vcl: less text layout calls in ListBox

Number of GenericSalLayout::LayoutText() calls during Writer startup at
this call-site: 1068 -> 614.

Change-Id: I3bef56e550294a6b2c9fe73c0c6531249c9f1f30
Reviewed-on: https://gerrit.libreoffice.org/60164
Tested-by: Jenkins
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>

vcl/inc/listbox.hxx

@@ -23,6 +23,7 @@
 #include <vcl/button.hxx>
 #include <vcl/floatwin.hxx>
 #include <vcl/quickselectionengine.hxx>
+#include <vcl/vcllayout.hxx>
 
 #include <set>
 #include <vector>
@@ -45,6 +46,7 @@ enum LB_EVENT_TYPE
 struct ImplEntryType
 {
     OUString    maStr;
+    SalLayoutGlyphs maStrGlyphs;
     Image       maImage;
     void*       mpUserData;
     bool        mbIsSelected;
@@ -69,6 +71,9 @@ struct ImplEntryType
         mbIsSelected = false;
         mpUserData = nullptr;
     }
+
+    /// Computes maStr's text layout (glyphs), cached in maStrGlyphs.
+    SalLayoutGlyphs* GetTextGlyphs(OutputDevice* pOutputDevice);
 };
 
 class ImplEntryList

vcl/source/control/imp_listbox.cxx

@@ -601,6 +601,27 @@ struct ImplEntryMetrics
     long    nImgHeight;
 };
 
+SalLayoutGlyphs* ImplEntryType::GetTextGlyphs(OutputDevice* pOutputDevice)
+{
+    if (!maStrGlyphs.empty())
+        // Use pre-calculated result.
+        return &maStrGlyphs;
+
+    std::unique_ptr<SalLayout> pLayout = pOutputDevice->ImplLayout(
+        maStr, 0, maStr.getLength(), Point(0, 0), 0, nullptr, SalLayoutFlags::GlyphItemsOnly);
+    if (!pLayout)
+        return nullptr;
+
+    const SalLayoutGlyphs* pGlyphs = pLayout->GetGlyphs();
+    if (!pGlyphs)
+        return nullptr;
+
+    // Remember the calculation result.
+    maStrGlyphs = *pGlyphs;
+
+    return &maStrGlyphs;
+}
+
 void ImplListBoxWindow::EnableQuickSelection( bool b )
 {
     maQuickSelectionEngine.SetEnabled( b );
@@ -637,7 +658,9 @@ void ImplListBoxWindow::ImplUpdateEntryMetrics( ImplEntryType& rEntry )
         else
         {
             // normal single line case
-            aMetrics.nTextWidth = static_cast<sal_uInt16>(GetTextWidth( rEntry.maStr ));
+            const SalLayoutGlyphs* pGlyphs = rEntry.GetTextGlyphs(this);
+            aMetrics.nTextWidth
+                = static_cast<sal_uInt16>(GetTextWidth(rEntry.maStr, 0, -1, nullptr, pGlyphs));
             if( aMetrics.nTextWidth > mnMaxTxtWidth )
                 mnMaxTxtWidth = aMetrics.nTextWidth;
             aMetrics.nEntryWidth = mnMaxTxtWidth;