[sfnt] Support variable 'COLR' v1 color lines.

* include/freetype/ftcolor.h (FT_ColorStopIterator): Add field
`read_variable` to indicate whether a variation index base should be read.

* src/sfnt/ttcolr.c: (FT_PaintFormat_Internal): New enumerations
`FT_COLR_PAINTFORMAT_INTERNAL_VAR_LINEAR_GRADIENT`
`FT_COLR_PAINTFORMAT_INTERNAL_VAR_RADIAL_GRADIENT`, and
`FT_COLR_PAINTFORMAT_INTERNAL_VAR_SWEEP_GRADIENT`.
(read_color_line): New parameter `read_variable`; update callers.
(read_paint): Handle new enumerations.

2 files changed, 66 insertions, 11 deletions

diff --git a/include/freetype/ftcolor.h b/include/freetype/ftcolor.h
index 13285683f..17f1dd89c 100644
--- a/include/freetype/ftcolor.h
+++ b/include/freetype/ftcolor.h
@@ -521,9 +521,10 @@ FT_BEGIN_HEADER
    *
    * @description:
    *   This iterator object is needed for @FT_Get_Colorline_Stops.  It keeps
-   *   state while iterating over the stops of an @FT_ColorLine,
-   *   representing the `ColorLine` struct of the v1 extensions to 'COLR',
-   *   see 'https://github.com/googlefonts/colr-gradients-spec'.
+   *   state while iterating over the stops of an @FT_ColorLine, representing
+   *   the `ColorLine` struct of the v1 extensions to 'COLR', see
+   *   'https://github.com/googlefonts/colr-gradients-spec'.  Do not manually
+   *   modify fields of this iterator.
    *
    * @fields:
    *   num_color_stops ::
@@ -537,6 +538,10 @@ FT_BEGIN_HEADER
    *     An opaque pointer into 'COLR' table data.  Set by @FT_Get_Paint.
    *     Updated by @FT_Get_Colorline_Stops.
    *
+   *   read_variable ::
+   *     A boolean keeping track of whether variable color lines are to be
+   *     read.  Set by @FT_Get_Paint.
+   *
    * @since:
    *   2.11 -- **currently experimental only!**  There might be changes
    *   without retaining backward compatibility of both the API and ABI.
@@ -549,6 +554,8 @@ FT_BEGIN_HEADER
 
     FT_Byte*  p;
 
+    FT_Bool  read_variable;
+
   } FT_ColorStopIterator;
 
 
diff --git a/src/sfnt/ttcolr.c b/src/sfnt/ttcolr.c
index f10113eb2..e8a3d65ac 100644
--- a/src/sfnt/ttcolr.c
+++ b/src/sfnt/ttcolr.c
@@ -66,6 +66,9 @@
   typedef enum  FT_PaintFormat_Internal_
   {
     FT_COLR_PAINTFORMAT_INTERNAL_VAR_SOLID            = 3,
+    FT_COLR_PAINTFORMAT_INTERNAL_VAR_LINEAR_GRADIENT  = 5,
+    FT_COLR_PAINTFORMAT_INTERNAL_VAR_RADIAL_GRADIENT  = 7,
+    FT_COLR_PAINTFORMAT_INTERNAL_VAR_SWEEP_GRADIENT   = 9,
     FT_COLR_PAINTFORMAT_INTERNAL_SCALE_CENTER         = 18,
     FT_COLR_PAINTFORMAT_INTERNAL_SCALE_UNIFORM        = 20,
     FT_COLR_PAINTFORMAT_INTERNAL_SCALE_UNIFORM_CENTER = 22,
@@ -477,8 +480,9 @@
 
 
   static FT_Bool
-  read_color_line( FT_Byte*      color_line_p,
-                   FT_ColorLine  *colorline )
+  read_color_line( FT_Byte*       color_line_p,
+                   FT_ColorLine*  colorline,
+                   FT_Bool        read_variable )
   {
     FT_Byte*        p = color_line_p;
     FT_PaintExtend  paint_extend;
@@ -493,6 +497,7 @@
     colorline->color_stop_iterator.num_color_stops    = FT_NEXT_USHORT( p );
     colorline->color_stop_iterator.p                  = p;
     colorline->color_stop_iterator.current_color_stop = 0;
+    colorline->color_stop_iterator.read_variable      = read_variable;
 
     return 1;
   }
@@ -604,6 +609,7 @@
   {
     FT_Byte*         paint_base      = p;
     FT_Byte*         child_table_p   = NULL;
+    FT_Bool          do_read_var     = FALSE;
     FT_ULong         var_index_base  = 0;
     /* Longest varIndexBase offset is 5 in the spec. */
     FT_ItemVarDelta  item_deltas[6]  = { 0, 0, 0, 0, 0, 0 };
@@ -691,10 +697,14 @@
     if ( !get_child_table_pointer( colr, paint_base, &p, &child_table_p ) )
       return 0;
 
-    if ( apaint->format == FT_COLR_PAINTFORMAT_LINEAR_GRADIENT )
+    if ( apaint->format == FT_COLR_PAINTFORMAT_LINEAR_GRADIENT    ||
+         ( do_read_var =
+           ( (FT_PaintFormat_Internal)apaint->format ==
+             FT_COLR_PAINTFORMAT_INTERNAL_VAR_LINEAR_GRADIENT ) ) )
     {
       if ( !read_color_line( child_table_p,
-                             &apaint->u.linear_gradient.colorline ) )
+                             &apaint->u.linear_gradient.colorline,
+                             do_read_var ) )
         return 0;
 
       /*
@@ -708,16 +718,22 @@
       apaint->u.linear_gradient.p2.x = INT_TO_FIXED( FT_NEXT_SHORT( p ) );
       apaint->u.linear_gradient.p2.y = INT_TO_FIXED( FT_NEXT_SHORT( p ) );
 
+      apaint->format = FT_COLR_PAINTFORMAT_LINEAR_GRADIENT;
+
       return 1;
     }
 
-    else if ( apaint->format == FT_COLR_PAINTFORMAT_RADIAL_GRADIENT )
+    else if ( apaint->format == FT_COLR_PAINTFORMAT_RADIAL_GRADIENT    ||
+              ( do_read_var =
+                ( (FT_PaintFormat_Internal)apaint->format ==
+                  FT_COLR_PAINTFORMAT_INTERNAL_VAR_RADIAL_GRADIENT ) ) )
     {
       FT_Pos  tmp;
 
 
       if ( !read_color_line( child_table_p,
-                             &apaint->u.radial_gradient.colorline ) )
+                             &apaint->u.radial_gradient.colorline,
+                             do_read_var ) )
         return 0;
 
       /* In the OpenType specification, `r0` and `r1` are defined as   */
@@ -737,13 +753,19 @@
       tmp                          = INT_TO_FIXED( FT_NEXT_SHORT( p ) );
       apaint->u.radial_gradient.r1 = tmp < 0 ? FT_INT_MAX : tmp;
 
+      apaint->format = FT_COLR_PAINTFORMAT_RADIAL_GRADIENT;
+
       return 1;
     }
 
-    else if ( apaint->format == FT_COLR_PAINTFORMAT_SWEEP_GRADIENT )
+    else if ( apaint->format == FT_COLR_PAINTFORMAT_SWEEP_GRADIENT    ||
+              ( do_read_var =
+                ( (FT_PaintFormat_Internal)apaint->format ==
+                  FT_COLR_PAINTFORMAT_INTERNAL_VAR_SWEEP_GRADIENT ) ) )
     {
       if ( !read_color_line( child_table_p,
-                             &apaint->u.sweep_gradient.colorline ) )
+                             &apaint->u.sweep_gradient.colorline,
+                             do_read_var) )
         return 0;
 
       apaint->u.sweep_gradient.center.x =
@@ -756,6 +778,8 @@
       apaint->u.sweep_gradient.end_angle =
           F2DOT14_TO_FIXED( FT_NEXT_SHORT( p ) );
 
+      apaint->format = FT_COLR_PAINTFORMAT_SWEEP_GRADIENT;
+
       return 1;
     }
 
@@ -1228,6 +1252,8 @@
     Colr*  colr = (Colr*)face->colr;
 
     FT_Byte*  p;
+    FT_Long   var_index_base;
+    FT_Int    item_deltas[2];
 
 
     if ( !colr || !colr->table )
@@ -1251,6 +1277,28 @@
 
     color_stop->color.alpha = FT_NEXT_SHORT( p );
 
+    if ( iterator->read_variable )
+    {
+      /* Pointer p needs to be advanced independently of whether we intend */
+      /* to take variable deltas into account or not.  Otherwise iteration */
+      /* would fail due to wrong offsets.                                  */
+      var_index_base = FT_NEXT_ULONG( p );
+
+#ifdef TT_CONFIG_OPTION_GX_VAR_SUPPORT
+      if ( VARIABLE_COLRV1_ENABLED )
+      {
+        if ( !get_deltas_for_var_index_base( face, colr,
+                                             var_index_base,
+                                             2,
+                                             item_deltas ) )
+          return 0;
+
+        color_stop->stop_offset += (FT_Fixed)item_deltas[0] << 2;
+        color_stop->color.alpha += item_deltas[1];
+      }
+#endif
+    }
+
     iterator->p = p;
     iterator->current_color_stop++;