130 lines
3.6 KiB
C++
130 lines
3.6 KiB
C++
/*
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Bullet Continuous Collision Detection and Physics Library
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Copyright (c) 2011 Advanced Micro Devices, Inc. http://bulletphysics.org
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This software is provided 'as-is', without any express or implied warranty.
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In no event will the authors be held liable for any damages arising from the use of this software.
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Permission is granted to anyone to use this software for any purpose,
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including commercial applications, and to alter it and redistribute it freely,
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subject to the following restrictions:
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1. The origin of this software must not be misrepresented; you must not claim that you wrote the original software. If you use this software in a product, an acknowledgment in the product documentation would be appreciated but is not required.
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2. Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.
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3. This notice may not be removed or altered from any source distribution.
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*/
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#ifndef GRAHAM_SCAN_2D_CONVEX_HULL_H
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#define GRAHAM_SCAN_2D_CONVEX_HULL_H
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#include "btVector3.h"
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#include "btAlignedObjectArray.h"
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struct GrahamVector3 : public btVector3
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{
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GrahamVector3(const btVector3& org, int orgIndex)
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: btVector3(org),
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m_orgIndex(orgIndex)
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{
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}
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btScalar m_angle;
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int m_orgIndex;
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};
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struct btAngleCompareFunc
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{
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btVector3 m_anchor;
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btAngleCompareFunc(const btVector3& anchor)
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: m_anchor(anchor)
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{
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}
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bool operator()(const GrahamVector3& a, const GrahamVector3& b) const
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{
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if (a.m_angle != b.m_angle)
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return a.m_angle < b.m_angle;
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else
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{
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btScalar al = (a - m_anchor).length2();
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btScalar bl = (b - m_anchor).length2();
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if (al != bl)
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return al < bl;
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else
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{
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return a.m_orgIndex < b.m_orgIndex;
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}
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}
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}
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};
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inline void GrahamScanConvexHull2D(btAlignedObjectArray<GrahamVector3>& originalPoints, btAlignedObjectArray<GrahamVector3>& hull, const btVector3& normalAxis)
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{
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btVector3 axis0, axis1;
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btPlaneSpace1(normalAxis, axis0, axis1);
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if (originalPoints.size() <= 1)
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{
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for (int i = 0; i < originalPoints.size(); i++)
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hull.push_back(originalPoints[0]);
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return;
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}
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//step1 : find anchor point with smallest projection on axis0 and move it to first location
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for (int i = 0; i < originalPoints.size(); i++)
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{
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// const btVector3& left = originalPoints[i];
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// const btVector3& right = originalPoints[0];
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btScalar projL = originalPoints[i].dot(axis0);
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btScalar projR = originalPoints[0].dot(axis0);
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if (projL < projR)
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{
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originalPoints.swap(0, i);
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}
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}
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//also precompute angles
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originalPoints[0].m_angle = -1e30f;
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for (int i = 1; i < originalPoints.size(); i++)
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{
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btVector3 ar = originalPoints[i] - originalPoints[0];
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btScalar ar1 = axis1.dot(ar);
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btScalar ar0 = axis0.dot(ar);
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if (ar1 * ar1 + ar0 * ar0 < FLT_EPSILON)
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{
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originalPoints[i].m_angle = 0.0f;
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}
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else
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{
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originalPoints[i].m_angle = btAtan2Fast(ar1, ar0);
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}
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}
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//step 2: sort all points, based on 'angle' with this anchor
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btAngleCompareFunc comp(originalPoints[0]);
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originalPoints.quickSortInternal(comp, 1, originalPoints.size() - 1);
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int i;
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for (i = 0; i < 2; i++)
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hull.push_back(originalPoints[i]);
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//step 3: keep all 'convex' points and discard concave points (using back tracking)
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for (; i != originalPoints.size(); i++)
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{
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bool isConvex = false;
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while (!isConvex && hull.size() > 1)
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{
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btVector3& a = hull[hull.size() - 2];
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btVector3& b = hull[hull.size() - 1];
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isConvex = btCross(a - b, a - originalPoints[i]).dot(normalAxis) > 0;
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if (!isConvex)
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hull.pop_back();
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else
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hull.push_back(originalPoints[i]);
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}
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if (hull.size() == 1)
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{
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hull.push_back(originalPoints[i]);
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}
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}
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}
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#endif //GRAHAM_SCAN_2D_CONVEX_HULL_H
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