Exemplo n.º 1
0
        public static void Initialize(string windowType)
        {
            Testbed.Initialize();

            if (windowType == "?" || windowType == "h" || windowType == "help")
            {
                MessageBox.Show(
                    "editor - run as physical editor\n" +
                    "coe - run as conservation of energy demo\n" +
                    "testbed - run as physical testbed\n" +
                    "help - show this text",
                    "LSM Prototype commands"
                    );
            }
            else if (windowType == "editor")
            {
                editorWindow = new EditorWindow();
                window       = editorWindow;
            }
            else if (windowType == "coe")
            {
                coeWindow = new CoeWindow();
                window    = coeWindow;
            }
            else if (windowType == "main")
            {
                window = new MainWindow();
            }
            else
            {
                testbedWindow = new TestbedWindow();
                window        = testbedWindow;
            }
        }
Exemplo n.º 2
0
        public TestbedWindow()
        {
            InitializeComponent();

            // TODO: remove Testbed-related logic from here

            Testbed.world.bodyWallRepulse.SetDimensions(renderBox.Width, renderBox.Height);
            Testbed.wallForce.SetDimensions(renderBox.Width, renderBox.Height);

            for (int i = 0; i < Testbed.world.bodies.Count; ++i)
            {
                Testbed.MakeDataBindingForBody(this, Testbed.world.bodies[i], i);
            }

            statusBox.PostMessage(Color.Green, "Simulation started");
        }
Exemplo n.º 3
0
        private void TimerTick(object sender, EventArgs e)
        {
            // TODO: remove Testbed-related logic from here

            // PreUpdate interaction services
            foreach (IService service in Testbed.interactionServices)
            {
                service.PreUpdate();
            }

            // Update physics
            pauseStepFrame++;
            Testbed.paused = true;

            if (pauseStepButton.Capture && pauseStepFrame % 20 == 0 && pauseStepFrame > 0)
            {
                Testbed.Update();
            }
            else if (runButton.Capture || runCheckBox.Checked)
            {
                Testbed.paused = false;
                Testbed.Update();
            }
            else
            {
                // Apply the drag force, even if we are paused
                foreach (LsmBody body in Testbed.world.bodies) // TODO: fix this HACK
                {
                    Testbed.dragParticle.ApplyForce(body.particles);
                }
            }

            // PostUpdate interaction services
            foreach (IService service in Testbed.interactionServices)
            {
                service.PostUpdate();
            }

            // Update presentation
            this.Render();
            UpdatePanels();
        }
        public void Render()
        {
            Gl.glMatrixMode(Gl.GL_PROJECTION);
            Gl.glLoadIdentity();

            Gl.glOrtho(
                //Testbed.screenZoom * Testbed.screenTranslate.X, Testbed.screenZoom * (Testbed.screenTranslate.X + (double)currentWidth),
                //Testbed.screenZoom * Testbed.screenTranslate.Y, Testbed.screenZoom * (Testbed.screenTranslate.Y + (double)currentHeight),
                Testbed.screenTranslate.X, Testbed.screenTranslate.X + Testbed.screenZoom * ((double)currentWidth),
                Testbed.screenTranslate.Y, Testbed.screenTranslate.Y + Testbed.screenZoom * ((double)currentHeight),
                -10.0, 10.0
                );

            renderBox.Invalidate(true);

            Gl.glClear(Gl.GL_COLOR_BUFFER_BIT);

            Testbed.Render();

            Gl.glFlush();
        }
Exemplo n.º 5
0
        private CollisionSubframeBuffer GenerateContact_Reflection(
            Particle particle, Particle origin, Particle neighbor, Particle.CCDDebugInfo ccd, double ccdCollisionTime, double timeCoefficientPrediction,
            CollisionSubframeBuffer subframeToAdd
            )
        {
            double  alpha = ccd.coordinateOfPointOnEdge;
            Vector2 velocityEdgeCollisionPoint = origin.v + (neighbor.v - origin.v) * alpha;
            Vector2 velocityPointRelativeEdge  = particle.v - velocityEdgeCollisionPoint;

            // compute velocity reflection relativly moving edge
            Vector2 reflectSurface = ccd.edge.end - ccd.edge.start;
            Vector2 reflectNormal  = new Vector2(-reflectSurface.Y, reflectSurface.X);

            if (reflectNormal.Dot(velocityPointRelativeEdge) < 0)
            {
                reflectNormal = -reflectNormal;
            }

            Vector2 newVelocity =
                velocityPointRelativeEdge - (1.0 + coefficientElasticity) * reflectNormal * (reflectNormal.Dot(velocityPointRelativeEdge) / reflectNormal.LengthSq());

            if (ccdCollisionTime <= 0.0)
            {
                Testbed.PostMessage(System.Drawing.Color.Red, "timeCoefficient = 0");                          // Zero-Distance not allowed // DEBUG
            }
            double newTimeCoefficient = timeCoefficientPrediction * ccdCollisionTime;

            newTimeCoefficient -= epsilon / newVelocity.Length(); // try to prevent Zero-Distances // HACK // TODO: check Length() > epsilon
            if (newTimeCoefficient < 0.0)
            {
                newTimeCoefficient = 0.0;              // don't move particle toward edge - just reflect velocity
            }
            newVelocity += velocityEdgeCollisionPoint; // newVelocity should be in global coordinates

            subframeToAdd.vParticle       = newVelocity;
            subframeToAdd.timeCoefficient = newTimeCoefficient;
            return(subframeToAdd);
        }
Exemplo n.º 6
0
        public bool DoFracture(ref Particle other, ref Particle me)
        {
            bool somethingBroke = false;

            double len  = (other.goal - goal).Length();
            double rest = (other.x0 - x0).Length();
            double off  = Math.Abs((len / rest) - 1.0);

            if (off > LsmBody.fractureLengthTolerance)
            {
                somethingBroke = true;
                Testbed.PostMessage("Length fracture: Rest = " + rest + ", actual = " + len);
            }

            if (!somethingBroke)
            {
                Vector2 a = new Vector2(other.R[0, 0], other.R[1, 0]);
                Vector2 b = new Vector2(R[0, 0], R[1, 0]);
                a.Normalize();
                b.Normalize();
                double angleDifference = Math.Acos(a.Dot(b));
                if (angleDifference > LsmBody.fractureAngleTolerance)
                {
                    somethingBroke = true;
                    Testbed.PostMessage("Angle fracture: angle difference = " + angleDifference);
                }
            }

            if (somethingBroke)
            {
                Particle saved = other;
                me    = null;
                other = null;

                // Check if the chunks are still connected
                Queue <Particle> edge  = new Queue <Particle>();
                List <Particle>  found = new List <Particle>();
                edge.Enqueue(this);
                bool connected = false;
                while (edge.Count > 0)
                {
                    Particle p = edge.Dequeue();
                    if (!found.Contains(p))
                    {
                        found.Add(p);
                        if (p == saved)
                        {
                            // Connected
                            connected = true;
                            break;
                        }
                        if (p.xPos != null)
                        {
                            edge.Enqueue(p.xPos);
                        }
                        if (p.xNeg != null)
                        {
                            edge.Enqueue(p.xNeg);
                        }
                        if (p.yPos != null)
                        {
                            edge.Enqueue(p.yPos);
                        }
                        if (p.yNeg != null)
                        {
                            edge.Enqueue(p.yNeg);
                        }
                    }
                }
                if (connected == false)
                {
                    // The chunks broke - there are now two separate chunks (maximally connected subgraphs)
                    chunk.particles.Clear();
                    chunk.particles.AddRange(found);
                    chunk.CalculateInvariants();

                    Chunk newChunk = new Chunk();

                    edge.Clear();
                    found.Clear();
                    edge.Enqueue(saved);
                    while (edge.Count > 0)
                    {
                        Particle p = edge.Dequeue();
                        if (!found.Contains(p))
                        {
                            found.Add(p);
                            p.chunk = newChunk;
                            if (p.xPos != null)
                            {
                                edge.Enqueue(p.xPos);
                            }
                            if (p.xNeg != null)
                            {
                                edge.Enqueue(p.xNeg);
                            }
                            if (p.yPos != null)
                            {
                                edge.Enqueue(p.yPos);
                            }
                            if (p.yNeg != null)
                            {
                                edge.Enqueue(p.yNeg);
                            }
                        }
                    }

                    newChunk.particles.AddRange(found);
                    newChunk.CalculateInvariants();
                    body.chunks.Add(newChunk);

                    Testbed.PostMessage("Chunk broken: the original chunk now has " + chunk.particles.Count + " particles, the new chunk has " + newChunk.particles.Count + " particles.");
                    Testbed.PostMessage("Number of chunks / particles: " + body.chunks.Count + " / " + body.particles.Count);
                }
            }

            return(somethingBroke);
        }
Exemplo n.º 7
0
        // NOTE: This does NOT reuse sub-summations, and therefore is O(w^3) rather than O(1) as can be attained (see Readme.txt)
        public void ShapeMatch()
        {
            if (M == 0)
            {
                return;
            }

            // Calculate center of mass
            Vector2 c = new Vector2();

            foreach (Particle p in particles)
            {
                c += p.PerRegionMass * p.x;
            }
            c /= M;

            // Calculate A = Sum( m~ (xi - cr)(xi0 - cr0)^T ) - Eqn. 10
            Matrix2x2 A = Matrix2x2.ZERO;

            foreach (Particle p in particles)
            {
                A += p.PerRegionMass * Matrix2x2.MultiplyWithTranspose(p.x - c, p.x0 - c0);
            }

            // Polar decompose
            Matrix2x2 S = new Matrix2x2();

            R = A.ExtractRotation();

            if (double.IsNaN(R[0, 0]))
            {
                R = Matrix2x2.IDENTITY;
            }

            // Check for and fix inverted shape matching
            if (R.Determinant() < 0)
            {
                R = R * -1;
            }

            // Calculate o, the remaining part of Tr
            o = c + R * (-c0);

            // Add our influence to the particles' goal positions
            Vector2 sumAppliedForces = Vector2.ZERO;

            foreach (Particle p in particles)
            {
                // Figure out the goal position according to this region, Tr * p.x0
                Vector2 particleGoalPosition = o + R * p.x0;

                p.goal += p.PerRegionMass * particleGoalPosition;
                p.R    += p.PerRegionMass * R;

                // For checking only
                sumAppliedForces += p.PerRegionMass * (particleGoalPosition - p.x);
            }

            // Error check
            if (sumAppliedForces.Length() > 0.001)
            {
                Testbed.PostMessage(Color.Red, "Shape matching region's forces did not sum to zero!");
            }
        }
Exemplo n.º 8
0
        private CollisionSubframeBuffer GenerateContact_ImpulseConservation(
            Particle particle, Particle origin, Particle neighbor, Particle.CCDDebugInfo ccd, double ccdCollisionTime, double timeCoefficientPrediction,
            CollisionSubframeBuffer subframeToAdd
            )
        {
            double  alpha        = ccd.coordinateOfPointOnEdge;
            Vector2 edge         = neighbor.x - origin.x;
            double  edgeLengthSq = edge.LengthSq();

            if (edgeLengthSq < epsilon) // don't collide with too short edges // TODO: figure out how to solve this case
            {
                return(null);
            }

            //  1. find mass of EdgeCollisionPoint:
            //    double massEdgeCollisionPoint = origin.mass + neighbor.mass; // ??? // mass of virtual point // alternative:
            //                                                                                                      m = origin.mass,                    alpha = 0
            //                                                                                                      m = origin.mass + neighbor.mass,    alpha = neighbor.mass/(origin.mass + neighbor.mass)
            //                                                                                                      m = neighbor.mass,                  alpha = 1
            //
            //  2. use rule of impact for 2 bodies - it defines normal components of velocity of EdgeCollisionPoint (v2) and collisionParticle (v1). tangent components of velocities have no changes.
            //          v1new = v1 - m2*(v1-v2)*(1+k)/(m1+m2)
            //          v2new = v2 + m1*(v1-v2)*(1+k)/(m1+m2)
            //
            //      k is a coefficient of elasticity, it belongs to [0..1]
            //      note that system lose some kinetic energy: dT = (0.5*(1-k^2)*m1*m2*(v1-v2)^2)/(m1+m2)
            //
            //  3. find new origin.v and new neighbor.v (origin.v' and neighbor.v') from found velocity of EdgeCollisionPoint
            //          // Rule of distribution for the EdgeCollisionPoint velocity on origin and neighbor
            //          velocityEdgeCollisionPoint' = origin.v' + (neighbor.v' - origin.v') * ccd.coordinateOfPointOnEdge				// linear velocity distribution on edge
            //          massEdgeCollisionPoint * velocityEdgeCollisionPoint' = origin.mass * origin.v' + neighbor.mass * neighbor.v'	// impulse of virtual point = sum of impulses of edge-vertex points
            //																															//		to distribute velocity from virtual points to edge vertices with impulse conservation

            double alphaCenterOfMass = neighbor.mass / (origin.mass + neighbor.mass);
            double betaLeft          = alpha / alphaCenterOfMass;
            double betaRight         = (alpha - alphaCenterOfMass) / (1.0 - alphaCenterOfMass);

            /**/
            double massEdgeCollisionPoint = origin.mass + neighbor.mass;        // simple mass approach

            /*/
             * double massEdgeCollisionPoint = alpha < alphaCenterOfMass ?       // complex mass approach
             *  origin.mass * (1.0 - betaLeft) + (origin.mass + neighbor.mass) * betaLeft :
             *  (origin.mass + neighbor.mass) * (1.0 - betaRight ) + neighbor.mass * betaRight;
             * /**/

            Vector2 velocityEdgeCollisionPoint         = origin.v + (neighbor.v - origin.v) * alpha;
            Vector2 velocityEdgeCollisionPoint_Tangent = (velocityEdgeCollisionPoint.Dot(edge) / edgeLengthSq) * edge;
            Vector2 velocityEdgeCollisionPoint_Normal  = velocityEdgeCollisionPoint - velocityEdgeCollisionPoint_Tangent;
            Vector2 velocityParticle_Tangent           = (particle.v.Dot(edge) / edgeLengthSq) * edge;
            Vector2 velocityParticle_Normal            = particle.v - velocityParticle_Tangent;

            Vector2 newVelocityECP_Tangent = velocityEdgeCollisionPoint_Tangent; // it means that we have no perticle-edge friction // TODO: implement some friction model
            Vector2 newVelocityECP_Normal  = velocityEdgeCollisionPoint_Normal +
                                             ((1.0 + coefficientElasticity) * particle.mass / (particle.mass + massEdgeCollisionPoint)) * (velocityParticle_Normal - velocityEdgeCollisionPoint_Normal);
            Vector2 newVelocityECP = newVelocityECP_Tangent + newVelocityECP_Normal;

            Vector2 newVelocityParticle_Tangent = velocityParticle_Tangent; // it means that we have no perticle-edge friction // TODO: implement some friction model
            Vector2 newVelocityParticle_Normal  = velocityParticle_Normal -
                                                  ((1.0 + coefficientElasticity) * massEdgeCollisionPoint / (particle.mass + massEdgeCollisionPoint)) * (velocityParticle_Normal - velocityEdgeCollisionPoint_Normal);
            Vector2 newVelocityParticle = newVelocityParticle_Tangent + newVelocityParticle_Normal;

            if (ccdCollisionTime <= 0.0)
            {
                Testbed.PostMessage(System.Drawing.Color.Red, "timeCoefficient = 0");                          // Zero-Distance not allowed // DEBUG
            }
            double newTimeCoefficient = timeCoefficientPrediction * ccdCollisionTime;

            newTimeCoefficient -= epsilon / (newVelocityParticle - newVelocityECP).Length(); // try to prevent Zero-Distances // HACK // TODO: check Length() > epsilon
            if (newTimeCoefficient < 0.0)
            {
                newTimeCoefficient = 0.0;                           // don't move particle toward edge - just reflect velocity
            }
            Vector2 newVelocityOrigin = alpha < alphaCenterOfMass ?
                                        newVelocityECP * (1.0 - betaLeft) + (origin.v + newVelocityECP - velocityEdgeCollisionPoint) * betaLeft :
                                        (origin.v + newVelocityECP - velocityEdgeCollisionPoint) * (1.0 - betaRight) + origin.v * betaRight;
            Vector2 newVelocityNeighbor = alpha < alphaCenterOfMass ?
                                          neighbor.v * (1.0 - betaLeft) + (neighbor.v + newVelocityECP - velocityEdgeCollisionPoint) * betaLeft :
                                          (neighbor.v + newVelocityECP - velocityEdgeCollisionPoint) * (1.0 - betaRight) + newVelocityECP * betaRight;

            subframeToAdd.vParticle       = newVelocityParticle;
            subframeToAdd.vEdgeStart      = newVelocityOrigin;
            subframeToAdd.vEdgeEnd        = newVelocityNeighbor;
            subframeToAdd.timeCoefficient = newTimeCoefficient;
            return(subframeToAdd);
        }

        private void CheckParticleEdge_D2D(
            ref List <Particle.CCDDebugInfo> ccds,
            Particle particle,
            Particle origin, Particle neighbor,
            ref List <CollisionSubframeBuffer> collisionBuffer, double timeCoefficientPrediction,
            CollisionSubframeBuffer subframeToAdd
            )
        {
            // TODO: avoid code coping (see below)
            Vector2 pos      = particle.x;
            Vector2 velocity = particle.v;
            Vector2 posNext  = pos + velocity * timeCoefficientPrediction;

            // swept collision for body
            LineSegment edge     = new LineSegment(origin.x, neighbor.x);
            LineSegment edgeNext = new LineSegment(edge.start + origin.v * timeCoefficientPrediction, edge.end + neighbor.v * timeCoefficientPrediction);

            EdgePointCCDSolver.SolverInput solverInput = new EdgePointCCDSolver.SolverInput(edge, edgeNext, pos, posNext);
            double?ccdCollisionTime = EdgePointCCDSolver.Solve(solverInput);

            if (ccdCollisionTime != null)
            {
                Particle.CCDDebugInfo   ccd     = GenerateDebugInfo(solverInput, ccdCollisionTime.Value);
                CollisionSubframeBuffer contact = // TODO: use the Rule of conservative impulse to handle this case. Simple reflection rule is not effective here.
                                                  GenerateContact_ImpulseConservation(
                    // GenerateContact_Reflection(
                    particle, origin, neighbor, ccd, ccdCollisionTime.Value, timeCoefficientPrediction, subframeToAdd
                    );
                if (contact != null)
                {
                    collisionBuffer.Add(contact);
                }
                ccds.Add(ccd);

                if (LsmBody.pauseOnBodyBodyCollision)
                {
                    Testbed.Paused = true;
                }
            }
        }

        Particle.CCDDebugInfo GenerateDebugInfo(EdgePointCCDSolver.SolverInput solverInput, double time) // DEBUG
        {
            Particle.CCDDebugInfo ccd = new Particle.CCDDebugInfo(
                solverInput.currentPoint + (solverInput.nextPoint - solverInput.currentPoint) * time,
                new LineSegment(
                    solverInput.currentEdge.start + (solverInput.nextEdge.start - solverInput.currentEdge.start) * time,
                    solverInput.currentEdge.end + (solverInput.nextEdge.end - solverInput.currentEdge.end) * time
                    )
                );
            return(ccd);
        }

        private void CheckParticleEdge_D2F(
            ref List <Particle.CCDDebugInfo> ccds,
            Particle particle,
            Particle origin, Particle neighbor,
            ref List <CollisionSubframeBuffer> collisionBuffer, double timeCoefficientPrediction,
            CollisionSubframeBuffer subframeToAdd
            )
        {
            // TODO: avoid code coping
            Vector2 pos      = particle.x;
            Vector2 velocity = particle.v;
            Vector2 posNext  = pos + velocity * timeCoefficientPrediction;

            // simple collision for frozen body
            CheckFrozenEdge(origin.goal, neighbor.goal, pos, posNext, velocity, ref collisionBuffer, subframeToAdd); // current edge position
        }

        private CollisionSubframeBuffer GenerateContact_ImpulseConservation_F2D(
            Particle particle, Particle origin, Particle neighbor, Particle.CCDDebugInfo ccd, double ccdCollisionTime, double timeCoefficientPrediction,
            CollisionSubframeBuffer subframeToAdd
            )
        {
            double  alpha        = ccd.coordinateOfPointOnEdge;
            Vector2 edge         = neighbor.x - origin.x;
            double  edgeLengthSq = edge.LengthSq();

            if (edgeLengthSq < epsilon)
            {
                return(null);
            }

            double alphaCenterOfMass = neighbor.mass / (origin.mass + neighbor.mass);
            double betaLeft          = alpha / alphaCenterOfMass;
            double betaRight         = (alpha - alphaCenterOfMass) / (1.0 - alphaCenterOfMass);

            /**/
            double massEdgeCollisionPoint = origin.mass + neighbor.mass;    // simple mass approach

            /*/
             * double massEdgeCollisionPoint = alpha < alphaCenterOfMass ?     // complex mass approach
             *  origin.mass * (1.0 - betaLeft) + (origin.mass + neighbor.mass) * betaLeft :
             *  (origin.mass + neighbor.mass) * (1.0 - betaRight ) + neighbor.mass * betaRight;
             * /**/

            Vector2 velocityEdgeCollisionPoint         = origin.v + (neighbor.v - origin.v) * alpha;
            Vector2 velocityEdgeCollisionPoint_Tangent = (velocityEdgeCollisionPoint.Dot(edge) / edgeLengthSq) * edge;
            Vector2 velocityEdgeCollisionPoint_Normal  = velocityEdgeCollisionPoint - velocityEdgeCollisionPoint_Tangent;
            Vector2 velocityParticle_Tangent           = Vector2.ZERO;
            Vector2 velocityParticle_Normal            = Vector2.ZERO;
            // particle.mass = infinity
            // particle.v = newVelocityParticle = Vector2.ZERO

            Vector2 newVelocityECP_Tangent = velocityEdgeCollisionPoint_Tangent; // it means that we have no particle-edge friction // TODO: implement some friction model
            Vector2 newVelocityECP_Normal  = -(1.0 + coefficientElasticity) * velocityEdgeCollisionPoint_Normal;
            Vector2 newVelocityECP         = newVelocityECP_Tangent + newVelocityECP_Normal;

            Vector2 newVelocityParticle = Vector2.ZERO;

            if (ccdCollisionTime <= 0.0)
            {
                Testbed.PostMessage(System.Drawing.Color.Red, "timeCoefficient = 0");                          // Zero-Distance not allowed // DEBUG
            }
            double newTimeCoefficient = timeCoefficientPrediction * ccdCollisionTime;

            newTimeCoefficient -= epsilon / (newVelocityParticle - newVelocityECP).Length(); // try to prevent Zero-Distances // HACK // TODO: check Length() > epsilon
            if (newTimeCoefficient < 0.0)
            {
                newTimeCoefficient = 0.0;                           // don't move particle toward edge - just reflect velocity
            }
            Vector2 newVelocityOrigin = alpha < alphaCenterOfMass ?
                                        newVelocityECP * (1.0 - betaLeft) + (origin.v + newVelocityECP - velocityEdgeCollisionPoint) * betaLeft :
                                        (origin.v + newVelocityECP - velocityEdgeCollisionPoint) * (1.0 - betaRight) + origin.v * betaRight;
            Vector2 newVelocityNeighbor = alpha < alphaCenterOfMass ?
                                          neighbor.v * (1.0 - betaLeft) + (neighbor.v + newVelocityECP - velocityEdgeCollisionPoint) * betaLeft :
                                          (neighbor.v + newVelocityECP - velocityEdgeCollisionPoint) * (1.0 - betaRight) + newVelocityECP * betaRight;

            subframeToAdd.vParticle       = newVelocityParticle;
            subframeToAdd.vEdgeStart      = newVelocityOrigin;
            subframeToAdd.vEdgeEnd        = newVelocityNeighbor;
            subframeToAdd.timeCoefficient = newTimeCoefficient;
            return(subframeToAdd);
        }
Exemplo n.º 9
0
 private void model27Button_Click(object sender, EventArgs e)
 {
     Testbed.SetModel(1, 6);
 }
Exemplo n.º 10
0
 private void model16Button_Click(object sender, EventArgs e)
 {
     Testbed.SetModel(0, 5);
 }
Exemplo n.º 11
0
 private void resetButton_Click(object sender, EventArgs e)
 {
     Testbed.Reset();
 }
Exemplo n.º 12
0
 private void pauseStepButton_MouseDown(object sender, MouseEventArgs e)
 {
     pauseStepFrame = 0;
     Testbed.Update();
 }
Exemplo n.º 13
0
        public void Update()
        {
            // update internal processes in bodies, find velocities
            foreach (LsmBody b in bodies)
            {
                if (!b.Frozen)
                {
                    foreach (IEnvironmentForce force in environmentForces)
                    {
                        if (force is WallForce && !b.UseWallForce) // HACK to apply custom forces // TODO: make correct system
                        {
                            continue;
                        }
                        force.ApplyForce(b.particles);
                    }
                    b.Smooth();
                    b.DoFracture();
                    b.UpdateParticlesVelocity();
                }
                else
                {
                    b.UpdateFrozenParticlesVelocity();
                }
            }

            // iterate subframes for collision and integration system of bodies
            List <CollisionSubframeBuffer> collisionBuffer = new List <CollisionSubframeBuffer>();
            int       iterationsCounter         = 0;  // to prevent deadlocks
            const int maxIterations             = 64; // to prevent deadlocks
            double    timeCoefficientPrediction = 1.0;
            bool      collisionFound            = false;

            do
            {
                for (int i = 0; i < bodies.Count; ++i)
                {
                    LsmBody bLeft = bodies[i];
                    if (!bLeft.Frozen && !bLeft.UseWallForce)
                    {
                        bLeft.CollideWithWall(timeCoefficientPrediction, ref collisionBuffer); // TODO: refactor to remove 'ref collisionBuffer'
                    }
                    for (int j = i + 1; j < bodies.Count; ++j)                                 // TODO: implement self-collisions for j == i.
                    {
                        LsmBody bRight = bodies[j];
                        LsmBody.CollideBodies(bLeft, bRight, timeCoefficientPrediction, ref collisionBuffer); // TODO: refactor to remove 'ref collisionBuffer'
                        LsmBody.CollideBodies(bRight, bLeft, timeCoefficientPrediction, ref collisionBuffer); // TODO: refactor to remove 'ref collisionBuffer'
                    }
                }

                double timeCoefficientIntegrate = 0.0;
                if (collisionBuffer.Count > 0)
                {
                    CollisionSubframeBuffer subframe = LsmBody.GetEarliestSubframe(collisionBuffer);    // WARNING: now we assume that in 1 time moment we have maximum 1 collision in subframe.
                    // TODO: make system ready to handle multi-collision subframes. For example, we'll need to accumulate velocity deltas for every particle and then make summation - not just direct assign of values.
                    timeCoefficientIntegrate   = subframe.timeCoefficient;
                    timeCoefficientPrediction -= subframe.timeCoefficient;

                    subframe.particle.v = subframe.vParticle;
                    if (subframe.edge != null)
                    {
                        subframe.edge.start.v = subframe.vEdgeStart;
                        subframe.edge.end.v   = subframe.vEdgeEnd;
                    }

                    collisionBuffer.Clear();
                    collisionFound = true;
                }
                else
                {
                    timeCoefficientIntegrate = timeCoefficientPrediction;
                    collisionFound           = false;
                }

                if (timeCoefficientIntegrate > 0.0)
                {
                    foreach (LsmBody b in bodies)
                    {
                        if (!b.Frozen)
                        {
                            b.UpdateParticlesPosition(timeCoefficientIntegrate);
                        }
                        else
                        {
                            b.UpdateFrozenParticlesPosition();
                        }
                    }
                }
                else
                {
                    Testbed.PostMessage(System.Drawing.Color.Yellow, "Timestep <= 0.0 while subframes iterating!"); // DEBUG
                }

                if (++iterationsCounter >= maxIterations)                                                    // to prevent deadlocks
                {
                    Testbed.PostMessage(System.Drawing.Color.Red, "Deadlock detected in HandleCollisions!"); // DEBUG
                    if (LsmBody.pauseOnDeadlock)
                    {
                        Testbed.Paused = true;
                    }
                    break;
                }
            }while (collisionFound);
        }