From 731b13e4e9190a45e51f855f19e88869a7718d43 Mon Sep 17 00:00:00 2001
From: Martin Hosken <martin_hosken@sil.org>
Date: Mon, 4 Mar 2019 11:12:21 +0700
Subject: [PATCH] Fix offset drift in graphite integration

---
 src/hb-graphite2.cc | 35 +++++++++++++++++++----------------
 1 file changed, 19 insertions(+), 16 deletions(-)

diff --git a/src/hb-graphite2.cc b/src/hb-graphite2.cc
index a1c602c29..fdb545342 100644
--- a/src/hb-graphite2.cc
+++ b/src/hb-graphite2.cc
@@ -225,7 +225,7 @@ struct hb_graphite2_cluster_t {
   unsigned int base_glyph;
   unsigned int num_glyphs;
   unsigned int cluster;
-  float advance;
+  unsigned int advance;
 };
 
 hb_bool_t
@@ -253,7 +253,7 @@ _hb_graphite2_shape (hb_shape_plan_t    *shape_plan HB_UNUSED,
   gr_segment *seg = nullptr;
   const gr_slot *is;
   unsigned int ci = 0, ic = 0;
-  float curradvx = 0., curradvy = 0.;
+  unsigned int curradvx = 0, curradvy = 0;
 
   unsigned int scratch_size;
   hb_buffer_t::scratch_buffer_t *scratch = buffer->get_scratch_buffer (&scratch_size);
@@ -324,11 +324,15 @@ _hb_graphite2_shape (hb_shape_plan_t    *shape_plan HB_UNUSED,
 
   hb_codepoint_t *pg = gids;
   clusters[0].cluster = buffer->info[0].cluster;
-  float curradv = 0.;
+  unsigned int upem = hb_face_get_upem (face);
+  float xscale = (float) font->x_scale / upem;
+  float yscale = (float) font->y_scale / upem;
+  yscale *= yscale / xscale;
+  unsigned int curradv = 0;
   if (HB_DIRECTION_IS_BACKWARD(buffer->props.direction))
   {
-    curradv = gr_slot_origin_X(gr_seg_first_slot(seg));
-    clusters[0].advance = gr_seg_advance_X(seg) - curradv;
+    curradv = gr_slot_origin_X(gr_seg_first_slot(seg)) * xscale;
+    clusters[0].advance = gr_seg_advance_X(seg) * xscale - curradv;
   }
   else
     clusters[0].advance = 0;
@@ -355,14 +359,17 @@ _hb_graphite2_shape (hb_shape_plan_t    *shape_plan HB_UNUSED,
       c->base_glyph = ic;
       c->num_glyphs = 0;
       if (HB_DIRECTION_IS_BACKWARD(buffer->props.direction))
-        c->advance = curradv - gr_slot_origin_X(is);
+      {
+        c->advance = curradv - gr_slot_origin_X(is) * xscale;
+        curradv -= c->advance;
+      }
       else
       {
         c->advance = 0;
-        clusters[ci].advance += gr_slot_origin_X(is) - curradv;
+        clusters[ci].advance += gr_slot_origin_X(is) * xscale - curradv;
+        curradv += clusters[ci].advance;
       }
       ci++;
-      curradv = gr_slot_origin_X(is);
     }
     clusters[ci].num_glyphs++;
 
@@ -373,7 +380,7 @@ _hb_graphite2_shape (hb_shape_plan_t    *shape_plan HB_UNUSED,
   if (HB_DIRECTION_IS_BACKWARD(buffer->props.direction))
     clusters[ci].advance += curradv;
   else
-    clusters[ci].advance += gr_seg_advance_X(seg) - curradv;
+    clusters[ci].advance += gr_seg_advance_X(seg) * xscale - curradv;
   ci++;
 
   for (unsigned int i = 0; i < ci; ++i)
@@ -388,10 +395,6 @@ _hb_graphite2_shape (hb_shape_plan_t    *shape_plan HB_UNUSED,
   }
   buffer->len = glyph_count;
 
-  unsigned int upem = hb_face_get_upem (face);
-  float xscale = (float) font->x_scale / upem;
-  float yscale = (float) font->y_scale / upem;
-  yscale *= yscale / xscale;
   /* Positioning. */
   unsigned int currclus = (unsigned int) -1;
   const hb_glyph_info_t *info = buffer->info;
@@ -404,7 +407,7 @@ _hb_graphite2_shape (hb_shape_plan_t    *shape_plan HB_UNUSED,
       pPos->x_offset = gr_slot_origin_X (is) * xscale - curradvx;
       pPos->y_offset = gr_slot_origin_Y (is) * yscale - curradvy;
       if (info->cluster != currclus) {
-	pPos->x_advance = info->var1.i32 * xscale;
+	pPos->x_advance = info->var1.i32;
 	curradvx += pPos->x_advance;
 	currclus = info->cluster;
       } else
@@ -421,7 +424,7 @@ _hb_graphite2_shape (hb_shape_plan_t    *shape_plan HB_UNUSED,
     {
       if (info->cluster != currclus)
       {
-	pPos->x_advance = info->var1.i32 * xscale;
+	pPos->x_advance = info->var1.i32;
 	curradvx -= pPos->x_advance;
 	currclus = info->cluster;
       } else
@@ -429,7 +432,7 @@ _hb_graphite2_shape (hb_shape_plan_t    *shape_plan HB_UNUSED,
 
       pPos->y_advance = gr_slot_advance_Y (is, grface, nullptr) * yscale;
       curradvy -= pPos->y_advance;
-      pPos->x_offset = (gr_slot_origin_X (is) - info->var1.i32) * xscale - curradvx + pPos->x_advance;
+      pPos->x_offset = gr_slot_origin_X (is) * xscale - info->var1.i32 - curradvx + pPos->x_advance;
       pPos->y_offset = gr_slot_origin_Y (is) * yscale - curradvy;
     }
     hb_buffer_reverse_clusters (buffer);