Fix the handling of glyph positioning (gpos) offsets in vertical-upright mode.

1 files changed, 11 insertions, 3 deletions

diff --git a/gfx/thebes/gfxHarfBuzzShaper.cpp b/gfx/thebes/gfxHarfBuzzShaper.cpp
index b0cfc79be..6f7adb729 100644
--- a/gfx/thebes/gfxHarfBuzzShaper.cpp
+++ b/gfx/thebes/gfxHarfBuzzShaper.cpp
@@ -1620,7 +1620,15 @@ gfxHarfBuzzShaper::SetGlyphsFromRun(gfxContext     *aContext,
             // collect all glyphs in a list to be assigned to the first char;
             // there must be at least one in the clump, and we already measured
             // its advance, hence the placement of the loop-exit test and the
-            // measurement of the next glyph
+            // measurement of the next glyph.
+            // For vertical orientation, we add a "base offset" to compensate
+            // for the positioning within the cluster being based on horizontal
+            // glyph origin/offset.
+            hb_position_t baseIOffset, baseBOffset;
+            if (aVertical) {
+                baseIOffset = 2 * (i_offset - i_advance);
+                baseBOffset = GetGlyphHAdvance(ginfo[glyphStart].codepoint);
+            }
             while (1) {
                 gfxTextRun::DetailedGlyph* details =
                     detailedGlyphs.AppendElement();
@@ -1643,9 +1651,9 @@ gfxHarfBuzzShaper::SetGlyphsFromRun(gfxContext     *aContext,
                 }
 
                 if (aVertical) {
-                    i_offset = posInfo[glyphStart].y_offset;
+                    i_offset = baseIOffset - posInfo[glyphStart].y_offset;
                     i_advance = posInfo[glyphStart].y_advance;
-                    b_offset = posInfo[glyphStart].x_offset;
+                    b_offset = baseBOffset - posInfo[glyphStart].x_offset;
                     b_advance = posInfo[glyphStart].x_advance;
                 } else {
                     i_offset = posInfo[glyphStart].x_offset;