Avoid copying of font table data

The hb_font_t object holds on to tables of font data, acquired through
the MinikinFont::GetTable interface, which is based on copying data
into caller-owned buffers. Now that we're caching lots of hb_font_t's,
the cost of these buffers is significant.

This patch moves to a different interface, inspired by HarfBuzz's
hb_reference_table API, where the font can provide a pointer to the
actual font data (which will often be mmap'ed, so it doesn't even
consume physical RAM).

Bug: 27860101
Change-Id: Id766ab16a8d342bf7322a90e076e801271d527d4

2 files changed, 23 insertions, 4 deletions

diff --git a/include/minikin/MinikinFont.h b/include/minikin/MinikinFont.h
index 5c0ab0f..0298235 100644
--- a/include/minikin/MinikinFont.h
+++ b/include/minikin/MinikinFont.h
@@ -94,6 +94,9 @@ struct MinikinRect {
 
 class MinikinFontFreeType;
 
+// Callback for freeing data
+typedef void (*MinikinDestroyFunc) (void* data);
+
 class MinikinFont : public MinikinRefCounted {
 public:
     virtual ~MinikinFont();
@@ -104,8 +107,23 @@ public:
     virtual void GetBounds(MinikinRect* bounds, uint32_t glyph_id,
         const MinikinPaint &paint) const = 0;
 
-    // If buf is NULL, just update size
-    virtual bool GetTable(uint32_t tag, uint8_t *buf, size_t *size) = 0;
+    virtual const void* GetTable(uint32_t tag, size_t* size, MinikinDestroyFunc* destroy) = 0;
+
+    // Override if font can provide access to raw data
+    virtual const void* GetFontData() const {
+        return nullptr;
+    }
+
+    // Override if font can provide access to raw data
+    virtual size_t GetFontSize() const {
+        return 0;
+    }
+
+    // Override if font can provide access to raw data.
+    // Returns index within OpenType collection
+    virtual int GetFontIndex() const {
+        return 0;
+    }
 
     virtual int32_t GetUniqueId() const = 0;
 
diff --git a/include/minikin/MinikinFontFreeType.h b/include/minikin/MinikinFontFreeType.h
index a957d12..535c249 100644
--- a/include/minikin/MinikinFontFreeType.h
+++ b/include/minikin/MinikinFontFreeType.h
@@ -48,8 +48,9 @@ public:
     void GetBounds(MinikinRect* bounds, uint32_t glyph_id,
         const MinikinPaint& paint) const;
 
-    // If buf is NULL, just update size
-    bool GetTable(uint32_t tag, uint8_t *buf, size_t *size);
+    const void* GetTable(uint32_t tag, size_t* size, MinikinDestroyFunc* destroy);
+
+    // TODO: provide access to raw data, as an optimization.
 
     int32_t GetUniqueId() const;