tdf#138010 (IV) VclScrolledWindow: Use actual border width

The frame drawn by 'DecorationView::DrawFrame' may
use native drawing, in which case the frame may be wider
than 1 pixel.

Take that into account and calculate the frame width
and resulting position/size of the scrollbars and
child widget using the content rectangle returned when
drawing the frame using 'DecorationView::DrawFrame'.

This avoids that the child widget is drawn on top
of the frame, which e.g. resulted in no visible border
when using the Qt/KDE Breeze style, which has a frame
width of 2, with the actual 1 pixel border being
surrounded by a 1 pixel padding/margin, and the content
being drawn on top of the 1 pixel border. With the
child widget being drawn on top of the actual border,
only the invisible padding was left where a visible
border was expected.

(The current implementation assumes that the same frame
width is used on all sides, which matches the
way Qt styles handle it, but could be further extended
if necessary.)

Change-Id: I44268728838406fc578774c0f4fcc167fb2798b5
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/106157
Tested-by: Jenkins
Reviewed-by: Michael Weghorn <m.weghorn@posteo.de>

1 files changed, 19 insertions, 4 deletions

diff --git a/vcl/source/window/layout.cxx b/vcl/source/window/layout.cxx
index 9069d1aa7132..9b562c340b6b 100644
--- a/vcl/source/window/layout.cxx
+++ b/vcl/source/window/layout.cxx
@@ -1803,11 +1803,10 @@ IMPL_LINK( VclExpander, ClickHdl, CheckBox&, rBtn, void )
     maExpandedHdl.Call(*this);
 }
 
-const tools::Long VclScrolledWindow::m_nBorderWidth = 1;
-
 VclScrolledWindow::VclScrolledWindow(vcl::Window *pParent)
     : VclBin(pParent, WB_HIDE | WB_CLIPCHILDREN | WB_AUTOHSCROLL | WB_AUTOVSCROLL | WB_TABSTOP)
     , m_bUserManagedScrolling(false)
+    , m_nBorderWidth(1)
     , m_eDrawFrameStyle(DrawFrameStyle::NONE)
     , m_eDrawFrameFlags(DrawFrameFlags::NONE)
     , m_pVScroll(VclPtr<ScrollBar>::Create(this, WB_HIDE | WB_VERT))
@@ -2068,11 +2067,27 @@ bool VclScrolledWindow::EventNotify(NotifyEvent& rNEvt)
     return bDone || VclBin::EventNotify( rNEvt );
 }
 
+void VclScrolledWindow::updateBorderWidth(tools::Long nBorderWidth)
+{
+    if (m_nBorderWidth == nBorderWidth || nBorderWidth < 1)
+        return;
+
+    m_nBorderWidth = nBorderWidth;
+    // update scrollbars and child window
+    doSetAllocation(GetSizePixel(), false);
+};
+
 void VclScrolledWindow::Paint(vcl::RenderContext& rRenderContext, const tools::Rectangle& rRect)
 {
-    VclBin::Paint(rRenderContext, rRect);
+    const tools::Rectangle aRect(tools::Rectangle(Point(0,0), GetSizePixel()));
     DecorationView aDecoView(&rRenderContext);
-    aDecoView.DrawFrame(tools::Rectangle(Point(0,0), GetSizePixel()), m_eDrawFrameStyle, m_eDrawFrameFlags);
+    const tools::Rectangle aContentRect = aDecoView.DrawFrame(aRect, m_eDrawFrameStyle, m_eDrawFrameFlags);
+
+    // take potentially changed frame size into account before rendering content
+    const tools::Long nFrameWidth = (aRect.GetWidth() - aContentRect.GetWidth()) / 2;
+    updateBorderWidth(nFrameWidth);
+
+    VclBin::Paint(rRenderContext, rRect);
 }
 
 void VclViewport::setAllocation(const Size &rAllocation)