[freetype2] master d3d3ff7: [sfnt] Clarify `COLR` v1 FT_Paint* format representations

[Werner Lemberg]

branch: master
commit d3d3ff76d11acf8956108d4f66ea1068c14c3f4a
Author: Dominik Röttsches <drott@chromium.org>
Commit: Werner Lemberg <wl@gnu.org>

    [sfnt] Clarify `COLR` v1 FT_Paint* format representations
    
    * include/freetype/ftcolor.h (FT_PaintLinearGradient,
    FT_PaintRadialGradient, FT_PaintSweepGradient, FT_PaintTransform,
    FT_PaintTranslate, FT_PaintScale, FT_PaintRotate, FT_PaintSkew): Clarify
    16.16 fixed point representation of struct fields.
    * src/sfnt/ttcolr.c (read_paint): Shift coordinates for
    FT_PaintLinearGradient, FT_PaintRadialGradient, FT_PaintSweepGradient
    accordingly.
    
    Fixes: https://gitlab.freedesktop.org/freetype/freetype/-/issues/1110
---
 include/freetype/ftcolor.h | 80 +++++++++++++++++++++++++++-------------------
 src/sfnt/ttcolr.c          | 36 +++++++++++++--------
 2 files changed, 70 insertions(+), 46 deletions(-)

diff --git a/include/freetype/ftcolor.h b/include/freetype/ftcolor.h
index cbd2d85..08dbac0 100644
--- a/include/freetype/ftcolor.h
+++ b/include/freetype/ftcolor.h
@@ -870,13 +870,16 @@ FT_BEGIN_HEADER
    *     color stops along the gradient.
    *
    *   p0 ::
-   *     The starting point of the gradient definition (in font units).
+   *     The starting point of the gradient definition in font units
+   *     represented as a 16.16 fixed-point `FT_Vector`.
    *
    *   p1 ::
-   *     The end point of the gradient definition (in font units).
+   *     The end point of the gradient definition in font units
+   *     represented as a 16.16 fixed-point `FT_Vector`.
    *
    *   p2 ::
-   *     Optional point~p2 to rotate the gradient (in font units).
+   *     Optional point~p2 to rotate the gradient in font units
+   *     represented as a 16.16 fixed-point `FT_Vector`.
    *     Otherwise equal to~p0.
    *
    * @since:
@@ -914,19 +917,20 @@ FT_BEGIN_HEADER
    *     color stops along the gradient.
    *
    *   c0 ::
-   *     The center of the starting point of the radial gradient (in font
-   *     units).
+   *     The center of the starting point of the radial gradient in font
+   *     units represented as a 16.16 fixed-point `FT_Vector`.
    *
    *   r0 ::
-   *     The radius of the starting circle of the radial gradient (in font
-   *     units).
+   *     The radius of the starting circle of the radial gradient in font
+   *     units represented as a 16.16 fixed-point value.
    *
    *   c1 ::
-   *     The center of the end point of the radial gradient (in font units).
+   *     The center of the end point of the radial gradient in font units
+   *     represented as a 16.16 fixed-point `FT_Vector`.
    *
    *   r1 ::
-   *     The radius of the end circle of the radial gradient (in font
-   *     units).
+   *     The radius of the end circle of the radial gradient in font
+   *     units represented as a 16.16 fixed-point value.
    *
    * @since:
    *   2.11 -- **currently experimental only!**  There might be changes
@@ -938,9 +942,9 @@ FT_BEGIN_HEADER
     FT_ColorLine  colorline;
 
     FT_Vector  c0;
-    FT_UShort  r0;
+    FT_Pos     r0;
     FT_Vector  c1;
-    FT_UShort  r1;
+    FT_Pos     r1;
 
   } FT_PaintRadialGradient;
 
@@ -963,16 +967,17 @@ FT_BEGIN_HEADER
    *     color stops along the gradient.
    *
    *   center ::
-   *     The center of the sweep gradient (in font units).
+   *     The center of the sweep gradient in font units represented as a
+   *     vector of 16.16 fixed-point values.
    *
    *   start_angle ::
-   *     The start angle of the sweep gradient, in 16.16 fixed point
+   *     The start angle of the sweep gradient in 16.16 fixed-point
    *     format specifying degrees divided by 180.0 (as in the
    *     spec).  Multiply by 180.0f to receive degrees value.  Values are
    *     given counter-clockwise, starting from the (positive) y~axis.
    *
    *   end_angle ::
-   *     The end angle of the sweep gradient, in 16.16 fixed point
+   *     The end angle of the sweep gradient in 16.16 fixed-point
    *     format specifying degrees divided by 180.0 (as in the
    *     spec).  Multiply by 180.0f to receive degrees value.  Values are
    *     given counter-clockwise, starting from the (positive) y~axis.
@@ -1061,7 +1066,8 @@ FT_BEGIN_HEADER
    *     An opaque paint that is subject to being transformed.
    *
    *   affine ::
-   *     A 2x3 transformation matrix in @FT_Affine23 format.
+   *     A 2x3 transformation matrix in @FT_Affine23 format containing
+   *     16.16 fixed-point values.
    *
    * @since:
    *   2.11 -- **currently experimental only!**  There might be changes
@@ -1091,10 +1097,12 @@ FT_BEGIN_HEADER
    *     rotated.
    *
    *   dx ::
-   *     Translation in x~direction (in font units).
+   *     Translation in x~direction in font units represented as a
+   *     16.16 fixed-point value.
    *
    *   dy ::
-   *     Translation in y~direction (in font units).
+   *     Translation in y~direction in font units represented as a
+   *     16.16 fixed-point value.
    *
    * @since:
    *   2.11 -- **currently experimental only!**  There might be changes
@@ -1132,16 +1140,20 @@ FT_BEGIN_HEADER
    *     scaled.
    *
    *   scale_x ::
-   *     Scale factor in x~direction.
+   *     Scale factor in x~direction represented as a
+   *     16.16 fixed-point value.
    *
    *   scale_y ::
-   *     Scale factor in y~direction.
+   *     Scale factor in y~direction represented as a
+   *     16.16 fixed-point value.
    *
    *   center_x ::
-   *     x~coordinate of center point to scale from.
+   *     x~coordinate of center point to scale from represented as a
+   *     16.16 fixed-point value.
    *
    *   center_y ::
-   *     y~coordinate of center point to scale from.
+   *     y~coordinate of center point to scale from represented as a
+   *     16.16 fixed-point value.
    *
    * @since:
    *   2.11 -- **currently experimental only!**  There might be changes
@@ -1177,16 +1189,16 @@ FT_BEGIN_HEADER
    *
    *   angle ::
    *     The rotation angle that is to be applied in degrees divided by
-   *     180.0 (as in the spec).  Multiply by 180.0f to receive degrees
-   *     value.
+   *     180.0 (as in the spec) represented as a 16.16 fixed-point
+   *     value.  Multiply by 180.0f to receive degrees value.
    *
    *   center_x ::
-   *     The x~coordinate of the pivot point of the rotation (in font
-   *     units).
+   *     The x~coordinate of the pivot point of the rotation in font
+   *     units) represented as a 16.16 fixed-point value.
    *
    *   center_y ::
-   *     The y~coordinate of the pivot point of the rotation (in font
-   *     units).
+   *     The y~coordinate of the pivot point of the rotation in font
+   *     units represented as a 16.16 fixed-point value.
    *
    * @since:
    *   2.11 -- **currently experimental only!**  There might be changes
@@ -1223,17 +1235,21 @@ FT_BEGIN_HEADER
    *
    *   x_skew_angle ::
    *     The skewing angle in x~direction in degrees divided by 180.0
-   *     (as in the spec).  Multiply by 180.0f to receive degrees.
+   *     (as in the spec) represented as a 16.16 fixed-point
+   *     value. Multiply by 180.0f to receive degrees.
    *
    *   y_skew_angle ::
    *     The skewing angle in y~direction in degrees divided by 180.0
-   *     (as in the spec).  Multiply by 180.0f to receive degrees.
+   *     (as in the spec) represented as a 16.16 fixed-point
+   *     value.  Multiply by 180.0f to receive degrees.
    *
    *   center_x ::
-   *     The x~coordinate of the pivot point of the skew (in font units).
+   *     The x~coordinate of the pivot point of the skew in font units
+   *     represented as a 16.16 fixed-point value.
    *
    *   center_y ::
-   *     The y~coordinate of the pivot point of the skew (in font units).
+   *     The y~coordinate of the pivot point of the skew in font units
+   *     represented as a 16.16 fixed-point value.
    *
    * @since:
    *   2.11 -- **currently experimental only!**  There might be changes
diff --git a/src/sfnt/ttcolr.c b/src/sfnt/ttcolr.c
index 8b31b20..deec80b 100644
--- a/src/sfnt/ttcolr.c
+++ b/src/sfnt/ttcolr.c
@@ -505,12 +505,16 @@
                              &apaint->u.linear_gradient.colorline ) )
         return 0;
 
-      apaint->u.linear_gradient.p0.x = FT_NEXT_SHORT( p );
-      apaint->u.linear_gradient.p0.y = FT_NEXT_SHORT( p );
-      apaint->u.linear_gradient.p1.x = FT_NEXT_SHORT( p );
-      apaint->u.linear_gradient.p1.y = FT_NEXT_SHORT( p );
-      apaint->u.linear_gradient.p2.x = FT_NEXT_SHORT( p );
-      apaint->u.linear_gradient.p2.y = FT_NEXT_SHORT( p );
+      /*
+       * In order to support variations expose these as FT_Fixed 16.16 values 
so
+       * that we can support fractional values after interpolation.
+       */
+      apaint->u.linear_gradient.p0.x = FT_NEXT_SHORT( p ) << 16;
+      apaint->u.linear_gradient.p0.y = FT_NEXT_SHORT( p ) << 16;
+      apaint->u.linear_gradient.p1.x = FT_NEXT_SHORT( p ) << 16;
+      apaint->u.linear_gradient.p1.y = FT_NEXT_SHORT( p ) << 16;
+      apaint->u.linear_gradient.p2.x = FT_NEXT_SHORT( p ) << 16;
+      apaint->u.linear_gradient.p2.y = FT_NEXT_SHORT( p ) << 16;
 
       return 1;
     }
@@ -521,15 +525,15 @@
                              &apaint->u.radial_gradient.colorline ) )
         return 0;
 
-      apaint->u.radial_gradient.c0.x = FT_NEXT_SHORT( p );
-      apaint->u.radial_gradient.c0.y = FT_NEXT_SHORT( p );
+      apaint->u.radial_gradient.c0.x = FT_NEXT_SHORT( p ) << 16;
+      apaint->u.radial_gradient.c0.y = FT_NEXT_SHORT( p ) << 16;
 
-      apaint->u.radial_gradient.r0 = FT_NEXT_USHORT( p );
+      apaint->u.radial_gradient.r0 = FT_NEXT_USHORT( p ) << 16;
 
-      apaint->u.radial_gradient.c1.x = FT_NEXT_SHORT( p );
-      apaint->u.radial_gradient.c1.y = FT_NEXT_SHORT( p );
+      apaint->u.radial_gradient.c1.x = FT_NEXT_SHORT( p ) << 16;
+      apaint->u.radial_gradient.c1.y = FT_NEXT_SHORT( p ) << 16;
 
-      apaint->u.radial_gradient.r1 = FT_NEXT_USHORT( p );
+      apaint->u.radial_gradient.r1 = FT_NEXT_USHORT( p ) << 16;
 
       return 1;
     }
@@ -540,8 +544,8 @@
                              &apaint->u.sweep_gradient.colorline ) )
         return 0;
 
-      apaint->u.sweep_gradient.center.x = FT_NEXT_SHORT( p );
-      apaint->u.sweep_gradient.center.y = FT_NEXT_SHORT( p );
+      apaint->u.sweep_gradient.center.x = FT_NEXT_SHORT( p ) << 16;
+      apaint->u.sweep_gradient.center.y = FT_NEXT_SHORT( p ) << 16;
 
       apaint->u.sweep_gradient.start_angle = FT_NEXT_SHORT( p ) << 2;
       apaint->u.sweep_gradient.end_angle   = FT_NEXT_SHORT( p ) << 2;
@@ -568,6 +572,10 @@
 
       p = child_table_p;
 
+      /*
+       * The following matrix coefficients are encoded as
+       * OpenType 16.16 fixed-point values.
+       */
       apaint->u.transform.affine.xx = FT_NEXT_LONG( p );
       apaint->u.transform.affine.yx = FT_NEXT_LONG( p );
       apaint->u.transform.affine.xy = FT_NEXT_LONG( p );