sidebar: allow panels to lurk around instead of being disposed.

Creating and destroying sidebar panels is done remarkably often - on
changes of context eg. The process is remarkably expensive - loading
UI XML files, processing them etc. and is un-necessary.

Instead let panels lurk around for future use - particularly in the
Properties deck which gets the most thrash. This gives a big speedup
particularly noticable on mobile where it could take several seconds
to load switch between panels for eg. shape vs. slide properties when
tapping to edit text.

Change-Id: I497e77432c11bbd1e35a8a8716519cabc3730e61
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/86233
Tested-by: Michael Meeks <michael.meeks@collabora.com>
Reviewed-by: Michael Meeks <michael.meeks@collabora.com>

4 files changed, 67 insertions, 41 deletions

diff --git a/sfx2/source/sidebar/Deck.cxx b/sfx2/source/sidebar/Deck.cxx
index fba9f1330833..074334c2e415 100644
--- a/sfx2/source/sidebar/Deck.cxx
+++ b/sfx2/source/sidebar/Deck.cxx
@@ -209,17 +209,25 @@ bool Deck::ProcessWheelEvent(CommandEvent const * pCommandEvent)
  */
 void Deck::ResetPanels(const SharedPanelContainer& rPanelContainer)
 {
-    // First dispose old panels we no longer need.
+    SharedPanelContainer aHiddens;
+
+    // First hide old panels we don't need just now.
     for (VclPtr<Panel> & rpPanel : maPanels)
     {
         bool bFound = false;
         for (const auto & i : rPanelContainer)
             bFound = bFound || (rpPanel.get() == i.get());
         if (!bFound) // this one didn't survive.
-            rpPanel.disposeAndClear();
+        {
+            rpPanel->SetLurkMode(true);
+            aHiddens.push_back(rpPanel);
+        }
     }
     maPanels = rPanelContainer;
 
+    // Hidden ones always at the end
+    maPanels.insert(std::end(maPanels), std::begin(aHiddens), std::end(aHiddens));
+
     RequestLayoutInternal();
 }
 
diff --git a/sfx2/source/sidebar/DeckLayouter.cxx b/sfx2/source/sidebar/DeckLayouter.cxx
index 0337c7cc46d6..33d6dc62f4b9 100644
--- a/sfx2/source/sidebar/DeckLayouter.cxx
+++ b/sfx2/source/sidebar/DeckLayouter.cxx
@@ -289,7 +289,7 @@ sal_Int32 PlacePanels (
             }
         }
 
-        if (rPanel.IsExpanded())
+        if (rPanel.IsExpanded() && !rPanel.IsLurking())
         {
             rPanel.Show();
 
@@ -353,46 +353,51 @@ void GetRequestedSizes (
 
     for (LayoutItem& item : rLayoutItems)
     {
-        ui::LayoutSize aLayoutSize (ui::LayoutSize(0,0,0));
-        if (item.mpPanel != nullptr)
+        item.maLayoutSize = ui::LayoutSize(0,0,0);
+
+        if (item.mpPanel == nullptr)
+            continue;
+
+        if (item.mpPanel->IsLurking())
         {
-            if (rLayoutItems.size() == 1
-                && item.mpPanel->IsTitleBarOptional())
-            {
-                // There is only one panel and its title bar is
-                // optional => hide it.
-                rAvailableHeight -= nDeckSeparatorHeight;
-                item.mbShowTitleBar = false;
-            }
-            else
-            {
-                // Show the title bar and a separator above and below
-                // the title bar.
-                const sal_Int32 nPanelTitleBarHeight(
-                    Theme::GetInteger(Theme::Int_PanelTitleBarHeight)
-                    * item.mpPanel->GetDPIScaleFactor());
-
-                rAvailableHeight -= nPanelTitleBarHeight;
-                rAvailableHeight -= nDeckSeparatorHeight;
-            }
+            item.mbShowTitleBar = false;
+            continue;
+        }
 
-            if (item.mpPanel->IsExpanded())
+        if (rLayoutItems.size() == 1
+            && item.mpPanel->IsTitleBarOptional())
+        {
+            // There is only one panel and its title bar is
+            // optional => hide it.
+            rAvailableHeight -= nDeckSeparatorHeight;
+            item.mbShowTitleBar = false;
+        }
+        else
+        {
+            // Show the title bar and a separator above and below
+            // the title bar.
+            const sal_Int32 nPanelTitleBarHeight(
+                Theme::GetInteger(Theme::Int_PanelTitleBarHeight)
+                * item.mpPanel->GetDPIScaleFactor());
+
+            rAvailableHeight -= nPanelTitleBarHeight;
+            rAvailableHeight -= nDeckSeparatorHeight;
+        }
+
+        if (item.mpPanel->IsExpanded())
+        {
+            Reference<ui::XSidebarPanel> xPanel(item.mpPanel->GetPanelComponent());
+            if (xPanel.is())
             {
-                Reference<ui::XSidebarPanel> xPanel(item.mpPanel->GetPanelComponent());
-                if (xPanel.is())
-                {
-                    aLayoutSize = xPanel->getHeightForWidth(rContentBox.GetWidth());
-
-                    const sal_Int32 nWidth = xPanel->getMinimalWidth();
-                    if (nWidth > rMinimalWidth)
-                        rMinimalWidth = nWidth;
-                }
-                else
-                    aLayoutSize = ui::LayoutSize(MinimalPanelHeight, -1, 0);
+                item.maLayoutSize = xPanel->getHeightForWidth(rContentBox.GetWidth());
+
+                const sal_Int32 nWidth = xPanel->getMinimalWidth();
+                if (nWidth > rMinimalWidth)
+                    rMinimalWidth = nWidth;
             }
+            else
+                item.maLayoutSize = ui::LayoutSize(MinimalPanelHeight, -1, 0);
         }
-
-        item.maLayoutSize = aLayoutSize;
     }
 }
 
diff --git a/sfx2/source/sidebar/Panel.cxx b/sfx2/source/sidebar/Panel.cxx
index 7968f667b92d..dc4ea895d26d 100644
--- a/sfx2/source/sidebar/Panel.cxx
+++ b/sfx2/source/sidebar/Panel.cxx
@@ -57,6 +57,7 @@ Panel::Panel(const PanelDescriptor& rPanelDescriptor,
     , mxElement()
     , mxPanelComponent()
     , mbIsExpanded(bIsInitiallyExpanded)
+    , mbLurking(false)
     , maDeckLayoutTrigger(rDeckLayoutTrigger)
     , maContextAccess(rContextAccess)
     , mxFrame(rxFrame)
@@ -70,6 +71,12 @@ Panel::~Panel()
     assert(!mpTitleBar);
 }
 
+void Panel::SetLurkMode(bool bLurk)
+{
+    // cf. DeckLayouter
+    mbLurking = bLurk;
+}
+
 void Panel::ApplySettings(vcl::RenderContext& rRenderContext)
 {
     rRenderContext.SetBackground(Theme::GetPaint(Theme::Paint_PanelBackground).GetWallpaper());
@@ -77,9 +84,14 @@ void Panel::ApplySettings(vcl::RenderContext& rRenderContext)
 
 boost::property_tree::ptree Panel::DumpAsPropertyTree()
 {
-    boost::property_tree::ptree aTree(vcl::Window::DumpAsPropertyTree());
-    aTree.put("type", "panel");
-    return aTree;
+    if (!IsLurking())
+    {
+        boost::property_tree::ptree aTree(vcl::Window::DumpAsPropertyTree());
+        aTree.put("type", "panel");
+        return aTree;
+    }
+    else
+        return boost::property_tree::ptree();
 }
 
 void Panel::dispose()
diff --git a/sfx2/source/sidebar/SidebarController.cxx b/sfx2/source/sidebar/SidebarController.cxx
index 91405791c727..f11ce95e7213 100644
--- a/sfx2/source/sidebar/SidebarController.cxx
+++ b/sfx2/source/sidebar/SidebarController.cxx
@@ -716,6 +716,7 @@ void SidebarController::CreatePanels(const OUString& rDeckId, const Context& rCo
         Panel *const pPanel(pDeck->GetPanel(rPanelContexDescriptor.msId));
         if (pPanel != nullptr)
         {
+            pPanel->SetLurkMode(false);
             aNewPanels[nWriteIndex] = pPanel;
             pPanel->SetExpanded( rPanelContexDescriptor.mbIsInitiallyVisible );
             ++nWriteIndex;