@awayfl/awayfl-player/lib/Box2D/Dynamics/Joints/b2WeldJoint.ts

Flash Player emulator for executing SWF files (published for FP versions 6 and up) in javascript

import { b2Joint, b2WeldJointDef } from '../Joints';
import { b2Vec2, b2Vec3, b2Mat33, b2Math, b2Mat22 } from '../../Common/Math';
import { b2Settings } from '../../Common/b2Settings';
import { b2Body } from '../b2Body';
import { b2TimeStep } from '../b2TimeStep';

// Point-to-point constraint
// Cdot = v2 - v1
//      = v2 + cross(w2, r2) - v1 - cross(w1, r1)
// J = [-I -r1_skew I r2_skew ]
// Identity used:
// w k % (rx i + ry j) = w * (-ry i + rx j)

// Angle constraint
// Cdot = w2 - w1
// J = [0 0 -1 0 0 1]
// K = invI1 + invI2

/**
 * A weld joint essentially glues two bodies together. A weld joint may
 * distort somewhat because the island constraint solver is approximate.
 */
export class b2WeldJoint extends b2Joint {
	/** @inheritDoc */
	public GetAnchorA(): b2Vec2 {
		return this.m_bodyA.GetWorldPoint(this.m_localAnchorA);
	}

	/** @inheritDoc */
	public GetAnchorB(): b2Vec2 {
		return this.m_bodyB.GetWorldPoint(this.m_localAnchorB);
	}

	/** @inheritDoc */
	public GetReactionForce(inv_dt: number): b2Vec2 {
		return new b2Vec2(inv_dt * this.m_impulse.x, inv_dt * this.m_impulse.y);
	}

	/** @inheritDoc */
	public GetReactionTorque(inv_dt: number): number {
		return inv_dt * this.m_impulse.z;
	}

	//--------------- Internals Below -------------------

	/** @private */
	constructor(def: b2WeldJointDef) {
		super(def);

		this.m_localAnchorA.SetV(def.localAnchorA);
		this.m_localAnchorB.SetV(def.localAnchorB);
		this.m_referenceAngle = def.referenceAngle;

		this.m_impulse.SetZero();
		this.m_mass = new b2Mat33();
	}

	public InitVelocityConstraints(step: b2TimeStep): void {
		let tMat: b2Mat22;
		let tX: number;

		const bA: b2Body = this.m_bodyA;
		const bB: b2Body = this.m_bodyB;

		// Compute the effective mass matrix.
		//b2Vec2 rA = b2Mul(bA->m_xf.R, m_localAnchorA - bA->GetLocalCenter());
		tMat = bA.m_xf.R;
		let rAX: number = this.m_localAnchorA.x - bA.m_sweep.localCenter.x;
		let rAY: number = this.m_localAnchorA.y - bA.m_sweep.localCenter.y;
		tX =  (tMat.col1.x * rAX + tMat.col2.x * rAY);
		rAY = (tMat.col1.y * rAX + tMat.col2.y * rAY);
		rAX = tX;
		//b2Vec2 rB = b2Mul(bB->m_xf.R, m_localAnchorB - bB->GetLocalCenter());
		tMat = bB.m_xf.R;
		let rBX: number = this.m_localAnchorB.x - bB.m_sweep.localCenter.x;
		let rBY: number = this.m_localAnchorB.y - bB.m_sweep.localCenter.y;
		tX =  (tMat.col1.x * rBX + tMat.col2.x * rBY);
		rBY = (tMat.col1.y * rBX + tMat.col2.y * rBY);
		rBX = tX;

		// J = [-I -r1_skew I r2_skew]
		//     [ 0       -1 0       1]
		// r_skew = [-ry; rx]

		// Matlab
		// K = [ mA+r1y^2*iA+mB+r2y^2*iB,  -r1y*iA*r1x-r2y*iB*r2x,          -r1y*iA-r2y*iB]
		//     [  -r1y*iA*r1x-r2y*iB*r2x, mA+r1x^2*iA+mB+r2x^2*iB,           r1x*iA+r2x*iB]
		//     [          -r1y*iA-r2y*iB,           r1x*iA+r2x*iB,                   iA+iB]

		const mA: number = bA.m_invMass;
		const mB: number = bB.m_invMass;
		const iA: number = bA.m_invI;
		const iB: number = bB.m_invI;

		this.m_mass.col1.x = mA + mB + rAY * rAY * iA + rBY * rBY * iB;
		this.m_mass.col2.x = -rAY * rAX * iA - rBY * rBX * iB;
		this.m_mass.col3.x = -rAY * iA - rBY * iB;
		this.m_mass.col1.y = this.m_mass.col2.x;
		this.m_mass.col2.y = mA + mB + rAX * rAX * iA + rBX * rBX * iB;
		this.m_mass.col3.y = rAX * iA + rBX * iB;
		this.m_mass.col1.z = this.m_mass.col3.x;
		this.m_mass.col2.z = this.m_mass.col3.y;
		this.m_mass.col3.z = iA + iB;

		if (step.warmStarting) {
			// Scale impulses to support a variable time step.
			this.m_impulse.x *= step.dtRatio;
			this.m_impulse.y *= step.dtRatio;
			this.m_impulse.z *= step.dtRatio;

			bA.m_linearVelocity.x -= mA * this.m_impulse.x;
			bA.m_linearVelocity.y -= mA * this.m_impulse.y;
			bA.m_angularVelocity -= iA * (rAX * this.m_impulse.y - rAY * this.m_impulse.x + this.m_impulse.z);

			bB.m_linearVelocity.x += mB * this.m_impulse.x;
			bB.m_linearVelocity.y += mB * this.m_impulse.y;
			bB.m_angularVelocity += iB * (rBX * this.m_impulse.y - rBY * this.m_impulse.x + this.m_impulse.z);
		} else {
			this.m_impulse.SetZero();
		}

	}

	public SolveVelocityConstraints(step: b2TimeStep): void {
		//B2_NOT_USED(step);
		let tMat: b2Mat22;
		let tX: number;

		const bA: b2Body = this.m_bodyA;
		const bB: b2Body = this.m_bodyB;

		const vA: b2Vec2 = bA.m_linearVelocity;
		let wA: number = bA.m_angularVelocity;
		const vB: b2Vec2 = bB.m_linearVelocity;
		let wB: number = bB.m_angularVelocity;

		const mA: number = bA.m_invMass;
		const mB: number = bB.m_invMass;
		const iA: number = bA.m_invI;
		const iB: number = bB.m_invI;

		//b2Vec2 rA = b2Mul(bA->m_xf.R, m_localAnchorA - bA->GetLocalCenter());
		tMat = bA.m_xf.R;
		let rAX: number = this.m_localAnchorA.x - bA.m_sweep.localCenter.x;
		let rAY: number = this.m_localAnchorA.y - bA.m_sweep.localCenter.y;
		tX =  (tMat.col1.x * rAX + tMat.col2.x * rAY);
		rAY = (tMat.col1.y * rAX + tMat.col2.y * rAY);
		rAX = tX;
		//b2Vec2 rB = b2Mul(bB->m_xf.R, m_localAnchorB - bB->GetLocalCenter());
		tMat = bB.m_xf.R;
		let rBX: number = this.m_localAnchorB.x - bB.m_sweep.localCenter.x;
		let rBY: number = this.m_localAnchorB.y - bB.m_sweep.localCenter.y;
		tX =  (tMat.col1.x * rBX + tMat.col2.x * rBY);
		rBY = (tMat.col1.y * rBX + tMat.col2.y * rBY);
		rBX = tX;

		// Solve point-to-point constraint
		const Cdot1X: number = vB.x - wB * rBY - vA.x + wA * rAY;
		const Cdot1Y: number = vB.y + wB * rBX - vA.y - wA * rAX;
		const Cdot2: number = wB - wA;
		const impulse: b2Vec3 = new b2Vec3();
		this.m_mass.Solve33(impulse, -Cdot1X, -Cdot1Y, -Cdot2);

		this.m_impulse.Add(impulse);

		vA.x -= mA * impulse.x;
		vA.y -= mA * impulse.y;
		wA -= iA * (rAX * impulse.y - rAY * impulse.x + impulse.z);

		vB.x += mB * impulse.x;
		vB.y += mB * impulse.y;
		wB += iB * (rBX * impulse.y - rBY * impulse.x + impulse.z);

		// References has made some sets unnecessary
		//bA->this.m_linearVelocity = vA;
		bA.m_angularVelocity = wA;
		//bB->this.m_linearVelocity = vB;
		bB.m_angularVelocity = wB;

	}

	public SolvePositionConstraints(baumgarte: number): boolean {
		//B2_NOT_USED(baumgarte);
		let tMat: b2Mat22;
		let tX: number;

		const bA: b2Body = this.m_bodyA;
		const bB: b2Body = this.m_bodyB;

		// Compute the effective mass matrix.
		//b2Vec2 rA = b2Mul(bA->m_xf.R, m_localAnchorA - bA->GetLocalCenter());
		tMat = bA.m_xf.R;
		let rAX: number = this.m_localAnchorA.x - bA.m_sweep.localCenter.x;
		let rAY: number = this.m_localAnchorA.y - bA.m_sweep.localCenter.y;
		tX =  (tMat.col1.x * rAX + tMat.col2.x * rAY);
		rAY = (tMat.col1.y * rAX + tMat.col2.y * rAY);
		rAX = tX;
		//b2Vec2 rB = b2Mul(bB->m_xf.R, m_localAnchorB - bB->GetLocalCenter());
		tMat = bB.m_xf.R;
		let rBX: number = this.m_localAnchorB.x - bB.m_sweep.localCenter.x;
		let rBY: number = this.m_localAnchorB.y - bB.m_sweep.localCenter.y;
		tX =  (tMat.col1.x * rBX + tMat.col2.x * rBY);
		rBY = (tMat.col1.y * rBX + tMat.col2.y * rBY);
		rBX = tX;

		// J = [-I -r1_skew I r2_skew]
		//     [ 0       -1 0       1]
		// r_skew = [-ry; rx]

		// Matlab
		// K = [ mA+r1y^2*iA+mB+r2y^2*iB,  -r1y*iA*r1x-r2y*iB*r2x,          -r1y*iA-r2y*iB]
		//     [  -r1y*iA*r1x-r2y*iB*r2x, mA+r1x^2*iA+mB+r2x^2*iB,           r1x*iA+r2x*iB]
		//     [          -r1y*iA-r2y*iB,           r1x*iA+r2x*iB,                   iA+iB]

		const mA: number = bA.m_invMass;
		const mB: number = bB.m_invMass;
		let iA: number = bA.m_invI;
		let iB: number = bB.m_invI;

		//b2Vec2 C1 =  bB->this.m_sweep.c + rB - bA->this.m_sweep.c - rA;
		const C1X: number =  bB.m_sweep.c.x + rBX - bA.m_sweep.c.x - rAX;
		const C1Y: number =  bB.m_sweep.c.y + rBY - bA.m_sweep.c.y - rAY;
		const C2: number = bB.m_sweep.a - bA.m_sweep.a - this.m_referenceAngle;

		// Handle large detachment.
		const k_allowedStretch: number = 10.0 * b2Settings.b2_linearSlop;
		const positionError: number = Math.sqrt(C1X * C1X + C1Y * C1Y);
		const angularError: number = b2Math.Abs(C2);
		if (positionError > k_allowedStretch) {
			iA *= 1.0;
			iB *= 1.0;
		}

		this.m_mass.col1.x = mA + mB + rAY * rAY * iA + rBY * rBY * iB;
		this.m_mass.col2.x = -rAY * rAX * iA - rBY * rBX * iB;
		this.m_mass.col3.x = -rAY * iA - rBY * iB;
		this.m_mass.col1.y = this.m_mass.col2.x;
		this.m_mass.col2.y = mA + mB + rAX * rAX * iA + rBX * rBX * iB;
		this.m_mass.col3.y = rAX * iA + rBX * iB;
		this.m_mass.col1.z = this.m_mass.col3.x;
		this.m_mass.col2.z = this.m_mass.col3.y;
		this.m_mass.col3.z = iA + iB;

		const impulse: b2Vec3 = new b2Vec3();
		this.m_mass.Solve33(impulse, -C1X, -C1Y, -C2);

		bA.m_sweep.c.x -= mA * impulse.x;
		bA.m_sweep.c.y -= mA * impulse.y;
		bA.m_sweep.a -= iA * (rAX * impulse.y - rAY * impulse.x + impulse.z);

		bB.m_sweep.c.x += mB * impulse.x;
		bB.m_sweep.c.y += mB * impulse.y;
		bB.m_sweep.a += iB * (rBX * impulse.y - rBY * impulse.x + impulse.z);

		bA.SynchronizeTransform();
		bB.SynchronizeTransform();

		return positionError <= b2Settings.b2_linearSlop && angularError <= b2Settings.b2_angularSlop;

	}

	private m_localAnchorA: b2Vec2 = new b2Vec2();
	private m_localAnchorB: b2Vec2 = new b2Vec2();
	private m_referenceAngle: number;

	private m_impulse: b2Vec3 = new b2Vec3();
	private m_mass: b2Mat33 = new b2Mat33();
}