1 files changed, 35 insertions, 13 deletions

diff --git a/src/3rdparty/harfbuzz/src/harfbuzz-shaper.cpp b/src/3rdparty/harfbuzz/src/harfbuzz-shaper.cpp
index f6900325bc..e630ec3808 100644
--- a/src/3rdparty/harfbuzz/src/harfbuzz-shaper.cpp
+++ b/src/3rdparty/harfbuzz/src/harfbuzz-shaper.cpp
@@ -1302,30 +1302,52 @@ HB_Bool HB_OpenTypePosition(HB_ShaperItem *item, int availableGlyphs, HB_Bool do
         glyphs[i] = face->buffer->in_string[i].gindex;
         attributes[i] = face->tmpAttributes[face->buffer->in_string[i].cluster];
         if (i && face->buffer->in_string[i].cluster == face->buffer->in_string[i-1].cluster)
-            attributes[i].clusterStart = false;
+            attributes[i].clusterStart = false; //FIXME - Shouldn't we otherwise set this to true, rather than leaving it?
     }
     item->num_glyphs = face->buffer->in_length;
 
     if (doLogClusters && face->glyphs_substituted) {
         // we can't do this for indic, as we pass the stuf in syllables and it's easier to do it in the shaper.
-        unsigned short *logClusters = item->log_clusters;
-        int clusterStart = 0;
-        int oldCi = 0;
         // #### the reconstruction of the logclusters currently does not work if the original string
         // contains surrogate pairs
+
+        unsigned short *logClusters = item->log_clusters;
+        int clusterStart = 0;
+        int oldIntermediateIndex = 0;
+
+        // This code makes a mapping, logClusters, between the original utf16 string (item->string) and the final
+        // set of glyphs (in_string).
+        //
+        // The code sets the value of logClusters[i] to the index of in_string containing the glyph that will render
+        // item->string[i].
+        //
+        // This is complicated slightly because in_string[i].cluster is an index to an intermediate
+        // array of glyphs - the array that we were passed as the original value of item->glyphs.
+        // To map from the original string to the intermediate array of glyphs we have tmpLogClusters.
+        //
+        // So we have three groups of indexes:
+        //
+        // i,clusterStart = index to in_length, the final set of glyphs.  Also an index to attributes
+        // intermediateIndex = index to the glyphs originally passed in.
+        // stringIndex = index to item->string, the original string.
+
+        int stringIndex = 0;
+        // Iterate over the final set of glyphs...
         for (unsigned int i = 0; i < face->buffer->in_length; ++i) {
-            int ci = face->buffer->in_string[i].cluster;
-            //         DEBUG("   ci[%d] = %d mark=%d, cmb=%d, cs=%d",
-            //                i, ci, glyphAttributes[i].mark, glyphAttributes[i].combiningClass, glyphAttributes[i].clusterStart);
-            if (!attributes[i].mark && attributes[i].clusterStart && ci != oldCi) {
-                for (int j = oldCi; j < ci; j++)
-                    logClusters[j] = clusterStart;
+            // Get the index into the intermediate string for the start of the cluster of chars
+            int intermediateIndex = face->buffer->in_string[i].cluster;
+            if (intermediateIndex != oldIntermediateIndex) {
+                // We have found the end of the cluster of chars in the intermediate string
+                while (face->tmpLogClusters[stringIndex] < intermediateIndex) {
+                    logClusters[stringIndex++] = clusterStart;
+                }
                 clusterStart = i;
-                oldCi = ci;
+                oldIntermediateIndex = intermediateIndex;
             }
         }
-        for (int j = oldCi; j < face->length; j++)
-            logClusters[j] = clusterStart;
+        while (stringIndex < face->length) {
+            logClusters[stringIndex++] = clusterStart;
+        }
     }
 
     // calulate the advances for the shaped glyphs