95 lines
2.7 KiB
C++
95 lines
2.7 KiB
C++
/*
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* Copyright (c) 2007-2009 Erin Catto http://www.box2d.org
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*
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* This software is provided 'as-is', without any express or implied
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* warranty. In no event will the authors be held liable for any damages
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* 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
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* freely, subject to the following restrictions:
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* 1. The origin of this software must not be misrepresented; you must not
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* claim that you wrote the original software. If you use this software
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* in a product, an acknowledgment in the product documentation would be
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* appreciated but is not required.
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* 2. Altered source versions must be plainly marked as such, and must not be
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* 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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#include "Box2D/Common/b2Math.h"
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const b2Vec2 b2Vec2_zero(0.0f, 0.0f);
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/// Solve A * x = b, where b is a column vector. This is more efficient
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/// than computing the inverse in one-shot cases.
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b2Vec3 b2Mat33::Solve33(const b2Vec3& b) const
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{
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float32 det = b2Dot(ex, b2Cross(ey, ez));
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if (det != 0.0f)
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{
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det = 1.0f / det;
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}
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b2Vec3 x;
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x.x = det * b2Dot(b, b2Cross(ey, ez));
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x.y = det * b2Dot(ex, b2Cross(b, ez));
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x.z = det * b2Dot(ex, b2Cross(ey, b));
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return x;
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}
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/// Solve A * x = b, where b is a column vector. This is more efficient
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/// than computing the inverse in one-shot cases.
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b2Vec2 b2Mat33::Solve22(const b2Vec2& b) const
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{
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float32 a11 = ex.x, a12 = ey.x, a21 = ex.y, a22 = ey.y;
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float32 det = a11 * a22 - a12 * a21;
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if (det != 0.0f)
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{
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det = 1.0f / det;
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}
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b2Vec2 x;
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x.x = det * (a22 * b.x - a12 * b.y);
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x.y = det * (a11 * b.y - a21 * b.x);
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return x;
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}
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///
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void b2Mat33::GetInverse22(b2Mat33* M) const
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{
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float32 a = ex.x, b = ey.x, c = ex.y, d = ey.y;
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float32 det = a * d - b * c;
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if (det != 0.0f)
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{
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det = 1.0f / det;
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}
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M->ex.x = det * d; M->ey.x = -det * b; M->ex.z = 0.0f;
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M->ex.y = -det * c; M->ey.y = det * a; M->ey.z = 0.0f;
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M->ez.x = 0.0f; M->ez.y = 0.0f; M->ez.z = 0.0f;
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}
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/// Returns the zero matrix if singular.
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void b2Mat33::GetSymInverse33(b2Mat33* M) const
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{
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float32 det = b2Dot(ex, b2Cross(ey, ez));
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if (det != 0.0f)
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{
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det = 1.0f / det;
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}
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float32 a11 = ex.x, a12 = ey.x, a13 = ez.x;
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float32 a22 = ey.y, a23 = ez.y;
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float32 a33 = ez.z;
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M->ex.x = det * (a22 * a33 - a23 * a23);
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M->ex.y = det * (a13 * a23 - a12 * a33);
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M->ex.z = det * (a12 * a23 - a13 * a22);
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M->ey.x = M->ex.y;
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M->ey.y = det * (a11 * a33 - a13 * a13);
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M->ey.z = det * (a13 * a12 - a11 * a23);
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M->ez.x = M->ex.z;
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M->ez.y = M->ey.z;
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M->ez.z = det * (a11 * a22 - a12 * a12);
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}
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