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+
+/*
+ * Copyright (C) 2013 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef ANDROID_HWUI_SHADOW_TESSELLATOR_H
+#define ANDROID_HWUI_SHADOW_TESSELLATOR_H
+
+#include "Debug.h"
+#include "Matrix.h"
+#include "OpenGLRenderer.h"
+#include "VertexBuffer.h"
+
+namespace android {
+namespace uirenderer {
+
+// All SHADOW_* are used to define all the geometry property of shadows.
+// Use a simplified example to illustrate the geometry setup here.
+// Assuming we use 6 rays and only 1 layer, Then we will have 2 hexagons, which
+// are 0 to 5 and 6 to 11. The area between them will be the penumbra area, and
+// the area inside the 2nd hexagon is the umbra.
+// Ambient shadow is using only 1 layer for opaque caster, otherwise, spot
+// shadow and ambient shadow are using 2 layers.
+// Triange strip indices for penumbra area: (0, 6, 1, 7, 2, 8, 3, 9, 4, 10, 5, 11, 0, 6)
+//                 0
+//
+//      5          6         1
+//           11         7
+//
+//           10         8
+//      4          9         2
+//
+//                 3
+
+// The total number of rays starting from the centroid of shadow area, in order
+// to generate the shadow geometry.
+#define SHADOW_RAY_COUNT 128
+
+// The total number of all the vertices representing the shadow.
+// For the case we only have 1 layer, then we will just fill only 2/3 of it.
+#define SHADOW_VERTEX_COUNT (3 * SHADOW_RAY_COUNT)
+
+// The total number of indices used for drawing the shadow geometry as triangle strips.
+// Depending on the mode we are drawing, we can have 1 layer or 2 layers.
+// Therefore, we only build the longer index buffer.
+#define TWO_POLY_RING_SHADOW_INDEX_COUNT (4 * (SHADOW_RAY_COUNT + 1))
+#define ONE_POLY_RING_SHADOW_INDEX_COUNT (2 * (SHADOW_RAY_COUNT + 1))
+
+#define MAX_SHADOW_INDEX_COUNT TWO_POLY_RING_SHADOW_INDEX_COUNT
+
+#define SHADOW_MIN_CASTER_Z 0.001f
+
+#define MINIMAL_DELTA_THETA (M_PI / 180 / 1000)
+
+class ShadowTessellator {
+public:
+    static void tessellateAmbientShadow(bool isCasterOpaque,
+            const Vector3* casterPolygon, int casterVertexCount,
+            const Vector3& centroid3d,  const Rect& casterBounds,
+            const Rect& localClip, float maxZ, VertexBuffer& shadowVertexBuffer);
+
+    static void tessellateSpotShadow(bool isCasterOpaque,
+            const Vector3* casterPolygon, int casterVertexCount,
+            const mat4& receiverTransform, const Vector3& lightCenter, int lightRadius,
+            const Rect& casterBounds, const Rect& localClip, VertexBuffer& shadowVertexBuffer);
+
+    static void generateShadowIndices(uint16_t*  shadowIndices);
+
+    static Vector2 centroid2d(const Vector2* poly, int polyLength);
+
+    static bool isClockwise(const Vector2* polygon, int len);
+
+    /**
+     * Determine whether the path is clockwise, using the control points.
+     *
+     * TODO: Given the skia is using inverted Y coordinate, shadow system needs
+     * to convert to the same coordinate to avoid the extra reverse.
+     *
+     * @param path The path to be examined.
+     */
+    static bool isClockwisePath(const SkPath &path);
+
+    /**
+     * Reverse the vertex array.
+     *
+     * @param polygon The vertex array to be reversed.
+     * @param len The length of the vertex array.
+     */
+    static void reverseVertexArray(Vertex* polygon, int len);
+
+}; // ShadowTessellator
+
+}; // namespace uirenderer
+}; // namespace android
+
+#endif // ANDROID_HWUI_SHADOW_TESSELLATOR_H