Fixed text shaping bugs with ligatures and multiple font engines.

If Harfbuzz shaping adds or merges glyphs we need to move the remaining
glyphs in the glyph layout to compensate.

Task-number: 253783
Reviewed-by: Simon Hausmann

1 files changed, 26 insertions, 14 deletions

diff --git a/src/gui/text/qtextengine.cpp b/src/gui/text/qtextengine.cpp
index 80a5425790..da1ab25fc1 100644
--- a/src/gui/text/qtextengine.cpp
+++ b/src/gui/text/qtextengine.cpp
@@ -1099,6 +1099,16 @@ void QTextEngine::shapeTextWithCE(int item) const
 }
 #endif
 
+static inline void moveGlyphData(const QGlyphLayout &destination, const QGlyphLayout &source, int num)
+{
+    if (num > 0 && destination.glyphs != source.glyphs) {
+        memmove(destination.glyphs, source.glyphs, num * sizeof(HB_Glyph));
+        memmove(destination.attributes, source.attributes, num * sizeof(HB_GlyphAttributes));
+        memmove(destination.advances_x, source.advances_x, num * sizeof(HB_Fixed));
+        memmove(destination.offsets, source.offsets, num * sizeof(HB_FixedPoint));
+    }
+}
+
 /// take the item from layoutData->items and
 void QTextEngine::shapeTextWithHarfbuzz(int item) const
 {
@@ -1189,7 +1199,7 @@ void QTextEngine::shapeTextWithHarfbuzz(int item) const
 
 
 
-    int initial_glyph_pos = 0;
+    int remaining_glyphs = entire_shaper_item.num_glyphs;
     int glyph_pos = 0;
     // for each item shape using harfbuzz and store the results in our layoutData's glyphs array.
     for (int k = 0; k < itemBoundaries.size(); k += 2) { // for the +2, see the comment at the definition of itemBoundaries
@@ -1209,7 +1219,7 @@ void QTextEngine::shapeTextWithHarfbuzz(int item) const
         QFontEngine *actualFontEngine = font;
         uint engineIdx = 0;
         if (font->type() == QFontEngine::Multi) {
-            engineIdx = uint(initialGlyphs.glyphs[itemBoundaries[k + 1]] >> 24);
+            engineIdx = uint(initialGlyphs.glyphs[glyph_pos] >> 24);
 
             actualFontEngine = static_cast<QFontEngineMulti *>(font)->engine(engineIdx);
         }
@@ -1219,16 +1229,18 @@ void QTextEngine::shapeTextWithHarfbuzz(int item) const
 
         shaper_item.glyphIndicesPresent = true;
 
+        remaining_glyphs -= shaper_item.initialGlyphCount;
+
         do {
-            ensureSpace(glyph_pos + shaper_item.num_glyphs);
-            initialGlyphs = availableGlyphs(&si).mid(0, entire_shaper_item.num_glyphs);
-            shaper_item.num_glyphs = layoutData->glyphLayout.numGlyphs - layoutData->used - glyph_pos;
+            ensureSpace(glyph_pos + shaper_item.num_glyphs + remaining_glyphs);
 
-            const QGlyphLayout g = availableGlyphs(&si);
-            shaper_item.glyphs = g.glyphs + glyph_pos;
-            shaper_item.attributes = g.attributes + glyph_pos;
-            shaper_item.advances = reinterpret_cast<HB_Fixed *>(g.advances_x + glyph_pos);
-            shaper_item.offsets = reinterpret_cast<HB_FixedPoint *>(g.offsets + glyph_pos);
+            const QGlyphLayout g = availableGlyphs(&si).mid(glyph_pos);
+            moveGlyphData(g.mid(shaper_item.num_glyphs), g.mid(shaper_item.initialGlyphCount), remaining_glyphs);
+
+            shaper_item.glyphs = g.glyphs;
+            shaper_item.attributes = g.attributes;
+            shaper_item.advances = reinterpret_cast<HB_Fixed *>(g.advances_x);
+            shaper_item.offsets = reinterpret_cast<HB_FixedPoint *>(g.offsets);
 
             if (shaper_item.glyphIndicesPresent) {
                 for (hb_uint32 i = 0; i < shaper_item.initialGlyphCount; ++i)
@@ -1241,18 +1253,18 @@ void QTextEngine::shapeTextWithHarfbuzz(int item) const
         } while (!qShapeItem(&shaper_item)); // this does the actual shaping via harfbuzz.
 
         QGlyphLayout g = availableGlyphs(&si).mid(glyph_pos, shaper_item.num_glyphs);
+        moveGlyphData(g.mid(shaper_item.num_glyphs), g.mid(shaper_item.initialGlyphCount), remaining_glyphs);
 
-        for (hb_uint32 i = 0; i < shaper_item.item.length; ++i) {
+        for (hb_uint32 i = 0; i < shaper_item.num_glyphs; ++i)
             g.glyphs[i] = g.glyphs[i] | (engineIdx << 24);
+
+        for (hb_uint32 i = 0; i < shaper_item.item.length; ++i)
             shaper_item.log_clusters[i] += glyph_pos;
-        }
 
         if (kerningEnabled && !shaper_item.kerning_applied)
             font->doKerning(&g, option.useDesignMetrics() ? QFlag(QTextEngine::DesignMetrics) : QFlag(0));
 
         glyph_pos += shaper_item.num_glyphs;
-
-        initial_glyph_pos += shaper_item.initialGlyphCount;
     }
 
 //     qDebug("    -> item: script=%d num_glyphs=%d", shaper_item.script, shaper_item.num_glyphs);