Added API for Bevel NormalSource.

src/core/SkNormalSource.h

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkNormalSource_DEFINED
 #define SkNormalSource_DEFINED
 
 #include "SkFlattenable.h"
+#include "SkShader.h"
+
+class SkMatrix;
+class SkPoint3;
+
+#if SK_SUPPORT_GPU
+class GrFragmentProcessor;
+class GrContext;
+enum SkFilterQuality;
+enum SkSourceGammaTreatment;
+#endif
 
 /** Abstract class that generates or reads in normals for use by SkLightingShader.
 */
 class SK_API SkNormalSource : public SkFlattenable {
 public:
     virtual ~SkNormalSource() override;
 
 #if SK_SUPPORT_GPU
     /** Returns a fragment processor that takes no input and outputs a normal (already rotated)
         as its output color. To be used as a child fragment processor.
@@ skipping 40 matching lines @@
             N.normalize();
         The +Z axis is thus encoded in RGB as (127, 127, 255) while the -Z axis is
         (127, 127, 0).
     */
     static sk_sp<SkNormalSource> MakeFromNormalMap(sk_sp<SkShader> map, const SkMatrix& ctm);
 
     /** Returns a normal source that provides straight-up normals only (0, 0, 1).
     */
     static sk_sp<SkNormalSource> MakeFlat();
 
+    /** This enum specifies the shape of the bevel. All bevels output <0, 0, 1> as the surface
+     *  normal for any point more than 'width' away from any edge.
+     *
+     *  Mathematical details:
+     *  For the purpose of describing the shape of the bevel, we define 'w' to be the given width of
+     *  the bevel, and 'h' to be the given height. We will assume the shape is rotated such that the
+     *  point being shaded as well as the closest point in the shape's edge to that point are in the
+     *  x-axis, and the shape is translated so that the aformentioned point in the edge is at
+     *  coordinates (w, 0, 0) and the end of the bevel is at (0, 0, h).
+     *
+     */
+    enum class BevelType {
+        /* This bevel simulates a surface that is slanted from the shape's edges inwards, linearly.
+         *
+         * Mathematical details:
+         * This bevel follows a straight line from (w, 0, 0) to (0, 0, h).
+         */
+        kLinear,
+        /* This bevel simulates a surface that rounds off at the shape's edges, smoothly becoming
+         * perpendicular to the x-y plane.
+         *
+         * Mathematical details:
+         * This bevel follows the only quadratic bezier curve whose start point is at (w, 0, 0) and
+         * has a perpendicular normal vector of <1,0,0>, and whose end point is at (0, 0, h) and has
+         * a perpendicular normal vector of <0,0,1>.

[egdaniel, 2016/07/26 19:54:41]

What changes if h is negative, is confusing cause the normals you give are wrong
in that case? Maybe instead of mentioning the normals, say the control point of
the quadradic bezier is always at (w, 0, h).

[dvonbeck, 2016/07/27 17:44:57]

Done.

+         */
+        kRoundedOut,
+        /* This bevel simulates a surface that sharply becomes perpendicular to the x-y plane when
+         * at 'width' units from the nearest edge, and then rounds off towards the shape's
+         * edge, smoothly becoming paralel to the x-y plane.
+         *
+         * Mathematical details:
+         * This bevel follows the only quadratic bezier curve whose start point is at (w, 0, 0) and
+         * has a perpendicular normal vector of <0,0,1>, and whose end point is at (0, 0, h) and has
+         * a perpendicular normal vector of <1,0,0>.

[egdaniel, 2016/07/26 19:54:41]

Same as above, but control point will be at (0,0,0).

[dvonbeck, 2016/07/27 17:44:57]

Done.

+         */
+        kRoundedIn
+    };
+    /** Returns a normal source that generates a bevel for the given shape. UNIMPLEMENTED: Will
+        return straight-up normals only.
+
+        @param  type   the type of bevel to add
+        @param  width  the width of the bevel, in source space. Must be positive.
+        @param  height the height of the plateau, in source space. Can be positive, negative,
+                       or zero. A negative height means the simulated bevels slope downwards.
+    */
+    static sk_sp<SkNormalSource> MakeBevel(BevelType, SkScalar width, SkScalar height);
+
     SK_DEFINE_FLATTENABLE_TYPE(SkNormalSource)
     SK_DECLARE_FLATTENABLE_REGISTRAR_GROUP()
 };
 
 #endif