axiosengine/axios/Dynamics/Island.cs

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2012-03-19 23:57:59 +00:00
/*
* Farseer Physics Engine based on Box2D.XNA port:
* Copyright (c) 2010 Ian Qvist
*
* Box2D.XNA port of Box2D:
* Copyright (c) 2009 Brandon Furtwangler, Nathan Furtwangler
*
* Original source Box2D:
* Copyright (c) 2006-2009 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.
*/
using System;
using System.Diagnostics;
using FarseerPhysics.Common;
using FarseerPhysics.Dynamics.Contacts;
using FarseerPhysics.Dynamics.Joints;
using Microsoft.Xna.Framework;
namespace FarseerPhysics.Dynamics
{
/// <summary>
/// This is an internal class.
/// </summary>
public class Island
{
public Body[] Bodies;
public int BodyCount;
public int ContactCount;
public int JointCount;
private int _bodyCapacity;
private int _contactCapacity;
private ContactManager _contactManager;
private ContactSolver _contactSolver = new ContactSolver();
private Contact[] _contacts;
private int _jointCapacity;
private Joint[] _joints;
public float JointUpdateTime;
private const float LinTolSqr = Settings.LinearSleepTolerance * Settings.LinearSleepTolerance;
private const float AngTolSqr = Settings.AngularSleepTolerance * Settings.AngularSleepTolerance;
#if (!SILVERLIGHT)
private Stopwatch _watch = new Stopwatch();
#endif
public void Reset(int bodyCapacity, int contactCapacity, int jointCapacity, ContactManager contactManager)
{
_bodyCapacity = bodyCapacity;
_contactCapacity = contactCapacity;
_jointCapacity = jointCapacity;
BodyCount = 0;
ContactCount = 0;
JointCount = 0;
_contactManager = contactManager;
if (Bodies == null || Bodies.Length < bodyCapacity)
{
Bodies = new Body[bodyCapacity];
}
if (_contacts == null || _contacts.Length < contactCapacity)
{
_contacts = new Contact[contactCapacity * 2];
}
if (_joints == null || _joints.Length < jointCapacity)
{
_joints = new Joint[jointCapacity * 2];
}
}
public void Clear()
{
BodyCount = 0;
ContactCount = 0;
JointCount = 0;
}
private float _tmpTime;
public void Solve(ref TimeStep step, ref Vector2 gravity)
{
// Integrate velocities and apply damping.
for (int i = 0; i < BodyCount; ++i)
{
Body b = Bodies[i];
if (b.BodyType != BodyType.Dynamic)
{
continue;
}
// Integrate velocities.
// FPE 3 only - Only apply gravity if the body wants it.
if (b.IgnoreGravity)
{
b.LinearVelocityInternal.X += step.dt * (b.InvMass * b.Force.X);
b.LinearVelocityInternal.Y += step.dt * (b.InvMass * b.Force.Y);
b.AngularVelocityInternal += step.dt * b.InvI * b.Torque;
}
else
{
b.LinearVelocityInternal.X += step.dt * (gravity.X + b.InvMass * b.Force.X);
b.LinearVelocityInternal.Y += step.dt * (gravity.Y + b.InvMass * b.Force.Y);
b.AngularVelocityInternal += step.dt * b.InvI * b.Torque;
}
// Apply damping.
// ODE: dv/dt + c * v = 0
// Solution: v(t) = v0 * exp(-c * t)
// Time step: v(t + dt) = v0 * exp(-c * (t + dt)) = v0 * exp(-c * t) * exp(-c * dt) = v * exp(-c * dt)
// v2 = exp(-c * dt) * v1
// Taylor expansion:
// v2 = (1.0f - c * dt) * v1
b.LinearVelocityInternal *= MathUtils.Clamp(1.0f - step.dt * b.LinearDamping, 0.0f, 1.0f);
b.AngularVelocityInternal *= MathUtils.Clamp(1.0f - step.dt * b.AngularDamping, 0.0f, 1.0f);
}
// Partition contacts so that contacts with static bodies are solved last.
int i1 = -1;
for (int i2 = 0; i2 < ContactCount; ++i2)
{
Fixture fixtureA = _contacts[i2].FixtureA;
Fixture fixtureB = _contacts[i2].FixtureB;
Body bodyA = fixtureA.Body;
Body bodyB = fixtureB.Body;
bool nonStatic = bodyA.BodyType != BodyType.Static && bodyB.BodyType != BodyType.Static;
if (nonStatic)
{
++i1;
//TODO: Only swap if they are not the same? see http://code.google.com/p/box2d/issues/detail?id=162
Contact tmp = _contacts[i1];
_contacts[i1] = _contacts[i2];
_contacts[i2] = tmp;
}
}
// Initialize velocity constraints.
_contactSolver.Reset(_contacts, ContactCount, step.dtRatio, Settings.EnableWarmstarting);
_contactSolver.InitializeVelocityConstraints();
if (Settings.EnableWarmstarting)
{
_contactSolver.WarmStart();
}
#if (!SILVERLIGHT)
if (Settings.EnableDiagnostics)
{
_watch.Start();
_tmpTime = 0;
}
#endif
for (int i = 0; i < JointCount; ++i)
{
if (_joints[i].Enabled)
_joints[i].InitVelocityConstraints(ref step);
}
#if (!SILVERLIGHT)
if (Settings.EnableDiagnostics)
{
_tmpTime += _watch.ElapsedTicks;
}
#endif
// Solve velocity constraints.
for (int i = 0; i < Settings.VelocityIterations; ++i)
{
#if (!SILVERLIGHT)
if (Settings.EnableDiagnostics)
_watch.Start();
#endif
for (int j = 0; j < JointCount; ++j)
{
Joint joint = _joints[j];
if (!joint.Enabled)
continue;
joint.SolveVelocityConstraints(ref step);
joint.Validate(step.inv_dt);
}
#if (!SILVERLIGHT)
if (Settings.EnableDiagnostics)
{
_watch.Stop();
_tmpTime += _watch.ElapsedTicks;
_watch.Reset();
}
#endif
_contactSolver.SolveVelocityConstraints();
}
// Post-solve (store impulses for warm starting).
_contactSolver.StoreImpulses();
// Integrate positions.
for (int i = 0; i < BodyCount; ++i)
{
Body b = Bodies[i];
if (b.BodyType == BodyType.Static)
{
continue;
}
// Check for large velocities.
float translationX = step.dt * b.LinearVelocityInternal.X;
float translationY = step.dt * b.LinearVelocityInternal.Y;
float result = translationX * translationX + translationY * translationY;
if (result > Settings.MaxTranslationSquared)
{
float sq = (float)Math.Sqrt(result);
float ratio = Settings.MaxTranslation / sq;
b.LinearVelocityInternal.X *= ratio;
b.LinearVelocityInternal.Y *= ratio;
}
float rotation = step.dt * b.AngularVelocityInternal;
if (rotation * rotation > Settings.MaxRotationSquared)
{
float ratio = Settings.MaxRotation / Math.Abs(rotation);
b.AngularVelocityInternal *= ratio;
}
// Store positions for continuous collision.
b.Sweep.C0.X = b.Sweep.C.X;
b.Sweep.C0.Y = b.Sweep.C.Y;
b.Sweep.A0 = b.Sweep.A;
// Integrate
b.Sweep.C.X += step.dt * b.LinearVelocityInternal.X;
b.Sweep.C.Y += step.dt * b.LinearVelocityInternal.Y;
b.Sweep.A += step.dt * b.AngularVelocityInternal;
// Compute new transform
b.SynchronizeTransform();
// Note: shapes are synchronized later.
}
// Iterate over constraints.
for (int i = 0; i < Settings.PositionIterations; ++i)
{
bool contactsOkay = _contactSolver.SolvePositionConstraints(Settings.ContactBaumgarte);
bool jointsOkay = true;
#if (!SILVERLIGHT)
if (Settings.EnableDiagnostics)
_watch.Start();
#endif
for (int j = 0; j < JointCount; ++j)
{
Joint joint = _joints[j];
if (!joint.Enabled)
continue;
bool jointOkay = joint.SolvePositionConstraints();
jointsOkay = jointsOkay && jointOkay;
}
#if (!SILVERLIGHT)
if (Settings.EnableDiagnostics)
{
_watch.Stop();
_tmpTime += _watch.ElapsedTicks;
_watch.Reset();
}
#endif
if (contactsOkay && jointsOkay)
{
// Exit early if the position errors are small.
break;
}
}
#if (!SILVERLIGHT)
if (Settings.EnableDiagnostics)
{
JointUpdateTime = _tmpTime;
}
#endif
Report(_contactSolver.Constraints);
if (Settings.AllowSleep)
{
float minSleepTime = Settings.MaxFloat;
for (int i = 0; i < BodyCount; ++i)
{
Body b = Bodies[i];
if (b.BodyType == BodyType.Static)
{
continue;
}
if ((b.Flags & BodyFlags.AutoSleep) == 0)
{
b.SleepTime = 0.0f;
minSleepTime = 0.0f;
}
if ((b.Flags & BodyFlags.AutoSleep) == 0 ||
b.AngularVelocityInternal * b.AngularVelocityInternal > AngTolSqr ||
Vector2.Dot(b.LinearVelocityInternal, b.LinearVelocityInternal) > LinTolSqr)
{
b.SleepTime = 0.0f;
minSleepTime = 0.0f;
}
else
{
b.SleepTime += step.dt;
minSleepTime = Math.Min(minSleepTime, b.SleepTime);
}
}
if (minSleepTime >= Settings.TimeToSleep)
{
for (int i = 0; i < BodyCount; ++i)
{
Body b = Bodies[i];
b.Awake = false;
}
}
}
}
internal void SolveTOI(ref TimeStep subStep)
{
_contactSolver.Reset(_contacts, ContactCount, subStep.dtRatio, false);
// Solve position constraints.
const float kTOIBaumgarte = 0.75f;
for (int i = 0; i < Settings.TOIPositionIterations; ++i)
{
bool contactsOkay = _contactSolver.SolvePositionConstraints(kTOIBaumgarte);
if (contactsOkay)
{
break;
}
if (i == Settings.TOIPositionIterations - 1)
{
i += 0;
}
}
// Leap of faith to new safe state.
for (int i = 0; i < BodyCount; ++i)
{
Body body = Bodies[i];
body.Sweep.A0 = body.Sweep.A;
body.Sweep.C0 = body.Sweep.C;
}
// No warm starting is needed for TOI events because warm
// starting impulses were applied in the discrete solver.
_contactSolver.InitializeVelocityConstraints();
// Solve velocity constraints.
for (int i = 0; i < Settings.TOIVelocityIterations; ++i)
{
_contactSolver.SolveVelocityConstraints();
}
// Don't store the TOI contact forces for warm starting
// because they can be quite large.
// Integrate positions.
for (int i = 0; i < BodyCount; ++i)
{
Body b = Bodies[i];
if (b.BodyType == BodyType.Static)
{
continue;
}
// Check for large velocities.
float translationx = subStep.dt * b.LinearVelocityInternal.X;
float translationy = subStep.dt * b.LinearVelocityInternal.Y;
float dot = translationx * translationx + translationy * translationy;
if (dot > Settings.MaxTranslationSquared)
{
float norm = 1f / (float)Math.Sqrt(dot);
float value = Settings.MaxTranslation * subStep.inv_dt;
b.LinearVelocityInternal.X = value * (translationx * norm);
b.LinearVelocityInternal.Y = value * (translationy * norm);
}
float rotation = subStep.dt * b.AngularVelocity;
if (rotation * rotation > Settings.MaxRotationSquared)
{
if (rotation < 0.0)
{
b.AngularVelocityInternal = -subStep.inv_dt * Settings.MaxRotation;
}
else
{
b.AngularVelocityInternal = subStep.inv_dt * Settings.MaxRotation;
}
}
// Integrate
b.Sweep.C.X += subStep.dt * b.LinearVelocityInternal.X;
b.Sweep.C.Y += subStep.dt * b.LinearVelocityInternal.Y;
b.Sweep.A += subStep.dt * b.AngularVelocityInternal;
// Compute new transform
b.SynchronizeTransform();
// Note: shapes are synchronized later.
}
Report(_contactSolver.Constraints);
}
public void Add(Body body)
{
Debug.Assert(BodyCount < _bodyCapacity);
Bodies[BodyCount++] = body;
}
public void Add(Contact contact)
{
Debug.Assert(ContactCount < _contactCapacity);
_contacts[ContactCount++] = contact;
}
public void Add(Joint joint)
{
Debug.Assert(JointCount < _jointCapacity);
_joints[JointCount++] = joint;
}
private void Report(ContactConstraint[] constraints)
{
if (_contactManager == null)
return;
for (int i = 0; i < ContactCount; ++i)
{
Contact c = _contacts[i];
if (c.FixtureA.AfterCollision != null)
c.FixtureA.AfterCollision(c.FixtureA, c.FixtureB, c);
if (c.FixtureB.AfterCollision != null)
c.FixtureB.AfterCollision(c.FixtureB, c.FixtureA, c);
if (_contactManager.PostSolve != null)
{
ContactConstraint cc = constraints[i];
_contactManager.PostSolve(c, cc);
}
}
}
}
}