Make cache of opentype tables in Harfbuzz face lazy

The mechanism in fontconfig which determines if a certain character
is available (FcCharSetHasChar()) may give false positives, in which
case we would load and unload those fonts per every char for which
FC gave us a false positive. This was a major performance regression.
Specifically the false positives happened when looking at e.g.
italic variants of certain multilingual fonts, since we only check
the charset of the font family as a whole and not of the specific variant,
which may only support a subset of the chars.

To optimize this, we remove the deletion of the font engines after
loading them, but also wait with loading the opentype tables until
they are actually needed. This means that for the false positives,
we will load the font, but the cached data for each unused font will
be much smaller.

Change-Id: Idfc794401a2080da5946bf65204eb947aeb635ed
Reviewed-by: Lars Knoll <lars.knoll@nokia.com>

2 files changed, 32 insertions, 2 deletions

diff --git a/src/3rdparty/harfbuzz/src/harfbuzz-shaper.cpp b/src/3rdparty/harfbuzz/src/harfbuzz-shaper.cpp
index af0ee52e9a..f6900325bc 100644
--- a/src/3rdparty/harfbuzz/src/harfbuzz-shaper.cpp
+++ b/src/3rdparty/harfbuzz/src/harfbuzz-shaper.cpp
@@ -995,7 +995,7 @@ static HB_Stream getTableStream(void *font, HB_GetFontTableFunc tableFunc, HB_Ta
     return stream;
 }
 
-HB_Face HB_NewFace(void *font, HB_GetFontTableFunc tableFunc)
+HB_Face HB_AllocFace(void *font, HB_GetFontTableFunc tableFunc)
 {
     HB_Face face = (HB_Face )malloc(sizeof(HB_FaceRec));
     if (!face)
@@ -1012,6 +1012,30 @@ HB_Face HB_NewFace(void *font, HB_GetFontTableFunc tableFunc)
     face->tmpLogClusters = 0;
     face->glyphs_substituted = false;
     face->buffer = 0;
+    face->font_for_init = font;
+    face->get_font_table_func = tableFunc;
+
+    return face;
+}
+
+HB_Face HB_NewFace(void *font, HB_GetFontTableFunc tableFunc)
+{
+    HB_Face face = HB_AllocFace(font, tableFunc);
+    if (face)
+        face = HB_LoadFace(face);
+    return face;
+}
+
+HB_Face HB_LoadFace(HB_Face face)
+{
+    void *font = face->font_for_init;
+    if (!font)
+        return face;
+
+    HB_GetFontTableFunc tableFunc = face->get_font_table_func;
+
+    face->get_font_table_func = 0;
+    face->font_for_init = 0;
 
     HB_Error error = HB_Err_Ok;
     HB_Stream stream;
diff --git a/src/3rdparty/harfbuzz/src/harfbuzz-shaper.h b/src/3rdparty/harfbuzz/src/harfbuzz-shaper.h
index 470e27b6f9..f225a86525 100644
--- a/src/3rdparty/harfbuzz/src/harfbuzz-shaper.h
+++ b/src/3rdparty/harfbuzz/src/harfbuzz-shaper.h
@@ -201,6 +201,8 @@ typedef struct {
     hb_bitfield combiningClass  :8;
 } HB_GlyphAttributes;
 
+typedef HB_Error (*HB_GetFontTableFunc)(void *font, HB_Tag tag, HB_Byte *buffer, HB_UInt *length);
+
 typedef struct HB_FaceRec_ {
     HB_Bool isSymbolFont;
 
@@ -217,11 +219,15 @@ typedef struct HB_FaceRec_ {
     unsigned int *tmpLogClusters;
     int length;
     int orig_nglyphs;
+    void *font_for_init;
+    HB_GetFontTableFunc get_font_table_func;
 } HB_FaceRec;
 
-typedef HB_Error (*HB_GetFontTableFunc)(void *font, HB_Tag tag, HB_Byte *buffer, HB_UInt *length);
+
 
 HB_Face HB_NewFace(void *font, HB_GetFontTableFunc tableFunc);
+HB_Face HB_AllocFace(void *font, HB_GetFontTableFunc tableFunc);
+HB_Face HB_LoadFace(HB_Face face);
 void HB_FreeFace(HB_Face face);
 
 typedef struct {