Improve Paint.hasGlyph performance by caching hb_font_t

It turned out that hb_font_t creation is not a lightweight operation.
Especially, Paint.hasGlyph creates hb_font_t for all existing fonts
every time. To improve the performance, cache hb_font_t instead
of hb_face_t.

Note that to calculate horizontal advance, MinikinPaint needs to be
associated with hb_font_t by calling hb_font_set_funcs. With this patch,
hb_font_set_funcs may be called multiple times for the same hb_font_t
object. However this is not an issue since MinikinPaint is unique
during layout.

Bug: 26784699

Change-Id: I516498ae9f0127d700fc9829327e9789845a1416

2 files changed, 2 insertions, 12 deletions

diff --git a/include/minikin/FontCollection.h b/include/minikin/FontCollection.h
index 294692f..3a63c07 100644
--- a/include/minikin/FontCollection.h
+++ b/include/minikin/FontCollection.h
@@ -53,9 +53,6 @@ public:
 
     uint32_t getId() const;
 
-    // Calls each managed font family's FontFamily::purgeHbFontCache method.
-    // Caller should acquire a lock before calling the method.
-    void purgeFontFamilyHbFontCache() const;
 private:
     static const int kLogCharsPerPage = 8;
     static const int kPageMask = (1 << kLogCharsPerPage) - 1;
diff --git a/include/minikin/FontFamily.h b/include/minikin/FontFamily.h
index aa2e0ac..2b59160 100644
--- a/include/minikin/FontFamily.h
+++ b/include/minikin/FontFamily.h
@@ -100,11 +100,11 @@ struct FakedFont {
 
 class FontFamily : public MinikinRefCounted {
 public:
-    FontFamily() : mHbFont(nullptr) { }
+    FontFamily() {}
 
     FontFamily(int variant);
 
-    FontFamily(uint32_t langId, int variant) : mLangId(langId), mVariant(variant), mHbFont(nullptr) {
+    FontFamily(uint32_t langId, int variant) : mLangId(langId), mVariant(variant) {
     }
 
     ~FontFamily();
@@ -131,11 +131,6 @@ public:
     // Caller should acquire a lock before calling the method.
     bool hasVariationSelector(uint32_t codepoint, uint32_t variationSelector);
 
-    // Purges cached mHbFont.
-    // hb_font_t keeps a reference to hb_face_t which is managed by HbFaceCache. Thus,
-    // it is good to purge hb_font_t once it is no longer necessary.
-    // Caller should acquire a lock before calling the method.
-    void purgeHbFontCache();
 private:
     void addFontLocked(MinikinFont* typeface, FontStyle style);
 
@@ -152,8 +147,6 @@ private:
 
     SparseBitSet mCoverage;
     bool mCoverageValid;
-
-    hb_font_t* mHbFont;
 };
 
 }  // namespace android