Made shadows blurry (thru implementing variance mapping)

include/private/SkShadowParams.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 SkShadowParams_DEFINED
+#define SkShadowParams_DEFINED
+
+/** \struct SkShadowParams
+
+    This struct holds information needed for drawing shadows.
+
+    fShadowRadius - radius of the shadow blur
+
+    fBiasingConstant - A constant used in variance shadow mapping to directly
+    0.0 - 1.0          reduce light bleeding. Essentially sets all shadows
+    ~.25               below a certain brightness equal to no light, and does
+                       a linear step on the rest. Essentially makes shadows
+                       darker and more rounded at higher values.
+
+    fMinVariance - Too low of a variance (near the outer edges of blurry
+    ~512, 1024     shadows) will lead to ugly sharp shadow brightness
+                   distortions. This enforces a minimum amount of variance
+                   in the calculation to smooth out the outside edges of
+                   blurry shadows. However, too high of a value for this will
+                   cause all shadows to be lighter by visibly different
+                   amounts varying on depth.
+
+    fType - Decides which algorithm to use to draw shadows.
+*/
+struct SkShadowParams {
+    SkScalar fShadowRadius;
+    SkScalar fBiasingConstant;
+    SkScalar fMinVariance;
+
+    enum ShadowType {
+        kNoBlur_ShadowType,
+        kVariance_ShadowType,
+
+        kLast_ShadowType = kVariance_ShadowType
+    };
+    static const int kShadowTypeCount = kLast_ShadowType + 1;
+
+    ShadowType fType;
+};
+
+#endif