Access font tables in memory

third_party/WebKit/Source/platform/fonts/shaping/HarfBuzzFace.cpp

Index: third_party/WebKit/Source/platform/fonts/shaping/HarfBuzzFace.cpp
diff --git a/third_party/WebKit/Source/platform/fonts/shaping/HarfBuzzFace.cpp b/third_party/WebKit/Source/platform/fonts/shaping/HarfBuzzFace.cpp
index 3dffa865fa78be278de638b8fbc22ff511942c9c..5e8378f4d5892874359e718e414a681817912d25 100644
--- a/third_party/WebKit/Source/platform/fonts/shaping/HarfBuzzFace.cpp
+++ b/third_party/WebKit/Source/platform/fonts/shaping/HarfBuzzFace.cpp
@@ -50,6 +50,7 @@
 #include <SkPath.h>
 #include <SkPoint.h>
 #include <SkRect.h>
+#include <SkStream.h>
 #include <SkTypeface.h>
 
 
@@ -311,12 +312,36 @@ static hb_blob_t* harfBuzzSkiaGetTable(hb_face_t* face, hb_tag_t tag, void* user
 }
 #endif
 
+#if !OS(MACOSX)
+static void deleteTypefaceStream(void* streamAssetPtr)
+{
+    SkStreamAsset* streamAsset = reinterpret_cast<SkStreamAsset*>(streamAssetPtr);
+    delete streamAsset;
+}
+#endif
+
 hb_face_t* HarfBuzzFace::createFace()
 {
 #if OS(MACOSX)
     hb_face_t* face = hb_coretext_face_create(m_platformData->cgFont());
 #else
-    hb_face_t* face = hb_face_create_for_tables(harfBuzzSkiaGetTable, m_platformData->typeface(), 0);
+    hb_face_t* face = nullptr;
+
+    SkTypeface* typeface = m_platformData->typeface();
+    SkStreamAsset* typefaceStream = typeface->openStream(0);
+    if (typefaceStream->getMemoryBase()) {
+        std::unique_ptr<hb_blob_t, void(*)(hb_blob_t*)> faceBlob(hb_blob_create(
+            reinterpret_cast<const char*>(typefaceStream->getMemoryBase()),

[Ilya Kulshin, 2016/06/21 15:43:42]

I'm not familiar with how harfbuzz handles object lifetime, but I wanted to
point out that the pointer returned from getMemoryBase is only valid as long as
the underlying SkDWriteFontFileStream remains alive. If there's any chance that
memory might be used after the SkStreamAsset is destroyed, it's worth
doublechecking.

[drott, 2016/06/22 07:19:48]

Thanks for pointing that out. The hb_face_create() call references the
hb_blobt_t and keeps it alive until the hb_face_t itself gets destroyed. Then,
the destruction function deleteTypeFaceStream is called, which destroys the
SkStreamAsset. So the lifetime of the SkStreamAsset is coupled to the hb_face_t.
So, as long as we have a FontPlatformData (with an SkTypeface member) we have a
HarfBuzzFace, which has the hb_font_t, which keeps the hb_face_t. So, it looks
to me like the lifecycle of the SkStreamAsset is sound.

+            typefaceStream->getLength(),
+            HB_MEMORY_MODE_READONLY,
+            typefaceStream,
+            deleteTypefaceStream),
+            hb_blob_destroy);
+        face = hb_face_create(faceBlob.get(), 0);
+    }
+
+    // Fallback to table copies if there is no in-memory access.
+    face = hb_face_create_for_tables(harfBuzzSkiaGetTable, m_platformData->typeface(), 0);

[Ilya Kulshin, 2016/06/21 15:43:42]

Doesn't this always overwrite |face| and ignore the result of the new code?

[drott, 2016/06/22 07:19:48]

Oups, yes, my bad. There was an "if (face)" in my first version and I
"simplified" that away. 

 #endif
     ASSERT(face);
     return face;