LOK: Impress slide layers render on macOS

SlideshowLayerRenderer painted into the client's buffer, which Aqua
devices cannot do: every layer came back empty. On macOS paint into an
alpha device of its own and copy the pixels out, as tile painting does.

diff --git a/sd/source/ui/tools/SlideshowLayerRenderer.cxx b/sd/source/ui/tools/SlideshowLayerRenderer.cxx
index 8675630..7ecd4ad 100644
--- a/sd/source/ui/tools/SlideshowLayerRenderer.cxx
+++ b/sd/source/ui/tools/SlideshowLayerRenderer.cxx
@@ -23,6 +23,7 @@
 #include <svx/xflclit.hxx>
 #include <svx/xlnclit.hxx>
 
+#include <vcl/BitmapTools.hxx>
 #include <vcl/virdev.hxx>
 #include <tools/json_writer.hxx>
 #include <editeng/editeng.hxx>
@@ -87,6 +88,10 @@ private:
 
     EEControlBits mnSavedControlBits;
     Color maSavedBackgroundColor;
+#if defined(MACOSX)
+    unsigned char* mpBuffer;
+    Size maBufferSize;
+#endif
 
 public:
     ScopedVclPtrInstance<VirtualDevice> maVirtualDevice;
@@ -98,6 +103,10 @@ public:
         , maVirtualDevice(
               CoreGraphics::getiOSGraphicsData(pBuffer, rSlideSize.Width(), rSlideSize.Height()),
               Size(1, 1), DeviceFormat::WITHOUT_ALPHA)
+#elif defined(MACOSX)
+        , mpBuffer(pBuffer)
+        , maBufferSize(rSlideSize)
+        , maVirtualDevice(DeviceFormat::WITH_ALPHA)
 #else
         , maVirtualDevice(DeviceFormat::WITHOUT_ALPHA)
 #endif
@@ -114,8 +123,14 @@ public:
 
         maVirtualDevice->SetBackground(Wallpaper(COL_TRANSPARENT));
 
+#if defined(MACOSX)
+        // Aqua devices cannot paint client buffers: paint, then copy.
+        (void)rScale;
+        maVirtualDevice->SetOutputSizePixel(rSlideSize);
+#else
         maVirtualDevice->SetOutputSizePixelScaleOffsetAndLOKBuffer(rSlideSize, rScale, Point(),
                                                                    pBuffer);
+#endif
         Size aPageSize(rPage.GetSize());
 
         MapMode aMapMode(MapUnit::Map100thMM);
@@ -139,6 +154,11 @@ public:
 
 #ifdef IOS
         CoreGraphics::CGContextRelease(maVirtualDevice->GetSystemGfxData().rCGContext);
+#endif
+#if defined(MACOSX)
+        maVirtualDevice->EnableMapMode(false);
+        vcl::bitmap::fillWithData(mpBuffer,
+                                  maVirtualDevice->GetBitmap(Point(), maBufferSize));
 #endif
     }
 };