g3n-engine/physics/simulation.go

// Copyright 2016 The G3N Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package physics

import (
	"time"
	"github.com/g3n/engine/physics/equation"
	"github.com/g3n/engine/physics/solver"
	"github.com/g3n/engine/physics/constraint"
	"github.com/g3n/engine/physics/collision"
	"github.com/g3n/engine/math32"
	"github.com/g3n/engine/physics/object"
	"github.com/g3n/engine/physics/material"
)

type ICollidable interface {
	Collided() bool
	Static() bool
	//GetCollisions() []*Collision
}

type CollisionGroup struct {
	// TODO future
}

// Simulation represents a physics simulation.
type Simulation struct {
	forceFields []ForceField

	bodies      []*object.Body
	nilBodies   []int   // Array keeps track of which indices of the 'bodies' array are nil

	collisionMatrix     collision.Matrix // Boolean triangular matrix indicating which pairs of bodies are colliding
	prevCollisionMatrix collision.Matrix // CollisionMatrix from the previous step.

	allowSleep  bool                // Makes bodies go to sleep when they've been inactive
	contactEqs  []*equation.Contact // All the current contacts (instances of ContactEquation) in the world.
	frictionEqs []*equation.Friction

	quatNormalizeSkip int // How often to normalize quaternions. Set to 0 for every step, 1 for every second etc..
	                      // A larger value increases performance.
	                      // If bodies tend to explode, set to a smaller value (zero to be sure nothing can go wrong).
	quatNormalizeFast bool // Set to true to use fast quaternion normalization. It is often enough accurate to use. If bodies tend to explode, set to false.

	time float32      // The wall-clock time since simulation start
	stepnumber int    // Number of timesteps taken since start
	default_dt float32 // Default and last timestep sizes
	dt float32      // Currently / last used timestep. Is set to -1 if not available. This value is updated before each internal step, which means that it is "fresh" inside event callbacks.


	accumulator float32 // Time accumulator for interpolation. See http://gafferongames.com/game-physics/fix-your-timestep/

	broadphase *collision.Broadphase // The broadphase algorithm to use. Default is NaiveBroadphase
	narrowphase *Narrowphase // The narrowphase algorithm to use
	solver solver.ISolver    // The solver algorithm to use. Default is GSSolver

	constraints       []constraint.IConstraint  // All constraints

	materials         []*material.Material               // All added materials
	cMaterials        []*material.ContactMaterial



	//contactMaterialTable map[intPair]*ContactMaterial // Used to look up a ContactMaterial given two instances of Material.
	//defaultMaterial *Material
	defaultContactMaterial *material.ContactMaterial


	doProfiling      bool
}

// NewSimulation creates and returns a pointer to a new physics simulation.
func NewSimulation() *Simulation {

	s := new(Simulation)
	s.time = 0
	s.dt = -1
	s.default_dt = 1/60

	// Set up broadphase, narrowphase, and solver
	s.broadphase = collision.NewBroadphase()
	s.narrowphase = NewNarrowphase(s)
	s.solver = solver.NewGaussSeidel()

	//s.contactMaterialTable = make(map[intPair]*ContactMaterial)
	//s.defaultMaterial = NewMaterial
	s.defaultContactMaterial = material.NewContactMaterial()

	return s
}

// AddForceField adds a force field to the simulation.
func (s *Simulation) AddForceField(ff ForceField) {

	s.forceFields = append(s.forceFields, ff)
}

// RemoveForceField removes the specified force field from the simulation.
// Returns true if found, false otherwise.
func (s *Simulation) RemoveForceField(ff ForceField) bool {

	for pos, current := range s.forceFields {
		if current == ff {
			copy(s.forceFields[pos:], s.forceFields[pos+1:])
			s.forceFields[len(s.forceFields)-1] = nil
			s.forceFields = s.forceFields[:len(s.forceFields)-1]
			return true
		}
	}
	return false
}

// AddBody adds a body to the simulation.
func (s *Simulation) AddBody(body *object.Body) {

	// Do nothing if body already present
	for _, existingBody := range s.bodies {
		if existingBody == body {
			return // Do nothing
		}
	}

	var idx int
	nilLen := len(s.nilBodies)
	if nilLen > 0 {
		idx = s.nilBodies[nilLen]
		s.nilBodies = s.nilBodies[0:nilLen-1]
	} else {
		s.bodies = append(s.bodies, body)
	}

	body.SetIndex(idx)

	// TODO dispatch add-body event
	//s.Dispatch(AddBodyEvent, BodyEvent{body})
}

// RemoveBody removes the specified body from the simulation.
// Returns true if found, false otherwise.
func (s *Simulation) RemoveBody(body *object.Body) bool {

	for idx, current := range s.bodies {
		if current == body {
			s.bodies[idx] = nil

			// TODO dispatch remove-body event
			//s.Dispatch(AddBodyEvent, BodyEvent{body})

			return true
		}
	}

	return false
}

// Clean removes nil bodies from the bodies array, recalculates the body indices and updates the collision matrix.
//func (s *Simulation) Clean() {
//
//	// TODO Remove nil bodies from array
//	//copy(s.bodies[pos:], s.bodies[pos+1:])
//	//s.bodies[len(s.bodies)-1] = nil
//	//s.bodies = s.bodies[:len(s.bodies)-1]
//
//	// Recompute body indices (each body has a .index int property)
//	for i:=0; i<len(s.bodies); i++ {
//		s.bodies[i].SetIndex(i)
//	}
//
//	// TODO Update collision matrix
//
//}

// Bodies returns the slice of bodies under simulation.
// The slice may contain nil values!
func (s *Simulation) Bodies() []*object.Body{

	return s.bodies
}


// Step steps the simulation.
func (s *Simulation) Step(frameDelta time.Duration) {

	// Check for collisions
	//collisions := s.CheckCollisions()
	//if len(collisions) > 0 {
	//	// Backtrack to 0 penetration
	//	s.Backtrack()
	//}

	// Apply static forces/inertia/impulses (only to objects that did not collide)
	//s.applyForceFields()
	// s.applyDrag(frameDelta) // TODO

	// Apply impact forces/inertia/impulses to objects that collided
	//s.applyImpactForces(frameDelta)

	// Update object positions based on calculated final speeds
	//s.updatePositions(frameDelta)

}

// ClearForces sets all body forces in the world to zero.
func (s *Simulation) ClearForces() {

	for i:=0; i < len(s.bodies); i++ {
		s.bodies[i].ClearForces()
	}
}

// Add a constraint to the simulation.
func (s *Simulation) AddConstraint(c constraint.IConstraint) {

	s.constraints = append(s.constraints, c)
}

func (s *Simulation) RemoveConstraint(c constraint.IConstraint) {

	// TODO
}

func (s *Simulation) AddMaterial(mat *material.Material) {

	s.materials = append(s.materials, mat)
}

func (s *Simulation) RemoveMaterial(mat *material.Material) {

	// TODO
}

// Adds a contact material to the simulation
func (s *Simulation) AddContactMaterial(cmat *material.ContactMaterial) {

	s.cMaterials = append(s.cMaterials, cmat)

	// TODO add contactMaterial materials to contactMaterialTable
	// s.contactMaterialTable.set(cmat.materials[0].id, cmat.materials[1].id, cmat)
}

// GetContactMaterial returns the contact material between the specified bodies.
func (s *Simulation) GetContactMaterial(bodyA, bodyB *object.Body) *material.ContactMaterial {

	var cm *material.ContactMaterial
	// TODO
	//if bodyA.material != nil && bodyB.material != nil {
	//	cm = s.contactMaterialTable.get(bodyA.material.id, bodyB.material.id)
	//	if cm == nil {
	//		cm = s.defaultContactMaterial
	//	}
	//} else {
	cm = s.defaultContactMaterial
	//}
	return cm
}


// Events =====================

type CollideEvent struct {
	body      *object.Body
	contactEq *equation.Contact
}

// TODO AddBodyEvent, RemoveBodyEvent
type ContactEvent struct {
	bodyA *object.Body
	bodyB *object.Body
}

const (
	BeginContactEvent = "physics.BeginContactEvent"
	EndContactEvent   = "physics.EndContactEvent"
	CollisionEv       = "physics.Collision"
)

// ===========================


// Note - this method alters the solution arrays
func (s *Simulation) ApplySolution(sol *solver.Solution) {

	// Add results to velocity and angular velocity of bodies
	for i := 0; i < len(s.bodies); i++ {
		s.bodies[i].ApplyVelocityDeltas(&sol.VelocityDeltas[i], &sol.AngularVelocityDeltas[i])
	}
}

// Store old collision state info
func (s *Simulation) collisionMatrixTick() {

	s.prevCollisionMatrix = s.collisionMatrix
	s.collisionMatrix = collision.NewMatrix()

	// TODO
	//s.bodyOverlapKeeper.tick()
	//s.shapeOverlapKeeper.tick()
}

// TODO read https://gafferongames.com/post/fix_your_timestep/
func (s *Simulation) internalStep(dt float32) {

	// Apply force fields and compute world normals/edges
	for _, b := range s.bodies {

		// Only apply to dynamic bodies
		if b.BodyType() == object.Dynamic {
			for _, ff := range s.forceFields {
				pos := b.Position()
				force := ff.ForceAt(&pos)
				b.ApplyForceField(&force)
			}
		}

		// Compute for the new rotation
		// TODO optimization: only need to compute the below for objects that will go through narrowphase
		b.ComputeWorldFaceNormalsAndUniqueEdges()
	}

    // TODO update subsystems ?

    // Find pairs of bodies that are potentially colliding
	pairs := s.broadphase.FindCollisionPairs(s.bodies)

	// Remove some pairs before proceeding to narrophase based on constraints' colConn property
	// which specified if constrained bodies should collide with one another
    s.prunePairs(pairs) // TODO review

	//
    s.collisionMatrixTick()

    // Generate contacts
	s.generateContacts(pairs)

    s.emitContactEvents()

    // Wake up bodies
    // TODO why not wake bodies up inside s.generateContacs when setting the WakeUpAfterNarrowphase flag?
    // Maybe there we are only looking at bodies that belong to current contact equations...
    // and need to wake up all marked bodies
    for i := 0; i < len(s.bodies); i++ {
        bi := s.bodies[i]
        if bi != nil && bi.WakeUpAfterNarrowphase() {
            bi.WakeUp()
            bi.SetWakeUpAfterNarrowphase(false)
        }
    }

    // Add user-added constraints
	userAddedEquations := 0
    for i := 0; i < len(s.constraints); i++ {
        c := s.constraints[i]
        c.Update()
        eqs := c.Equations()
        for j := 0; j < len(eqs); j++ {
			userAddedEquations++
            s.solver.AddEquation(eqs[j])
        }
    }

	// Update solve mass for all bodies
	// NOTE: This was originally inside the beginning of solver.Solve()
	if len(s.frictionEqs) + len(s.contactEqs) + userAddedEquations > 0 {
		for i := 0; i < len(s.bodies); i++ {
			s.bodies[i].UpdateEffectiveMassProperties()
		}
	}

    // Solve the constrained system
    solution := s.solver.Solve(dt, len(s.bodies))
	s.ApplySolution(solution) // Applies velocity deltas
	s.solver.ClearEquations()

    // Apply damping, see http://code.google.com/p/bullet/issues/detail?id=74 for details
    for i := 0; i < len(s.bodies); i++ {
        bi := s.bodies[i]
        if bi != nil && bi.BodyType() == object.Dynamic { // Only apply damping to dynamic bodies
			bi.ApplyDamping(dt)
        }
    }

    // TODO s.Dispatch(World_step_preStepEvent)

	// Integrate the forces into velocities into position deltas
    quatNormalize := s.stepnumber % (s.quatNormalizeSkip + 1) == 0
    for i := 0; i < len(s.bodies); i++ {
		s.bodies[i].Integrate(dt, quatNormalize, s.quatNormalizeFast)
    }
    s.ClearForces()

    // TODO s.broadphase.dirty = true ?

    // Update world time
    s.time += dt
    s.stepnumber += 1

    // TODO s.Dispatch(World_step_postStepEvent)

    // Sleeping update
    if s.allowSleep {
        for i := 0; i < len(s.bodies); i++ {
            s.bodies[i].SleepTick(s.time)
        }
    }

}

// TODO - REVIEW THIS
func (s *Simulation) prunePairs(pairs []collision.Pair) []collision.Pair {

	// TODO There is probably a bug here when the same body can have multiple constraints and appear in multiple pairs

	//// Remove constrained pairs with collideConnected == false
	//pairIdxsToRemove := []int
	//for i := 0; i < len(s.constraints); i++ {
	//	c := s.constraints[i]
	//	cBodyA := s.bodies[c.BodyA().Index()]
	//	cBodyB := s.bodies[c.BodyB().Index()]
	//	if !c.CollideConnected() {
	//		for i := range pairs {
	//			if (pairs[i].BodyA == cBodyA && pairs[i].BodyB == cBodyB) ||
	//				(pairs[i].BodyA == cBodyB && pairs[i].BodyB == cBodyA) {
	//				pairIdxsToRemove = append(pairIdxsToRemove, i)
	//
	//			}
	//		}
	//	}
	//}
	//
	//// Remove pairs
	////var prunedPairs []Pair
	//for i := range pairs {
	//	for _, idx := range pairIdxsToRemove {
	//		copy(pairs[i:], pairs[i+1:])
	//		//pairs[len(pairs)-1] = nil
	//		pairs = pairs[:len(pairs)-1]
	//	}
	//}

	return pairs
}

// generateContacts
func (s *Simulation) generateContacts(pairs []collision.Pair) {

	// Find all contacts and generate contact and friction equations (narrowphase)
	s.contactEqs, s.frictionEqs = s.narrowphase.GetContacts(pairs)

	// Add all friction equations to solver
	for i := 0; i < len(s.frictionEqs); i++ {
		s.solver.AddEquation(s.frictionEqs[i])
	}

	for k := 0; k < len(s.contactEqs); k++ {

		// Current contact
		contactEq := s.contactEqs[k]

		// Get current collision indices
		bodyA := s.bodies[contactEq.BodyA().Index()]
		bodyB := s.bodies[contactEq.BodyB().Index()]

		// TODO future: update equations with physical material properties

		s.solver.AddEquation(contactEq)

		if bodyA.AllowSleep() && bodyA.BodyType() == object.Dynamic && bodyA.SleepState() == object.Sleeping && bodyB.SleepState() == object.Awake && bodyB.BodyType() != object.Static {
			velocityB := bodyB.Velocity()
			angularVelocityB := bodyB.AngularVelocity()
			speedSquaredB := velocityB.LengthSq() + angularVelocityB.LengthSq()
			speedLimitSquaredB := math32.Pow(bodyB.SleepSpeedLimit(), 2)
			if speedSquaredB >= speedLimitSquaredB*2 {
				bodyA.SetWakeUpAfterNarrowphase(true)
			}
		}

		if bodyB.AllowSleep() && bodyB.BodyType() == object.Dynamic && bodyB.SleepState() == object.Sleeping && bodyA.SleepState() == object.Awake && bodyA.BodyType() != object.Static {
			velocityA := bodyA.Velocity()
			angularVelocityA := bodyA.AngularVelocity()
			speedSquaredA := velocityA.LengthSq() + angularVelocityA.LengthSq()
			speedLimitSquaredA := math32.Pow(bodyA.SleepSpeedLimit(), 2)
			if speedSquaredA >= speedLimitSquaredA*2 {
				bodyB.SetWakeUpAfterNarrowphase(true)
			}
		}

		// Now we know that i and j are in contact. Set collision matrix state
		s.collisionMatrix.Set(bodyA.Index(), bodyB.Index(), true)

		if s.prevCollisionMatrix.Get(bodyA.Index(), bodyB.Index()) == false {
			// First contact!
			bodyA.Dispatch(CollisionEv, &CollideEvent{bodyB, contactEq})
			bodyB.Dispatch(CollisionEv, &CollideEvent{bodyA, contactEq})
		}

		// TODO this is only for events
		//s.bodyOverlapKeeper.set(bodyA.id, bodyB.id)
		//s.shapeOverlapKeeper.set(si.id, sj.id)
	}

}

func (s *Simulation) emitContactEvents() {
	//TODO
}