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92 lines
2.4 KiB
C++
92 lines
2.4 KiB
C++
/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef MOZILLA_GFX_POLYGON_H
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#define MOZILLA_GFX_POLYGON_H
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#include "mozilla/InitializerList.h"
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#include "nsTArray.h"
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#include "Point.h"
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namespace mozilla {
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namespace gfx {
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// BasePolygon3D stores the points of a convex planar polygon.
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template<class Units>
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class BasePolygon3D {
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public:
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explicit BasePolygon3D(const std::initializer_list<Point3DTyped<Units>>& aPoints)
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: mPoints(aPoints)
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{
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CalculateNormal();
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}
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explicit BasePolygon3D(nsTArray<Point3DTyped<Units>> && aPoints)
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: mPoints(aPoints)
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{
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CalculateNormal();
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}
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const Point3DTyped<Units>& GetNormal() const
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{
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return mNormal;
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}
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const nsTArray<Point3D>& GetPoints() const
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{
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return mPoints;
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}
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const Point3DTyped<Units>& operator[](size_t aIndex) const
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{
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MOZ_ASSERT(mPoints.Length() > aIndex);
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return mPoints[aIndex];
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}
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private:
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// Calculates the polygon surface normal.
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// The resulting normal vector will point towards the viewer when the polygon
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// has a counter-clockwise winding order from the perspective of the viewer.
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void CalculateNormal()
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{
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MOZ_ASSERT(mPoints.Length() >= 3);
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// This normal calculation method works only for planar polygons.
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mNormal = (mPoints[1] - mPoints[0]).CrossProduct(mPoints[2] - mPoints[0]);
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const float epsilon = 0.001f;
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if (mNormal.Length() < epsilon) {
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// The first three points were too close.
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// Use more points for better accuracy.
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for (size_t i = 2; i < mPoints.Length() - 1; ++i) {
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mNormal += (mPoints[i] - mPoints[0]).CrossProduct(mPoints[i + 1] - mPoints[0]);
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}
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}
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mNormal.Normalize();
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#ifdef DEBUG
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// Ensure that the polygon is planar.
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// http://mathworld.wolfram.com/Point-PlaneDistance.html
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for (const gfx::Point3DTyped<Units>& point : mPoints) {
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float d = mNormal.DotProduct(point - mPoints[0]);
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MOZ_ASSERT(std::abs(d) < epsilon);
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}
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#endif
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}
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nsTArray<Point3DTyped<Units>> mPoints;
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Point3DTyped<Units> mNormal;
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};
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typedef BasePolygon3D<UnknownUnits> Polygon3D;
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} // namespace gfx
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} // namespace mozilla
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#endif /* MOZILLA_GFX_POLYGON_H */
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