tdf#108608 more Draw text editing responsiveness fixes

Turns out Windows is rather slow at at calculating glyph outlines
(compared to Linux), I'm guessing it does no caching at all, so
just add our own little cache.

I tried to use o3tl::lru_map here, but it crashes under MSVC2015.

Change-Id: I78d2a787ec8f734fa821f41f13236771efa1c8d4
Reviewed-on: https://gerrit.libreoffice.org/52623
Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

2 files changed, 24 insertions, 0 deletions

diff --git a/include/o3tl/lru_map.hxx b/include/o3tl/lru_map.hxx
index 2f41521795fc..4eb05bd97a43 100644
--- a/include/o3tl/lru_map.hxx
+++ b/include/o3tl/lru_map.hxx
@@ -132,6 +132,11 @@ public:
     {
         return mLruList.size();
     }
+
+    void clear()
+    {
+        mLruList.clear();
+    }
 };
 
 }
diff --git a/vcl/win/gdi/salfont.cxx b/vcl/win/gdi/salfont.cxx
index 9dbde8fd52d7..e415ec8fa1b3 100644
--- a/vcl/win/gdi/salfont.cxx
+++ b/vcl/win/gdi/salfont.cxx
@@ -56,6 +56,11 @@
 
 using namespace vcl;
 
+// GetGlyphOutlineW() seems to be a little slow, and doesn't seem to do it's own caching (tested on Windows10).
+// TODO use something a little smarter here like an LRU cache, and include the font as part of the cache key
+// The cache limit is set by the rough number of characters needed to read your average Asian newspaper.
+constexpr size_t BOUND_RECT_CACHE_SIZE = 3000;
+static std::unordered_map<sal_GlyphId, tools::Rectangle> g_BoundRectCache;
 
 inline FIXED FixedFromDouble( double d )
 {
@@ -835,6 +840,9 @@ void ImplGetLogFontFromFontSelect( HDC hDC,
 
 HFONT WinSalGraphics::ImplDoSetFont(FontSelectPattern const * i_pFont, HFONT& o_rOldFont)
 {
+    // clear the cache on font change
+    g_BoundRectCache.clear();
+
     HFONT hNewFont = nullptr;
 
     HDC hdcScreen = nullptr;
@@ -1326,6 +1334,15 @@ void WinSalGraphics::ClearDevFontCache()
 
 bool WinSalGraphics::GetGlyphBoundRect(const GlyphItem& rGlyph, tools::Rectangle& rRect)
 {
+    auto it = g_BoundRectCache.find(rGlyph.maGlyphId);
+    if (it != g_BoundRectCache.end())
+    {
+        rRect = it->second;
+        return true;
+    }
+    if (g_BoundRectCache.size() > BOUND_RECT_CACHE_SIZE)
+        g_BoundRectCache.clear();
+
     HDC hDC = getHDC();
 
     // use unity matrix
@@ -1347,6 +1364,8 @@ bool WinSalGraphics::GetGlyphBoundRect(const GlyphItem& rGlyph, tools::Rectangle
         Size( aGM.gmBlackBoxX, aGM.gmBlackBoxY ) );
     rRect.AdjustRight(1);
     rRect.AdjustBottom(1);
+
+    g_BoundRectCache.insert({rGlyph.maGlyphId, rRect});
     return true;
 }