1 files changed, 295 insertions, 0 deletions
diff --git a/gfx/2d/Polygon.h b/gfx/2d/Polygon.h
new file mode 100644
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+++ b/gfx/2d/Polygon.h
@@ -0,0 +1,295 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef MOZILLA_GFX_POLYGON_H
+#define MOZILLA_GFX_POLYGON_H
+
+#include "Matrix.h"
+#include "mozilla/Move.h"
+#include "nsTArray.h"
+#include "Point.h"
+#include "Triangle.h"
+
+#include <initializer_list>
+
+namespace mozilla {
+namespace gfx {
+
+// Polygon3DTyped stores the points of a convex planar polygon.
+template<class Units>
+class Polygon3DTyped {
+public:
+  Polygon3DTyped() {}
+
+  explicit Polygon3DTyped(const std::initializer_list<Point3DTyped<Units>>& aPoints,
+                          Point3DTyped<Units> aNormal =
+                            Point3DTyped<Units>(0.0f, 0.0f, 1.0f))
+    : mNormal(aNormal), mPoints(aPoints)
+  {
+#ifdef DEBUG
+    EnsurePlanarPolygon();
+#endif
+  }
+
+  explicit Polygon3DTyped(nsTArray<Point3DTyped<Units>>&& aPoints,
+                          Point3DTyped<Units> aNormal =
+                            Point3DTyped<Units>(0.0f, 0.0f, 1.0f))
+    : mNormal(aNormal), mPoints(Move(aPoints))
+  {
+#ifdef DEBUG
+    EnsurePlanarPolygon();
+#endif
+  }
+
+  explicit Polygon3DTyped(const nsTArray<Point3DTyped<Units>>& aPoints,
+                          Point3DTyped<Units> aNormal =
+                            Point3DTyped<Units>(0.0f, 0.0f, 1.0f))
+    : mNormal(aNormal), mPoints(aPoints)
+  {
+#ifdef DEBUG
+    EnsurePlanarPolygon();
+#endif
+  }
+
+  RectTyped<Units> BoundingBox() const
+  {
+    float minX, maxX, minY, maxY;
+    minX = maxX = mPoints[0].x;
+    minY = maxY = mPoints[0].y;
+
+    for (const Point3DTyped<Units>& point : mPoints) {
+      minX = std::min(point.x, minX);
+      maxX = std::max(point.x, maxX);
+
+      minY = std::min(point.y, minY);
+      maxY = std::max(point.y, maxY);
+    }
+
+    return RectTyped<Units>(minX, minY, maxX - minX, maxY - minY);
+  }
+
+  nsTArray<float>
+  CalculateDotProducts(const Polygon3DTyped<Units>& aPlane,
+                       size_t& aPos, size_t& aNeg) const
+  {
+    // Point classification might produce incorrect results due to numerical
+    // inaccuracies. Using an epsilon value makes the splitting plane "thicker".
+    const float epsilon = 0.05f;
+
+    MOZ_ASSERT(!aPlane.GetPoints().IsEmpty());
+    const Point3DTyped<Units>& planeNormal = aPlane.GetNormal();
+    const Point3DTyped<Units>& planePoint = aPlane[0];
+
+    aPos = aNeg = 0;
+    nsTArray<float> dotProducts;
+    for (const Point3DTyped<Units>& point : mPoints) {
+      float dot = (point - planePoint).DotProduct(planeNormal);
+
+      if (dot > epsilon) {
+        aPos++;
+      } else if (dot < -epsilon) {
+        aNeg++;
+      } else {
+        // The point is within the thick plane.
+        dot = 0.0f;
+      }
+
+      dotProducts.AppendElement(dot);
+    }
+
+    return dotProducts;
+  }
+
+  // Clips the polygon against the given 2D rectangle.
+  Polygon3DTyped<Units> ClipPolygon(const RectTyped<Units>& aRect) const
+  {
+    Polygon3DTyped<Units> polygon(mPoints, mNormal);
+
+    // Left edge
+    ClipPolygonWithEdge(polygon, aRect.BottomLeft(), aRect.TopLeft());
+
+    // Bottom edge
+    ClipPolygonWithEdge(polygon, aRect.BottomRight(), aRect.BottomLeft());
+
+    // Right edge
+    ClipPolygonWithEdge(polygon, aRect.TopRight(), aRect.BottomRight());
+
+    // Top edge
+    ClipPolygonWithEdge(polygon, aRect.TopLeft(), aRect.TopRight());
+
+    return polygon;
+  }
+
+  const Point3DTyped<Units>& GetNormal() const
+  {
+    return mNormal;
+  }
+
+  const nsTArray<Point3DTyped<Units>>& GetPoints() const
+  {
+    return mPoints;
+  }
+
+  const Point3DTyped<Units>& operator[](size_t aIndex) const
+  {
+    MOZ_ASSERT(mPoints.Length() > aIndex);
+    return mPoints[aIndex];
+  }
+
+  void SplitPolygon(const Polygon3DTyped<Units>& aSplittingPlane,
+                    const nsTArray<float>& aDots,
+                    nsTArray<Point3DTyped<Units>>& aBackPoints,
+                    nsTArray<Point3DTyped<Units>>& aFrontPoints) const
+  {
+    static const auto Sign = [](const float& f) {
+      if (f > 0.0f) return 1;
+      if (f < 0.0f) return -1;
+      return 0;
+    };
+
+    const Point3DTyped<Units>& normal = aSplittingPlane.GetNormal();
+    const size_t pointCount = mPoints.Length();
+
+    for (size_t i = 0; i < pointCount; ++i) {
+      size_t j = (i + 1) % pointCount;
+
+      const Point3DTyped<Units>& a = mPoints[i];
+      const Point3DTyped<Units>& b = mPoints[j];
+      const float dotA = aDots[i];
+      const float dotB = aDots[j];
+
+      // The point is in front of or on the plane.
+      if (dotA >= 0) {
+        aFrontPoints.AppendElement(a);
+      }
+
+      // The point is behind or on the plane.
+      if (dotA <= 0) {
+        aBackPoints.AppendElement(a);
+      }
+
+      // If the sign of the dot products changes between two consecutive
+      // vertices, then the plane intersects with the polygon edge.
+      // The case where the polygon edge is within the plane is handled above.
+      if (Sign(dotA) && Sign(dotB) && Sign(dotA) != Sign(dotB)) {
+        // Calculate the line segment and plane intersection point.
+        const Point3DTyped<Units> ab = b - a;
+        const float dotAB = ab.DotProduct(normal);
+        const float t = -dotA / dotAB;
+        const Point3DTyped<Units> p = a + (ab * t);
+
+        // Add the intersection point to both polygons.
+        aBackPoints.AppendElement(p);
+        aFrontPoints.AppendElement(p);
+      }
+    }
+  }
+
+  nsTArray<TriangleTyped<Units>> ToTriangles() const
+  {
+    nsTArray<TriangleTyped<Units>> triangles;
+
+    if (mPoints.Length() < 3) {
+      return triangles;
+    }
+
+    for (size_t i = 1; i < mPoints.Length() - 1; ++i) {
+      TriangleTyped<Units> triangle(Point(mPoints[0].x, mPoints[0].y),
+                                    Point(mPoints[i].x, mPoints[i].y),
+                                    Point(mPoints[i+1].x, mPoints[i+1].y));
+      triangles.AppendElement(Move(triangle));
+    }
+
+    return triangles;
+  }
+
+  void TransformToLayerSpace(const Matrix4x4Typed<Units, Units>& aTransform)
+  {
+    TransformPoints(aTransform);
+    mNormal = Point3DTyped<Units>(0.0f, 0.0f, 1.0f);
+  }
+
+  void TransformToScreenSpace(const Matrix4x4Typed<Units, Units>& aTransform)
+  {
+    TransformPoints(aTransform);
+
+    // Normal vectors should be transformed using inverse transpose.
+    mNormal = aTransform.Inverse().Transpose().TransformPoint(mNormal);
+  }
+
+private:
+  void ClipPolygonWithEdge(Polygon3DTyped<Units>& aPolygon,
+                           const PointTyped<Units>& aFirst,
+                           const PointTyped<Units>& aSecond) const
+  {
+    const Point3DTyped<Units> a(aFirst.x, aFirst.y, 0.0f);
+    const Point3DTyped<Units> b(aSecond.x, aSecond.y, 0.0f);
+    const Point3DTyped<Units> normal(b.y - a.y, a.x - b.x, 0.0f);
+    Polygon3DTyped<Units> plane({a, b}, normal);
+
+    size_t pos, neg;
+    nsTArray<float> dots = aPolygon.CalculateDotProducts(plane, pos, neg);
+
+    nsTArray<Point3DTyped<Units>> backPoints, frontPoints;
+    aPolygon.SplitPolygon(plane, dots, backPoints, frontPoints);
+
+    // Only use the points that are behind the clipping plane.
+    aPolygon = Polygon3DTyped<Units>(Move(backPoints), aPolygon.GetNormal());
+  }
+
+#ifdef DEBUG
+  void EnsurePlanarPolygon() const
+  {
+    if (mPoints.Length() <= 3) {
+      // Polygons with three or less points are guaranteed to be planar.
+      return;
+    }
+
+    // This normal calculation method works only for planar polygons.
+    // The resulting normal vector will point towards the viewer when the
+    // polygon has a counter-clockwise winding order from the perspective
+    // of the viewer.
+    Point3DTyped<Units> normal;
+
+    for (size_t i = 1; i < mPoints.Length() - 1; ++i) {
+      normal +=
+        (mPoints[i] - mPoints[0]).CrossProduct(mPoints[i + 1] - mPoints[0]);
+    }
+
+    // Ensure that at least one component is greater than zero.
+    // This avoids division by zero when normalizing the vector.
+    bool hasNonZeroComponent = std::abs(normal.x) > 0.0f ||
+                               std::abs(normal.y) > 0.0f ||
+                               std::abs(normal.z) > 0.0f;
+    MOZ_ASSERT(hasNonZeroComponent);
+
+    normal.Normalize();
+
+    // Ensure that the polygon is planar.
+    // http://mathworld.wolfram.com/Point-PlaneDistance.html
+    const float epsilon = 0.01f;
+    for (const Point3DTyped<Units>& point : mPoints) {
+      float d = normal.DotProduct(point - mPoints[0]);
+      MOZ_ASSERT(std::abs(d) < epsilon);
+    }
+  }
+#endif
+  void TransformPoints(const Matrix4x4Typed<Units, Units>& aTransform)
+  {
+    for (Point3DTyped<Units>& point : mPoints) {
+      point = aTransform.TransformPoint(point);
+    }
+  }
+
+  Point3DTyped<Units> mNormal;
+  nsTArray<Point3DTyped<Units>> mPoints;
+};
+
+typedef Polygon3DTyped<UnknownUnits> Polygon3D;
+
+} // namespace gfx
+} // namespace mozilla
+
+#endif /* MOZILLA_GFX_POLYGON_H */