fdo#74702 Refactor OutputDevice::DrawTransparent()

I have refactored OutputDevice::DrawTransparent() - functionality
is now in the functions DrawInvisiblePolygon(),
DrawTransparentNatively() and EmulateDrawTransparent().

DrawTransparentNatively() will return true if it is successful,
otherwise it will return false if it isn't possible to draw the
transparency natively. This allows us to fall back to a VCL based
emulation.

The function EmulateDrawTransparent() is virtual because Printer
handles transparencies differently to pixel based devices.

Change-Id: I300850ccea03c17673666dadd287bcddd40ec5ef
Reviewed-on: https://gerrit.libreoffice.org/8779Reviewed-by: Chris Sherlock <chris.sherlock79@gmail.com>
Tested-by: Chris Sherlock <chris.sherlock79@gmail.com>

include/vcl/outdev.hxx

@@ -805,6 +805,7 @@ protected:
                                                 const Point& rSrcPtPixel, const Size& rSrcSizePixel );
 
     virtual long                ImplGetGradientStepCount( long nMinRect );
+
     /** Transform and draw a bitmap directly
 
      @param     aFullTransform      The B2DHomMatrix used for the transformation
@@ -839,6 +840,8 @@ protected:
                                     const Point& rSrcPtPixel, const Size& rSrcSizePixel,
                                     BitmapEx& rBitmapEx );
 
+    virtual void                EmulateDrawTransparent( const PolyPolygon& rPolyPoly, sal_uInt16 nTransparencePercent );
+    void                        DrawInvisiblePolygon( const PolyPolygon& rPolyPoly );
 
 private:
     typedef void ( OutputDevice::* FontUpdateHandler_t )( bool );
@@ -852,7 +855,9 @@ private:
     SAL_DLLPRIVATE long         ImplGetGradientSteps( const Gradient& rGradient, const Rectangle& rRect, bool bMtf );
 
     // not implemented; to detect misuses of DrawOutDev(...OutputDevice&);
-    void DrawOutDev( const Point&, const Size&, const Point&,  const Size&, const Printer&);
+    void                        DrawOutDev( const Point&, const Size&, const Point&,  const Size&, const Printer&);
+
+    bool                        DrawTransparentNatively( const PolyPolygon& rPolyPoly, sal_uInt16 nTransparencePercent );
 
 public:
     virtual                     ~OutputDevice();

include/vcl/print.hxx

@@ -286,6 +286,7 @@ protected:
     virtual void                ImplPrintMask ( const Bitmap& rMask, const Color& rMaskColor,
                                                 const Point& rDestPt, const Size& rDestSize,
                                                 const Point& rSrcPtPixel, const Size& rSrcSizePixel ) SAL_OVERRIDE;
+
     bool                        DrawTransformBitmapExDirect(
                                     const basegfx::B2DHomMatrix& aFullTransform,
                                     const BitmapEx& rBitmapEx) SAL_OVERRIDE;
@@ -300,6 +301,8 @@ protected:
                                     const Point& rSrcPtPixel, const Size& rSrcSizePixel,
                                     BitmapEx& rBitmapEx ) SAL_OVERRIDE;
 
+    virtual void                EmulateDrawTransparent( const PolyPolygon& rPolyPoly, sal_uInt16 nTransparencePercent ) SAL_OVERRIDE;
+
 public:
                                 Printer();
                                 Printer( const JobSetup& rJobSetup );

vcl/source/gdi/print.cxx

@@ -250,6 +250,85 @@ void Printer::DrawDeviceBitmap( const Point& rDestPt, const Size& rDestSize,
     }
 }
 
+
+void Printer::EmulateDrawTransparent ( const PolyPolygon& rPolyPoly,
+                                       sal_uInt16 nTransparencePercent )
+{
+    // #110958# Disable alpha VDev, we perform the necessary
+    VirtualDevice* pOldAlphaVDev = mpAlphaVDev;
+
+    // operation explicitly further below.
+    if( mpAlphaVDev )
+        mpAlphaVDev = NULL;
+
+    GDIMetaFile* pOldMetaFile = mpMetaFile;
+    mpMetaFile = NULL;
+
+    mpMetaFile = pOldMetaFile;
+
+    // #110958# Restore disabled alpha VDev
+    mpAlphaVDev = pOldAlphaVDev;
+
+    Rectangle       aPolyRect( LogicToPixel( rPolyPoly ).GetBoundRect() );
+    const Size      aDPISize( LogicToPixel( Size( 1, 1 ), MAP_INCH ) );
+    const long      nBaseExtent = std::max( FRound( aDPISize.Width() / 300. ), 1L );
+    long            nMove;
+    const sal_uInt16    nTrans = ( nTransparencePercent < 13 ) ? 0 :
+        ( nTransparencePercent < 38 ) ? 25 :
+        ( nTransparencePercent < 63 ) ? 50 :
+        ( nTransparencePercent < 88 ) ? 75 : 100;
+
+    switch( nTrans )
+    {
+        case( 25 ): nMove = nBaseExtent * 3; break;
+        case( 50 ): nMove = nBaseExtent * 4; break;
+        case( 75 ): nMove = nBaseExtent * 6; break;
+
+            // #i112959#  very transparent (88 < nTransparencePercent <= 99)
+        case( 100 ): nMove = nBaseExtent * 8; break;
+
+            // #i112959# not transparent (nTransparencePercent < 13)
+        default:    nMove = 0; break;
+    }
+
+    Push( PUSH_CLIPREGION | PUSH_LINECOLOR );
+    IntersectClipRegion(Region(rPolyPoly));
+    SetLineColor( GetFillColor() );
+    const bool bOldMap = mbMap;
+    EnableMapMode( false );
+
+    if(nMove)
+    {
+        Rectangle aRect( aPolyRect.TopLeft(), Size( aPolyRect.GetWidth(), nBaseExtent ) );
+        while( aRect.Top() <= aPolyRect.Bottom() )
+        {
+            DrawRect( aRect );
+            aRect.Move( 0, nMove );
+        }
+
+        aRect = Rectangle( aPolyRect.TopLeft(), Size( nBaseExtent, aPolyRect.GetHeight() ) );
+        while( aRect.Left() <= aPolyRect.Right() )
+        {
+            DrawRect( aRect );
+            aRect.Move( nMove, 0 );
+        }
+    }
+    else
+    {
+        // #i112959# if not transparent, draw full rectangle in clip region
+        DrawRect( aPolyRect );
+    }
+
+    EnableMapMode( bOldMap );
+    Pop();
+
+    mpMetaFile = pOldMetaFile;
+
+    // #110958# Restore disabled alpha VDev
+    mpAlphaVDev = pOldAlphaVDev;
+}
+
+
 void Printer::DrawOutDev( const Point& /*rDestPt*/, const Size& /*rDestSize*/,
                                const Point& /*rSrcPt*/,  const Size& /*rSrcSize*/ )
 {