From f53ef69d5941514b06f5afbcd83709cf724eb74d Mon Sep 17 00:00:00 2001
From: Behdad Esfahbod <behdad@behdad.org>
Date: Fri, 4 Nov 2022 16:00:34 -0600
Subject: [PATCH] [indic] Order left-matras inside-out

Fixes https://github.com/harfbuzz/harfbuzz/issues/3863
---
 src/hb-ot-shaper-indic.cc                     |  28 +++++++++++++++++-
 src/hb-ot-shaper-myanmar.cc                   |  27 +++++++++++++++++
 ...8c53cb64b8747abdd2b70755cce2ee0eb42ef7.ttf | Bin 0 -> 3000 bytes
 ...32bb734d4c6c898a44506547d19768f0eba6a6.ttf | Bin 0 -> 2512 bytes
 .../in-house/tests/indic-special-cases.tests  |   2 ++
 .../data/in-house/tests/myanmar-misc.tests    |   1 +
 6 files changed, 57 insertions(+), 1 deletion(-)
 create mode 100644 test/shape/data/in-house/fonts/9d8c53cb64b8747abdd2b70755cce2ee0eb42ef7.ttf
 create mode 100644 test/shape/data/in-house/fonts/a232bb734d4c6c898a44506547d19768f0eba6a6.ttf

diff --git a/src/hb-ot-shaper-indic.cc b/src/hb-ot-shaper-indic.cc
index 55509c110..1f6ae5237 100644
--- a/src/hb-ot-shaper-indic.cc
+++ b/src/hb-ot-shaper-indic.cc
@@ -742,14 +742,40 @@ initial_reordering_consonant_syllable (const hb_ot_shape_plan_t *plan,
 
     /* Sit tight, rock 'n roll! */
     hb_stable_sort (info + start, end - start, compare_indic_order);
-    /* Find base again */
+
+    /* Find base again; also flip left-matra sequence. */
+    unsigned first_left_matra = end;
+    unsigned last_left_matra = end;
     base = end;
     for (unsigned int i = start; i < end; i++)
+    {
       if (info[i].indic_position() == POS_BASE_C)
       {
 	base = i;
 	break;
       }
+      else if (info[i].indic_position() == POS_PRE_M)
+      {
+        if (first_left_matra == end)
+	  first_left_matra = i;
+	last_left_matra = i;
+      }
+    }
+    /* https://github.com/harfbuzz/harfbuzz/issues/3863 */
+    if (first_left_matra < last_left_matra)
+    {
+      /* No need to merge clusters, handled later. */
+      buffer->reverse_range (first_left_matra, last_left_matra + 1);
+      /* Reverse back nuktas, etc. */
+      unsigned i = first_left_matra;
+      for (unsigned j = i; j <= last_left_matra; j++)
+        if (info[j].indic_category() == I_Cat(M))
+	{
+	  buffer->reverse_range (i, j + 1);
+	  i = j + 1;
+	}
+    }
+
     /* Things are out-of-control for post base positions, they may shuffle
      * around like crazy.  In old-spec mode, we move halants around, so in
      * that case merge all clusters after base.  Otherwise, check the sort
diff --git a/src/hb-ot-shaper-myanmar.cc b/src/hb-ot-shaper-myanmar.cc
index 78bd8de52..1039bdfeb 100644
--- a/src/hb-ot-shaper-myanmar.cc
+++ b/src/hb-ot-shaper-myanmar.cc
@@ -270,6 +270,33 @@ initial_reordering_consonant_syllable (hb_buffer_t *buffer,
 
   /* Sit tight, rock 'n roll! */
   buffer->sort (start, end, compare_myanmar_order);
+
+  /* Flip left-matra sequence. */
+  unsigned first_left_matra = end;
+  unsigned last_left_matra = end;
+  for (unsigned int i = start; i < end; i++)
+  {
+    if (info[i].myanmar_position() == POS_PRE_M)
+    {
+      if (first_left_matra == end)
+	first_left_matra = i;
+      last_left_matra = i;
+    }
+  }
+  /* https://github.com/harfbuzz/harfbuzz/issues/3863 */
+  if (first_left_matra < last_left_matra)
+  {
+    /* No need to merge clusters, done already? */
+    buffer->reverse_range (first_left_matra, last_left_matra + 1);
+    /* Reverse back VS, etc. */
+    unsigned i = first_left_matra;
+    for (unsigned j = i; j <= last_left_matra; j++)
+      if (info[j].myanmar_category() == M_Cat(VPre))
+      {
+	buffer->reverse_range (i, j + 1);
+	i = j + 1;
+      }
+  }
 }
 
 static void
diff --git a/test/shape/data/in-house/fonts/9d8c53cb64b8747abdd2b70755cce2ee0eb42ef7.ttf b/test/shape/data/in-house/fonts/9d8c53cb64b8747abdd2b70755cce2ee0eb42ef7.ttf
new file mode 100644
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GIT binary patch
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GIT binary patch
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diff --git a/test/shape/data/in-house/tests/indic-special-cases.tests b/test/shape/data/in-house/tests/indic-special-cases.tests
index 016f8947f..99ba13b30 100644
--- a/test/shape/data/in-house/tests/indic-special-cases.tests
+++ b/test/shape/data/in-house/tests/indic-special-cases.tests
@@ -2,3 +2,5 @@
 ../fonts/3cae6bfe5b57c07ba81ddbd54c02fe4f3a1e3bf6.ttf;;U+0CB0,U+200D,U+0CCD,U+0C95;[gid2=0+1334|gid6=0+358]
 ../fonts/3cae6bfe5b57c07ba81ddbd54c02fe4f3a1e3bf6.ttf;;U+0CB0,U+0CCD,U+200D,U+0C95;[gid2=0+1334|gid6=0+358]
 ../fonts/e716f6bd00a108d186b7e9f47b4515565f784f36.ttf;;U+0C1A,U+0C3F,U+0C32,U+0C4D,U+0C15,U+0C42,U+0C30,U+0C4D;[civoweltelu=0+766|latelu=2+709|uuvowelsigntelu=2+661|kasubscripttelu=2+483|rahalanttelu=6+593]
+../fonts/9d8c53cb64b8747abdd2b70755cce2ee0eb42ef7.ttf;;U+0915,U+093F,U+094E,U+093C;[uni094E=0+273|uni093C=0+0|ivowelsign03deva=0+259|uni0915=0+762]
+../fonts/9d8c53cb64b8747abdd2b70755cce2ee0eb42ef7.ttf;;U+0915,U+093F,U+093C,U+094E;[uni094E=0+273|ivowelsign00deva=0+259|uni093C=0+0|uni0915=0+762]
diff --git a/test/shape/data/in-house/tests/myanmar-misc.tests b/test/shape/data/in-house/tests/myanmar-misc.tests
index 527386394..8ba0be472 100644
--- a/test/shape/data/in-house/tests/myanmar-misc.tests
+++ b/test/shape/data/in-house/tests/myanmar-misc.tests
@@ -1 +1,2 @@
 ../fonts/065b01e54f35f0d849fd43bd5b936212739a50cb.ttf;;U+101A,U+1035;[ya_e_above=0+1000]
+../fonts/a232bb734d4c6c898a44506547d19768f0eba6a6.ttf;;U+1000,U+1031,U+1084;[e_shn=0+592|_e=0+618|ka=0+1124]