Added Box2D

external/Box2D-2.3.1/Contributions/Enhancements/Controllers/b2TensorDampingController.h

@@ -0,0 +1,69 @@
+/*
+* Copyright (c) 2006-2007 Erin Catto http://www.gphysics.com
+*
+* This software is provided 'as-is', without any express or implied
+* warranty.  In no event will the authors be held liable for any damages
+* arising from the use of this software.
+* Permission is granted to anyone to use this software for any purpose,
+* including commercial applications, and to alter it and redistribute it
+* freely, subject to the following restrictions:
+* 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.
+* 2. Altered source versions must be plainly marked as such, and must not be
+* misrepresented as being the original software.
+* 3. This notice may not be removed or altered from any source distribution.
+*/
+
+#ifndef B2_TENSORDAMPINGCONTROLLER_H
+#define B2_TENSORDAMPINGCONTROLLER_H
+
+#include "b2Controller.h"
+
+class b2TensorDampingControllerDef;
+
+/// Applies top down linear damping to the controlled bodies
+/// The damping is calculated by multiplying velocity by a matrix in local co-ordinates.
+class b2TensorDampingController : public b2Controller{
+public:
+	/// Tensor to use in damping model
+	b2Mat22 T;
+	/*Some examples (matrixes in format (row1; row2) )
+	(-a 0;0 -a)		Standard isotropic damping with strength a
+	(0 a;-a 0)		Electron in fixed field - a force at right angles to velocity with proportional magnitude
+	(-a 0;0 -b)		Differing x and y damping. Useful e.g. for top-down wheels.
+	*/
+	//By the way, tensor in this case just means matrix, don't let the terminology get you down.
+
+	/// Set this to a positive number to clamp the maximum amount of damping done.
+	float32 maxTimestep;
+	// Typically one wants maxTimestep to be 1/(max eigenvalue of T), so that damping will never cause something to reverse direction
+
+	/// @see b2Controller::Step
+	void Step(const b2TimeStep& step);
+
+protected:
+	void Destroy(b2BlockAllocator* allocator);
+
+private:
+	friend class b2TensorDampingControllerDef;
+	b2TensorDampingController(const b2TensorDampingControllerDef* def);
+
+};
+
+/// This class is used to build tensor damping controllers
+class b2TensorDampingControllerDef : public b2ControllerDef
+{
+public:
+	/// Tensor to use in damping model
+	b2Mat22 T;
+	/// Set this to a positive number to clamp the maximum amount of damping done.
+	float32 maxTimestep;
+	/// Sets damping independantly along the x and y axes
+	void SetAxisAligned(float32 xDamping,float32 yDamping);
+private:
+	b2TensorDampingController* Create(b2BlockAllocator* allocator) const;
+};
+
+#endif