Change alpha behavour of OutputDevice::SetFillColor

It is pretty ugly bad on several levels.

Essentially what the currrent behaviour does is, if the fill color has an
transparency value, and draw some pixels, we just don't bother to write
anything to the color surface at all, we only write to the alpha surface.

(*) It is impossible to emulate efficiently when we switch to combined
    color+alpha surfaces
(*) It works completely differently to how every other graphics API in the
    world operates
(*) It makes no sense - it doesn't allow you to fill a shape with partially
    transparent color pixels (because it just doesn't bother writing to the
    color surface).

This behaviour dates back to "initial import", so sadly no reason why.

Noting that we are changing 3 things here:
(1) Setting a fill color with transparency will actually write to the color
    surface.
(2) Previously, SetFillColor(COL_TRANSPARENCY) was the same as
    SetFillColor(), now they mean different things
(3) SetFillColor(x) where x has tranparency will now actually affect the fill
    color of the alpha layer.
(4) VirtualDevice::SetOutputSizePixel will now erase/fill the device with
    data in cases where it previously would not (because previously the
    fill was ignored when background == COL_TRANSPARENT)

Change-Id: I4c8b371a436a4d1ffc4344c7d6b21932d861397d
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/180184
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

include/sfx2/LokControlHandler.hxx

@@ -152,7 +152,7 @@ public:
             = o3tl::convert(rTileRect, o3tl::Length::twip, o3tl::Length::mm100);
 
         // Resizes the virtual device so to contain the entries context
-        rDevice.SetOutputSizePixel(aOutputSize);
+        rDevice.SetOutputSizePixel(aOutputSize, /*bErase*/ false);
 
         rDevice.Push(vcl::PushFlags::MAPMODE);
         MapMode aDeviceMapMode(rDevice.GetMapMode());

sd/source/ui/unoidl/unomodel.cxx

@@ -3612,7 +3612,7 @@ void SdXImpressDocument::paintTile( VirtualDevice& rDevice,
 
     rDevice.SetMapMode( aMapMode );
 
-    rDevice.SetOutputSizePixel( Size(nOutputWidth, nOutputHeight) );
+    rDevice.SetOutputSizePixel( Size(nOutputWidth, nOutputHeight), /*bErase*/false );
 
     Point aPoint(nTilePosXHMM, nTilePosYHMM);
     Size aSize(nTileWidthHMM, nTileHeightHMM);

sfx2/source/view/lokcharthelper.cxx

@@ -241,7 +241,7 @@ void LokChartHelper::PaintAllChartsOnTile(VirtualDevice& rDevice,
         return;
 
     // Resizes the virtual device so to contain the entries context
-    rDevice.SetOutputSizePixel(Size(nOutputWidth, nOutputHeight));
+    rDevice.SetOutputSizePixel(Size(nOutputWidth, nOutputHeight), /*bErase*/false);
 
     rDevice.Push(vcl::PushFlags::MAPMODE);
     MapMode aMapMode(rDevice.GetMapMode());

sw/source/core/view/viewsh.cxx

@@ -2112,7 +2112,7 @@ void SwViewShell::PaintTile(VirtualDevice &rDevice, int contextWidth, int contex
     mpOut = &rDevice;
 
     // resizes the virtual device so to contain the entries context
-    rDevice.SetOutputSizePixel(Size(contextWidth, contextHeight));
+    rDevice.SetOutputSizePixel(Size(contextWidth, contextHeight), /*bErase*/false);
 
     // setup the output device to draw the tile
     MapMode aMapMode(rDevice.GetMapMode());

vcl/qa/cppunit/outdev.cxx

@@ -511,7 +511,7 @@ CPPUNIT_TEST_FIXTURE(VclOutdevTest, testTransparentFillColor)
     CPPUNIT_ASSERT_EQUAL(COL_WHITE, pVDev->GetFillColor());
 
     pVDev->SetFillColor(COL_TRANSPARENT);
-    CPPUNIT_ASSERT(!pVDev->IsFillColor());
+    CPPUNIT_ASSERT(pVDev->IsFillColor());
     CPPUNIT_ASSERT_EQUAL(COL_TRANSPARENT, pVDev->GetFillColor());
     MetaAction* pAction = aMtf.GetAction(0);
     CPPUNIT_ASSERT_EQUAL(MetaActionType::FILLCOLOR, pAction->GetType());

vcl/source/outdev/fill.cxx

@@ -50,27 +50,18 @@ void OutputDevice::SetFillColor( const Color& rColor )
     if ( mpMetaFile )
         mpMetaFile->AddAction( new MetaFillColorAction( aColor, true ) );
 
-    if ( aColor.IsTransparent() )
+    if ( maFillColor != aColor )
     {
-        if ( mbFillColor )
-        {
-            mbInitFillColor = true;
-            mbFillColor = false;
-            maFillColor = COL_TRANSPARENT;
-        }
-    }
-    else
-    {
-        if ( maFillColor != aColor )
-        {
-            mbInitFillColor = true;
-            mbFillColor = true;
-            maFillColor = aColor;
-        }
+        mbInitFillColor = true;
+        mbFillColor = true;
+        maFillColor = aColor;
     }
 
     if( mpAlphaVDev )
-        mpAlphaVDev->SetFillColor( COL_ALPHA_OPAQUE );
+    {
+        sal_uInt8 nAlpha = rColor.GetAlpha();
+        mpAlphaVDev->SetFillColor( Color(nAlpha, nAlpha, nAlpha) );
+    }
 }
 
 void OutputDevice::InitFillColor()