Disable certain GPOS features by default

According to OpenType Layout tag registry, these features should be
turned off by default. Leaving them on will cause some text layout
problems in common UI widgets -- they are usually designed for better
positioning in print publishing or full featured text layout programs,
not for general usage.

There is no way to turn them on in HarfBuzz now, it should be
addressed later. Features like 'valt' are intended for vertical
writing mode are also turned off, since HarfBuzz doesn't support it
properly yet.

Task-number: QTBUG-15754
Reviewed-by: Lars Knoll

1 files changed, 35 insertions, 6 deletions

diff --git a/src/3rdparty/harfbuzz/src/harfbuzz-shaper.cpp b/src/3rdparty/harfbuzz/src/harfbuzz-shaper.cpp
index ce4d4ac..ef86144 100644
--- a/src/3rdparty/harfbuzz/src/harfbuzz-shaper.cpp
+++ b/src/3rdparty/harfbuzz/src/harfbuzz-shaper.cpp
@@ -538,8 +538,20 @@ void HB_HeuristicSetGlyphAttributes(HB_ShaperItem *item)
 #ifndef NO_OPENTYPE
 static const HB_OpenTypeFeature basic_features[] = {
     { HB_MAKE_TAG('c', 'c', 'm', 'p'), CcmpProperty },
-    { HB_MAKE_TAG('l', 'i', 'g', 'a'), CcmpProperty },
-    { HB_MAKE_TAG('c', 'l', 'i', 'g'), CcmpProperty },
+    { HB_MAKE_TAG('l', 'i', 'g', 'a'), LigaProperty },
+    { HB_MAKE_TAG('c', 'l', 'i', 'g'), CligProperty },
+    {0, 0}
+};
+
+static const HB_OpenTypeFeature disabled_features[] = {
+    { HB_MAKE_TAG('c', 'p', 'c', 't'), PositioningProperties },
+    { HB_MAKE_TAG('h', 'a', 'l', 't'), PositioningProperties },
+    // TODO: we need to add certain HB_ShaperFlag for vertical
+    // writing mode to enable these vertical writing features:
+    { HB_MAKE_TAG('v', 'a', 'l', 't'), PositioningProperties },
+    { HB_MAKE_TAG('v', 'h', 'a', 'l'), PositioningProperties },
+    { HB_MAKE_TAG('v', 'k', 'r', 'n'), PositioningProperties },
+    { HB_MAKE_TAG('v', 'p', 'a', 'l'), PositioningProperties },
     {0, 0}
 };
 #endif
@@ -1110,12 +1122,29 @@ HB_Bool HB_SelectScript(HB_ShaperItem *shaper_item, const HB_OpenTypeFeature *fe
                 HB_UInt *feature_tag_list = feature_tag_list_buffer;
                 while (*feature_tag_list) {
                     HB_UShort feature_index;
+                    bool skip = false;
                     if (*feature_tag_list == HB_MAKE_TAG('k', 'e', 'r', 'n')) {
-                        if (face->current_flags & HB_ShaperFlag_NoKerning) {
-                            ++feature_tag_list;
-                            continue;
+                        if (face->current_flags & HB_ShaperFlag_NoKerning)
+                            skip = true;
+                        else
+                            face->has_opentype_kerning = true;
+                    }
+                    features = disabled_features;
+                    while (features->tag) {
+                        if (*feature_tag_list == features->tag) {
+                            skip = true;
+                            break;
                         }
-                        face->has_opentype_kerning = true;
+                        ++features;
+                    }
+                    // 'palt' should be turned off by default unless 'kern' is on
+                    if (!face->has_opentype_kerning &&
+                        *feature_tag_list == HB_MAKE_TAG('p', 'a', 'l', 't'))
+                        skip = true;
+
+                    if (skip) {
+                        ++feature_tag_list;
+                        continue;
                     }
                     error = HB_GPOS_Select_Feature(face->gpos, *feature_tag_list, script_index, 0xffff, &feature_index);
                     if (!error)