commit 0348c627b19864203c0eb3752f49850851a65200
author Dominik Röttsches <drott@chromium.org> Tue Jun 29 20:51:32 2021 +0300
committer Werner Lemberg <wl@gnu.org> Thu Jul 01 06:15:22 2021 +0200
tree d21ddf20bf9be4e456d39cf80927dfdb8b89dedc
parent f27b4834b7dcf9d667fd5173106be0cddb0ec1c2

[sfnt] Handle fonts without layer list in 'COLR' v1.

'COLR' v1 fonts do not necessarily need to have a layer list; for
this reason, 'fontTools' recently started generating fonts in a way
that drops the layer list if there are no layers in it.  This
results in the layer list offset becoming zero, which FreeType
treated as an invalid table.  Fix that and handle the case for layer
list offset being 0.  This slightly changes how we need to calculate
the starting offset for paints.

* src/sfnt/ttcolr.c (tt_face_load_colr): Handle case of layer list
offset being zero without outright rejecting table.

ChangeLog

diff --git a/ChangeLog b/ChangeLog
index a1de346..eccf4a1 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,18 @@
+2021-06-30  Dominik Röttsches  <drott@chromium.org>
+
+	[sfnt] Handle fonts without layer list in 'COLR' v1.
+
+	'COLR' v1 fonts do not necessarily need to have a layer list; for
+	this reason, 'fontTools' recently started generating fonts in a way
+	that drops the layer list if there are no layers in it.  This
+	results in the layer list offset becoming zero, which FreeType
+	treated as an invalid table.  Fix that and handle the case for layer
+	list offset being 0.  This slightly changes how we need to calculate
+	the starting offset for paints.
+
+	* src/sfnt/ttcolr.c (tt_face_load_colr): Handle case of layer list
+	offset being zero without outright rejecting table.
+
 2021-06-30  Alexei Podtelezhnikov  <apodtele@gmail.com>
 
 	* src/raster/ftraster.c (Render_Single_Pass): Simplify `band_stack'.

src/sfnt/ttcolr.c

diff --git a/src/sfnt/ttcolr.c b/src/sfnt/ttcolr.c
index 1e297ac..34accdd 100644
--- a/src/sfnt/ttcolr.c
+++ b/src/sfnt/ttcolr.c
@@ -186,24 +186,35 @@
 
       layer_offset_v1 = FT_NEXT_ULONG( p );
 
-      if ( !layer_offset_v1 || layer_offset_v1 >= table_size )
+      if ( layer_offset_v1 >= table_size )
         goto InvalidTable;
 
-      p1            = (FT_Byte*)( table + layer_offset_v1 );
-      num_layers_v1 = FT_PEEK_ULONG( p1 );
+      if ( layer_offset_v1 )
+      {
+        p1            = (FT_Byte*)( table + layer_offset_v1 );
+        num_layers_v1 = FT_PEEK_ULONG( p1 );
 
-      if ( num_layers_v1 * LAYER_V1_LIST_PAINT_OFFSET_SIZE >
-             table_size - layer_offset_v1 )
-        goto InvalidTable;
+        if ( num_layers_v1 * LAYER_V1_LIST_PAINT_OFFSET_SIZE >
+               table_size - layer_offset_v1 )
+          goto InvalidTable;
 
-      colr->num_layers_v1 = num_layers_v1;
-      colr->layers_v1     = p1;
+        colr->num_layers_v1 = num_layers_v1;
+        colr->layers_v1     = p1;
 
-      colr->paints_start_v1 =
-        FT_MIN( colr->base_glyphs_v1 +
-                  colr->num_base_glyphs_v1 * BASE_GLYPH_PAINT_RECORD_SIZE,
-                colr->layers_v1 +
-                  colr->num_layers_v1 * LAYER_V1_LIST_PAINT_OFFSET_SIZE );
+        colr->paints_start_v1 =
+            FT_MIN( colr->base_glyphs_v1 +
+                    colr->num_base_glyphs_v1 * BASE_GLYPH_PAINT_RECORD_SIZE,
+                    colr->layers_v1 +
+                    colr->num_layers_v1 * LAYER_V1_LIST_PAINT_OFFSET_SIZE );
+      }
+      else
+      {
+        colr->num_layers_v1   = 0;
+        colr->layers_v1       = 0;
+        colr->paints_start_v1 =
+          colr->base_glyphs_v1 +
+          colr->num_base_glyphs_v1 * BASE_GLYPH_PAINT_RECORD_SIZE;
+      }
     }
 
     colr->base_glyphs = (FT_Byte*)( table + base_glyph_offset );