[[ Bug 18132 ]] Fix cluster computation for non-monotonic lines

runrevmark · runrevmark · commit 5626ee68ba03 · 2016-09-02T15:58:58.000+01:00
CoreText can generate runs which reference chars in the string
'out of order' for certain unicode strings (the case which gave
rise to the bug is from gujarati).

This patch ensures that reasonable cluster information is always
generated by ignoring the char range fetched from a CTRun, and
computing it as the min/max indices in the string index array
fetched from a CTRun.
diff --git a/docs/notes/bugfix-18132.md b/docs/notes/bugfix-18132.md
@@ -0,0 +1 @@
+# Ensure complex unicode scripts render correctly to PDF.
diff --git a/engine/src/coretextlayout.mm b/engine/src/coretextlayout.mm
@@ -157,22 +157,34 @@ bool MCTextLayout(const unichar_t *p_chars, uint32_t p_char_count, MCFontStruct
 			CTRunRef t_run;
 			t_run = (CTRunRef)t_run_id;
 			
-			uint32_t t_glyph_count;
+			CFIndex t_glyph_count;
 			t_glyph_count = CTRunGetGlyphCount(t_run);
 			
-			CFRange t_char_range;
-			t_char_range = CTRunGetStringRange(t_run);
-			
 			CGGlyph *t_glyphs;
 			CGPoint *t_positions;
 			CFIndex *t_indices;
 			t_glyphs = new CGGlyph[t_glyph_count];
 			t_positions = new CGPoint[t_glyph_count];
 			t_indices = new CFIndex[t_glyph_count];
-			CTRunGetGlyphs(t_run, CFRangeMake(0, 0), t_glyphs);
-			CTRunGetPositions(t_run, CFRangeMake(0, 0), t_positions);
-			CTRunGetStringIndices(t_run, CFRangeMake(0, 0), t_indices);
+			CTRunGetGlyphs(t_run, CFRangeMake(0, t_glyph_count), t_glyphs);
+			CTRunGetPositions(t_run, CFRangeMake(0, t_glyph_count), t_positions);
+			CTRunGetStringIndices(t_run, CFRangeMake(0, t_glyph_count), t_indices);
 			
+			// Work out the string range of the run - the value returned by
+			// CTRunGetCharRange() can't be trusted as it considers a line
+			// 'as a whole' rather than individual runs. (This can happen with
+			// abugida scripts where you get several runs for one cluster due
+			// to font fallback).
+			CFIndex t_min_char_range = p_char_count;
+			CFIndex t_max_char_range = 0;
+			for(CFIndex i = 0; i < t_glyph_count; i++)
+			{
+				t_min_char_range = MCMin(t_min_char_range, t_indices[i]);
+				t_max_char_range = MCMax(t_max_char_range, t_indices[i] + 1);
+			}
+			CFRange t_char_range = CFRangeMake(t_min_char_range,
+											   t_max_char_range - t_min_char_range);
+
 			MCTextLayoutGlyph *t_layout_glyphs;
 			uint16_t *t_clusters;
 			t_layout_glyphs = new MCTextLayoutGlyph[t_glyph_count];
@@ -185,25 +197,26 @@ bool MCTextLayout(const unichar_t *p_chars, uint32_t p_char_count, MCFontStruct
 			}
 			
 			// Compute the clusters.
-			for(uint32_t i = 0; i < t_char_range . length; i++)
+			for(CFIndex i = 0; i < t_char_range . length; i++)
 				t_clusters[i] = 65535;
-			for(uint32_t i = 0; i < t_glyph_count; i++)
-				t_clusters[t_indices[i] - t_char_range . location] = MCMin((uint32_t)t_clusters[t_indices[i]], i);
+			for(CFIndex i = 0; i < t_glyph_count; i++)
+				t_clusters[t_indices[i] - t_char_range . location] = (uint16_t)MCMin(i, UINT16_MAX);
 			
 			for(uint32_t i = 1; i < t_char_range . length; i++)
 			{
 				// If a cluster has 0xffff as its value it means it was never set and must be
-				// part of a surrogate, so we set it to the previous char.
+				// part of a surrogate (or an out of order cluster), so we just set it to the
+				// previous char.
 				if (t_clusters[i] == 0xffff)
 					t_clusters[i] = t_clusters[i - 1];
 			}
 			
 			MCTextLayoutSpan t_span;
 			t_span . chars = p_chars + t_char_range . location;
 			t_span . clusters = t_clusters;
-			t_span . char_count = t_char_range . length;
+			t_span . char_count = (uint32_t)t_char_range . length;
 			t_span . glyphs = t_layout_glyphs;
-			t_span . glyph_count = t_glyph_count;
+			t_span . glyph_count = (uint32_t)t_glyph_count;
 			t_span . font = (void *)ctfont_from_ctfont((CTFontRef)CFDictionaryGetValue(CTRunGetAttributes(t_run), kCTFontAttributeName));
 			p_callback(p_context, &t_span);
             

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1 @@`
	`1`	`+# Ensure complex unicode scripts render correctly to PDF.`