make VirtualDevice::SetOutputSizePixelScaleOffsetAndBuffer() LOK-only

Because it's used only for LOK, and SvpSalVirtualDevice::CreateSurface()
otherwise wouldn't know whether to apply LOK DPI settings or not
(since this might be called for LOK tiled painting, when it should,
or it might be called from somewhere else while LOK is active, in which
case this should be handled normally). Getting that mismatched can cause
things like https://github.com/CollaboraOnline/online/issues/4834 .

Change-Id: I1df7b8a169c8ef2e799731a6695a032948536582
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/135588
Tested-by: Jenkins
Reviewed-by: Luboš Luňák <l.lunak@collabora.com>
(cherry picked from commit 91b98efc2a5cf41d9442f90d7cb37075721519e0)
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/135710

2 files changed, 21 insertions, 22 deletions

diff --git a/vcl/headless/svpvd.cxx b/vcl/headless/svpvd.cxx
index 76cb53fc1745..162bd78ec75a 100644
--- a/vcl/headless/svpvd.cxx
+++ b/vcl/headless/svpvd.cxx
@@ -76,28 +76,24 @@ void SvpSalVirtualDevice::CreateSurface(tools::Long nNewDX, tools::Long nNewDY,
         cairo_surface_destroy(m_pSurface);
     }
 
-    double fXScale, fYScale;
-    if (comphelper::LibreOfficeKit::isActive())
-    {
-        // Force scaling of the painting
-        fXScale = fYScale = comphelper::LibreOfficeKit::getDPIScale();
-    }
-    else
-    {
-        dl_cairo_surface_get_device_scale(m_pRefSurface, &fXScale, &fYScale);
-    }
-
     if (pBuffer)
     {
-        nNewDX *= fXScale;
-        nNewDY *= fYScale;
+        // The buffer should only be set by VirtualDevice::SetOutputSizePixelScaleOffsetAndLOKBuffer()
+        // when used to draw a tile for LOK. It cannot be used for something else, because otherwise
+        // this would need a way to detect whether this is a tiled paint that needs LOK handling
+        // or whether it's that something else that just might happen to be called with LOK active.
+        assert(comphelper::LibreOfficeKit::isActive());
+        // Force scaling of the painting
+        double fScale = comphelper::LibreOfficeKit::getDPIScale();
 
         m_pSurface = cairo_image_surface_create_for_data(pBuffer, CAIRO_FORMAT_ARGB32,
                             nNewDX, nNewDY, cairo_format_stride_for_width(CAIRO_FORMAT_ARGB32, nNewDX));
-        dl_cairo_surface_set_device_scale(m_pSurface, fXScale, fYScale);
+        dl_cairo_surface_set_device_scale(m_pSurface, fScale, fScale);
     }
     else if(nNewDX <= 32 && nNewDY <= 32)
     {
+        double fXScale, fYScale;
+        dl_cairo_surface_get_device_scale(m_pRefSurface, &fXScale, &fYScale);
         nNewDX *= fXScale;
         nNewDY *= fYScale;
 
diff --git a/vcl/source/gdi/virdev.cxx b/vcl/source/gdi/virdev.cxx
index 1aec06239913..e082e4b21e72 100644
--- a/vcl/source/gdi/virdev.cxx
+++ b/vcl/source/gdi/virdev.cxx
@@ -19,6 +19,7 @@
 
 #include <sal/config.h>
 
+#include <comphelper/lok.hxx>
 #include <sal/log.hxx>
 #include <tools/debug.hxx>
 
@@ -409,17 +410,19 @@ bool VirtualDevice::SetOutputSizePixel( const Size& rNewSize, bool bErase )
     return ImplSetOutputSizePixel(rNewSize, bErase, nullptr);
 }
 
-bool VirtualDevice::SetOutputSizePixelScaleOffsetAndBuffer(
+bool VirtualDevice::SetOutputSizePixelScaleOffsetAndLOKBuffer(
     const Size& rNewSize, const Fraction& rScale, const Point& rNewOffset,
     sal_uInt8 *const pBuffer)
 {
-    if (pBuffer) {
-        MapMode mm = GetMapMode();
-        mm.SetOrigin( rNewOffset );
-        mm.SetScaleX( rScale );
-        mm.SetScaleY( rScale );
-        SetMapMode( mm );
-    }
+    // If this is ever needed for something else than LOK, changes will
+    // be needed in SvpSalVirtualDevice::CreateSurface() .
+    assert(comphelper::LibreOfficeKit::isActive());
+    assert(pBuffer);
+    MapMode mm = GetMapMode();
+    mm.SetOrigin( rNewOffset );
+    mm.SetScaleX( rScale );
+    mm.SetScaleY( rScale );
+    SetMapMode( mm );
     return ImplSetOutputSizePixel(rNewSize, true, pBuffer);
 }