparent by default.
+    memset(pBuffer, 0, nCanvasWidth * nCanvasHeight * 4);
+    pDevice->SetBackground(Wallpaper(Color(COL_TRANSPARENT)));
+
     boost::shared_array< sal_uInt8 > aBuffer( pBuffer, NoDelete< sal_uInt8 >() );
+
+    // Allocate a separate buffer for the alpha device.
+    std::vector<sal_uInt8> aAlpha(nCanvasWidth * nCanvasHeight);
+    memset(aAlpha.data(), 0, nCanvasWidth * nCanvasHeight);
+    boost::shared_array<sal_uInt8> aAlphaBuffer(aAlpha.data(), NoDelete<sal_uInt8>());
+
     pDevice->SetOutputSizePixelScaleOffsetAndBuffer(
                 Size(nCanvasWidth, nCanvasHeight), Fraction(1.0), Point(),
-                aBuffer, true );
+                aBuffer, aAlphaBuffer, true );
 
     pDoc->paintTile(*pDevice.get(), nCanvasWidth, nCanvasHeight,
                     nTilePosX, nTilePosY, nTileWidth, nTileHeight);
@@ -772,6 +783,17 @@ void doc_paintTile (LibreOfficeKitDocument* pThis,
                     nTilePosX, nTilePosY, nTileWidth, nTileHeight);
 #endif
 
+    // Overwrite pBuffer's alpha channel with the separate alpha buffer.
+    for (int nRow = 0; nRow < nCanvasHeight; ++nRow)
+    {
+        for (int nCol = 0; nCol < nCanvasWidth; ++nCol)
+        {
+            const int nOffset = (nCanvasHeight * nRow) + nCol;
+            // VCL's transparent is 0, RGBA's transparent is 0xff.
+            pBuffer[nOffset * 4 +3] = 0xff - aAlpha[nOffset];
+        }
+    }
+
     static bool bDebug = getenv("LOK_DEBUG") != 0;
     if (bDebug)
     {

include/vcl/virdev.hxx

@@ -48,6 +48,7 @@ private:
                                                      const bool bTopDown );
     SAL_DLLPRIVATE bool ImplSetOutputSizePixel( const Size& rNewSize, bool bErase,
                                                 const basebmp::RawMemorySharedArray &pBuffer,
+                                                const basebmp::RawMemorySharedArray &pAlphaBuffer,
                                                 const bool bTopDown );
 
     VirtualDevice (const VirtualDevice &) SAL_DELETED_FUNCTION;
@@ -126,6 +127,7 @@ public:
                                                                 const Fraction& rScale,
                                                                 const Point& rNewOffset,
                                                                 const basebmp::RawMemorySharedArray &pBuffer,
+                                                                const basebmp::RawMemorySharedArray &pAlphaBuffer,
                                                                 const bool bTopDown = false );
     bool                SetOutputSize( const Size& rNewSize, bool bErase = true )
                             { return SetOutputSizePixel( LogicToPixel( rNewSize ), bErase ); }

vcl/source/gdi/virdev.cxx

@@ -393,6 +393,7 @@ void VirtualDevice::ImplFillOpaqueRectangle( const Rectangle& rRect )
 
 bool VirtualDevice::ImplSetOutputSizePixel( const Size& rNewSize, bool bErase,
                                             const basebmp::RawMemorySharedArray &pBuffer,
+                                            const basebmp::RawMemorySharedArray &pAlphaBuffer,
                                             const bool bTopDown )
 {
     if( InnerImplSetOutputSizePixel(rNewSize, bErase, pBuffer, bTopDown) )
@@ -409,7 +410,7 @@ bool VirtualDevice::ImplSetOutputSizePixel( const Size& rNewSize, bool bErase,
             {
                 mpAlphaVDev = VclPtr<VirtualDevice>::Create( *this, mnAlphaDepth );
                 mpAlphaVDev->InnerImplSetOutputSizePixel(rNewSize, bErase,
-                                                         basebmp::RawMemorySharedArray(),
+                                                         pAlphaBuffer,
                                                          bTopDown );
             }
 
@@ -443,13 +444,16 @@ void VirtualDevice::EnableRTL( bool bEnable )
 
 bool VirtualDevice::SetOutputSizePixel( const Size& rNewSize, bool bErase )
 {
-    return ImplSetOutputSizePixel( rNewSize, bErase, basebmp::RawMemorySharedArray(), false );
+    return ImplSetOutputSizePixel( rNewSize, bErase, basebmp::RawMemorySharedArray(), basebmp::RawMemorySharedArray(), false );
 }
 
 bool VirtualDevice::SetOutputSizePixelScaleOffsetAndBuffer(
     const Size& rNewSize, const Fraction& rScale, const Point& rNewOffset,
-    const basebmp::RawMemorySharedArray &pBuffer, const bool bTopDown )
+    const basebmp::RawMemorySharedArray &pBuffer, const basebmp::RawMemorySharedArray &pAlphaBuffer, const bool bTopDown )
 {
+    if (pAlphaBuffer)
+        mnAlphaDepth = 8;
+
     if (pBuffer) {
         MapMode mm = GetMapMode();
         mm.SetOrigin( rNewOffset );
@@ -457,7 +461,7 @@ bool VirtualDevice::SetOutputSizePixelScaleOffsetAndBuffer(
         mm.SetScaleY( rScale );
         SetMapMode( mm );
     }
-    return ImplSetOutputSizePixel( rNewSize, true, pBuffer, bTopDown );
+    return ImplSetOutputSizePixel( rNewSize, true, pBuffer, pAlphaBuffer, bTopDown );
 }
 
 void VirtualDevice::SetReferenceDevice( RefDevMode i_eRefDevMode )