fix erasing virtual device with alpha

The background cannot be simply set as background also for the internal
alpha virtual device, since this hackish alpha uses black = opaque
and white = transparent. So e.g. setting to background to COL_WHITE
actually resulted in the content being transparent.
Try to map to what the alpha virtual device actually needs.

Change-Id: Ie5179769d9bce989eddfc96f5cbd2b94d1d88d53
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/101927
Tested-by: Jenkins
Reviewed-by: Luboš Luňák <l.lunak@collabora.com>

2 files changed, 106 insertions, 2 deletions

diff --git a/vcl/qa/cppunit/BackendTest.cxx b/vcl/qa/cppunit/BackendTest.cxx
index 45793434dd1b..0e3d9c54dd08 100644
--- a/vcl/qa/cppunit/BackendTest.cxx
+++ b/vcl/qa/cppunit/BackendTest.cxx
@@ -49,7 +49,7 @@ class BackendTest : public test::BootstrapFixture
     {
         if (mbExportBitmap)
         {
-            BitmapEx aBitmapEx(device->GetBitmap(Point(0, 0), device->GetOutputSizePixel()));
+            BitmapEx aBitmapEx(device->GetBitmapEx(Point(0, 0), device->GetOutputSizePixel()));
             SvFileStream aStream(filename, StreamMode::WRITE | StreamMode::TRUNC);
             GraphicFilter::GetGraphicFilter().compressAsPNG(aBitmapEx, aStream);
         }
@@ -517,6 +517,71 @@ public:
 
     // vcl::test::OutputDeviceTestGradient does not verify anything, cannot test here
 
+    void testErase()
+    {
+        {
+            // Create normal virtual device (no alpha).
+            ScopedVclPtr<VirtualDevice> device
+                = VclPtr<VirtualDevice>::Create(DeviceFormat::DEFAULT);
+            device->SetOutputSizePixel(Size(10, 10));
+            // Erase with white, check it's white.
+            device->SetBackground(Wallpaper(COL_WHITE));
+            device->Erase();
+            exportDevice("/tmp/12-01_erase.png", device);
+            CPPUNIT_ASSERT_EQUAL(COL_WHITE, device->GetPixel(Point(0, 0)));
+            CPPUNIT_ASSERT_EQUAL(COL_WHITE, device->GetPixel(Point(9, 9)));
+            CPPUNIT_ASSERT_EQUAL(COL_WHITE, device->GetPixel(Point(5, 5)));
+            // Erase with black, check it's black.
+            device->SetBackground(Wallpaper(COL_BLACK));
+            device->Erase();
+            exportDevice("/tmp/12-02_erase.png", device);
+            CPPUNIT_ASSERT_EQUAL(COL_BLACK, device->GetPixel(Point(0, 0)));
+            CPPUNIT_ASSERT_EQUAL(COL_BLACK, device->GetPixel(Point(9, 9)));
+            CPPUNIT_ASSERT_EQUAL(COL_BLACK, device->GetPixel(Point(5, 5)));
+            // Erase with cyan, check it's cyan.
+            device->SetBackground(Wallpaper(COL_CYAN));
+            device->Erase();
+            exportDevice("/tmp/12-03_erase.png", device);
+            CPPUNIT_ASSERT_EQUAL(COL_CYAN, device->GetPixel(Point(0, 0)));
+            CPPUNIT_ASSERT_EQUAL(COL_CYAN, device->GetPixel(Point(9, 9)));
+            CPPUNIT_ASSERT_EQUAL(COL_CYAN, device->GetPixel(Point(5, 5)));
+        }
+        {
+            // Create virtual device with alpha.
+            ScopedVclPtr<VirtualDevice> device
+                = VclPtr<VirtualDevice>::Create(DeviceFormat::DEFAULT, DeviceFormat::DEFAULT);
+            device->SetOutputSizePixel(Size(10, 10));
+            // Erase with white, check it's white.
+            device->SetBackground(Wallpaper(COL_WHITE));
+            device->Erase();
+            exportDevice("/tmp/12-04_erase.png", device);
+            CPPUNIT_ASSERT_EQUAL(COL_WHITE, device->GetPixel(Point(0, 0)));
+            CPPUNIT_ASSERT_EQUAL(COL_WHITE, device->GetPixel(Point(9, 9)));
+            CPPUNIT_ASSERT_EQUAL(COL_WHITE, device->GetPixel(Point(5, 5)));
+            // Erase with black, check it's black.
+            device->SetBackground(Wallpaper(COL_BLACK));
+            device->Erase();
+            exportDevice("/tmp/12-05_erase.png", device);
+            CPPUNIT_ASSERT_EQUAL(COL_BLACK, device->GetPixel(Point(0, 0)));
+            CPPUNIT_ASSERT_EQUAL(COL_BLACK, device->GetPixel(Point(9, 9)));
+            CPPUNIT_ASSERT_EQUAL(COL_BLACK, device->GetPixel(Point(5, 5)));
+            // Erase with cyan, check it's cyan.
+            device->SetBackground(Wallpaper(COL_CYAN));
+            device->Erase();
+            exportDevice("/tmp/12-06_erase.png", device);
+            CPPUNIT_ASSERT_EQUAL(COL_CYAN, device->GetPixel(Point(0, 0)));
+            CPPUNIT_ASSERT_EQUAL(COL_CYAN, device->GetPixel(Point(9, 9)));
+            CPPUNIT_ASSERT_EQUAL(COL_CYAN, device->GetPixel(Point(5, 5)));
+            // Erase with transparent, check it's transparent.
+            device->SetBackground(Wallpaper(COL_TRANSPARENT));
+            device->Erase();
+            exportDevice("/tmp/12-07_erase.png", device);
+            CPPUNIT_ASSERT_EQUAL(sal_uInt8(255), device->GetPixel(Point(0, 0)).GetTransparency());
+            CPPUNIT_ASSERT_EQUAL(sal_uInt8(255), device->GetPixel(Point(9, 9)).GetTransparency());
+            CPPUNIT_ASSERT_EQUAL(sal_uInt8(255), device->GetPixel(Point(5, 5)).GetTransparency());
+        }
+    }
+
     void testTdf124848()
     {
         ScopedVclPtr<VirtualDevice> device = VclPtr<VirtualDevice>::Create(DeviceFormat::DEFAULT);
@@ -626,6 +691,8 @@ public:
 
     CPPUNIT_TEST(testDashedLine);
 
+    CPPUNIT_TEST(testErase);
+
     CPPUNIT_TEST(testTdf124848);
     CPPUNIT_TEST(testTdf136171);
 
diff --git a/vcl/source/outdev/outdevstate.cxx b/vcl/source/outdev/outdevstate.cxx
index 804ba883c210..4ab3093b573b 100644
--- a/vcl/source/outdev/outdevstate.cxx
+++ b/vcl/source/outdev/outdevstate.cxx
@@ -455,7 +455,44 @@ void OutputDevice::SetBackground( const Wallpaper& rBackground )
         mbBackground = true;
 
     if( mpAlphaVDev )
-        mpAlphaVDev->SetBackground( rBackground );
+    {
+        // Some of these are probably wrong (e.g. if the gradient has transparency),
+        // but hopefully nobody uses that. If you do, feel free to implement it properly.
+        if( rBackground.GetStyle() == WallpaperStyle::NONE )
+            mpAlphaVDev->SetBackground( rBackground );
+        else if( rBackground.IsBitmap())
+        {
+            BitmapEx bitmap = rBackground.GetBitmap();
+            if( bitmap.IsAlpha())
+                mpAlphaVDev->SetBackground( Wallpaper( BitmapEx( Bitmap( bitmap.GetAlpha()))));
+            else
+            {
+                switch( bitmap.GetTransparentType())
+                {
+                    case TransparentType::NONE:
+                        mpAlphaVDev->SetBackground( Wallpaper( COL_BLACK ));
+                        break;
+                    case TransparentType::Color:
+                    {
+                        AlphaMask mask( bitmap.GetBitmap().CreateMask( bitmap.GetTransparentColor()));
+                        mpAlphaVDev->SetBackground( Wallpaper( BitmapEx( bitmap.GetBitmap(), mask )));
+                        break;
+                    }
+                    case TransparentType::Bitmap:
+                        mpAlphaVDev->SetBackground( Wallpaper( BitmapEx( bitmap.GetMask())));
+                        break;
+                }
+            }
+        }
+        else if( rBackground.IsGradient())
+            mpAlphaVDev->SetBackground( Wallpaper( COL_BLACK ));
+        else
+        {
+            // Color background.
+            int transparency = rBackground.GetColor().GetTransparency();
+            mpAlphaVDev->SetBackground( Wallpaper( Color( transparency, transparency, transparency )));
+        }
+    }
 }
 
 void OutputDevice::SetFont( const vcl::Font& rNewFont )