avoid Xlib cairo surfaces for small virtual devices (bsc#1183308)

The (private :( ) document contains a large number of small shapes
for which VclProcessor2D::RenderTransparencePrimitive2D() gets
called, which results in GetBitmapEx() on the VirtualDevice.
And Cairo normally needs to do a roundtrip to the XServer to fetch
the content, which makes the rendering pretty slow. Forcing
image-based surface for small sizes of VirtualDevice actually has
better performance for the document, and the lack of possible
HW acceleration generally shouldn't matter for a surface this small.

Additionally drawinglayer's VirtualDevice reusing tries to reuse
even a large one when a small one is needed, so a hack is needed
to avoid that in this case, I couldn't find a better way.

Change-Id: I0f58659ab88165a6bd915f100fc3b1d4802a0fa9
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/128309
Tested-by: Jenkins
Reviewed-by: Luboš Luňák <l.lunak@collabora.com>
(cherry picked from commit cf9be3417bc2be5f772c03180b7cbd248b82cad5)
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/128815
Reviewed-by: Caolán McNamara <caolanm@redhat.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/vcl/source/outdev/outdev.cxx b/vcl/source/outdev/outdev.cxx
index 1083ff9b0d04..9231f7779a6b 100644
--- a/vcl/source/outdev/outdev.cxx
+++ b/vcl/source/outdev/outdev.cxx
@@ -230,6 +230,15 @@ SystemGraphicsData OutputDevice::GetSystemGfxData() const
     return mpGraphics->GetGraphicsData();
 }
 
+OUString OutputDevice::GetRenderBackendName() const
+{
+    if (!mpGraphics && !AcquireGraphics())
+        return {};
+    assert(mpGraphics);
+
+    return mpGraphics->getRenderBackendName();
+}
+
 #if ENABLE_CAIRO_CANVAS
 
 bool OutputDevice::SupportsCairo() const