@awayfl/awayfl-player/lib/Box2D/Collision/Shapes/b2CircleShape.ts

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

import { b2Shape } from './b2Shape';
import { b2Transform, b2Vec2, b2Mat22, b2Math } from '../../Common/Math';
import { b2RayCastOutput } from '../b2RayCastOutput';
import { b2RayCastInput } from '../b2RayCastInput';
import { b2AABB } from '../b2AABB';
import { b2MassData } from './b2MassData';
import { b2Settings } from '../../Common/b2Settings';

/**
* A circle shape.
* @see b2CircleDef
*/
export class b2CircleShape extends b2Shape {
	__fast__: boolean = true;

	public Copy(): b2Shape {
		const s: b2Shape = new b2CircleShape();
		s.Set(this);
		return s;
	}

	public Set(other: b2Shape): void {
		super.Set(other);
		if (other instanceof b2CircleShape) {
			const other2: b2CircleShape = other as b2CircleShape;
			this.m_p.SetV(other2.m_p);
		}
	}

	/**
	* @inheritDoc
	*/
	public TestPoint(transform: b2Transform, p: b2Vec2): boolean {
		//b2Vec2 center = transform.position + b2Mul(transform.R, m_p);
		const tMat: b2Mat22 = transform.R;
		let dX: number = transform.position.x + (tMat.col1.x * this.m_p.x + tMat.col2.x * this.m_p.y);
		let dY: number = transform.position.y + (tMat.col1.y * this.m_p.x + tMat.col2.y * this.m_p.y);
		//b2Vec2 d = p - center;
		dX = p.x - dX;
		dY = p.y - dY;
		//return b2Dot(d, d) <= m_radius * m_radius;
		return (dX * dX + dY * dY) <= this.m_radius * this.m_radius;
	}

	/**
	* @inheritDoc
	*/
	public RayCast(output: b2RayCastOutput, input: b2RayCastInput, transform: b2Transform): boolean {
		//b2Vec2 position = transform.position + b2Mul(transform.R, m_p);
		const tMat: b2Mat22 = transform.R;
		const positionX: number = transform.position.x + (tMat.col1.x * this.m_p.x + tMat.col2.x * this.m_p.y);
		const positionY: number = transform.position.y + (tMat.col1.y * this.m_p.x + tMat.col2.y * this.m_p.y);

		//b2Vec2 s = input.p1 - position;
		const sX: number = input.p1.x - positionX;
		const sY: number = input.p1.y - positionY;
		//float32 b = b2Dot(s, s) - m_radius * m_radius;
		const b: number = (sX * sX + sY * sY) - this.m_radius * this.m_radius;

		/*// Does the segment start inside the circle?
		if (b < 0.0)
		{
			output.fraction = 0;
			output.hit = e_startsInsideCollide;
			return;
		}*/

		// Solve quadratic equation.
		//b2Vec2 r = input.p2 - input.p1;
		const rX: number = input.p2.x - input.p1.x;
		const rY: number = input.p2.y - input.p1.y;
		//float32 c =  b2Dot(s, r);
		const c: number =  (sX * rX + sY * rY);
		//float32 rr = b2Dot(r, r);
		const rr: number = (rX * rX + rY * rY);
		const sigma: number = c * c - rr * b;

		// Check for negative discriminant and short segment.
		if (sigma < 0.0 || rr < Number.MIN_VALUE) {
			return false;
		}

		// Find the point of intersection of the line with the circle.
		let a: number = -(c + Math.sqrt(sigma));

		// Is the intersection point on the segment?
		if (0.0 <= a && a <= input.maxFraction * rr) {
			a /= rr;
			output.fraction = a;
			// manual inline of: output.normal = s + a * r;
			output.normal.x = sX + a * rX;
			output.normal.y = sY + a * rY;
			output.normal.Normalize();
			return true;
		}

		return false;
	}

	/**
	* @inheritDoc
	*/
	public ComputeAABB(aabb: b2AABB, transform: b2Transform): void {
		//b2Vec2 p = transform.position + b2Mul(transform.R, m_p);
		const tMat: b2Mat22 = transform.R;
		const pX: number = transform.position.x + (tMat.col1.x * this.m_p.x + tMat.col2.x * this.m_p.y);
		const pY: number = transform.position.y + (tMat.col1.y * this.m_p.x + tMat.col2.y * this.m_p.y);
		aabb.lowerBound.Set(pX - this.m_radius, pY - this.m_radius);
		aabb.upperBound.Set(pX + this.m_radius, pY + this.m_radius);
	}

	/**
	* @inheritDoc
	*/
	public ComputeMass(massData: b2MassData, density: number): void {
		massData.mass = density * b2Settings.b2_pi * this.m_radius * this.m_radius;
		massData.center.SetV(this.m_p);

		// inertia about the local origin
		//massData.I = massData.mass * (0.5 * m_radius * m_radius + b2Dot(m_p, m_p));
		massData.I = massData.mass * (0.5 * this.m_radius * this.m_radius + (this.m_p.x * this.m_p.x + this.m_p.y * this.m_p.y));
	}

	/**
	* @inheritDoc
	*/
	public ComputeSubmergedArea(
		normal: b2Vec2,
		offset: number,
		xf: b2Transform,
		c: b2Vec2): number {
		const p: b2Vec2 = b2Math.MulX(xf, this.m_p);
		const l: number = -(b2Math.Dot(normal, p) - offset);

		if (l < -this.m_radius + Number.MIN_VALUE) {
			//Completely dry
			return 0;
		}
		if (l > this.m_radius) {
			//Completely wet
			c.SetV(p);
			return Math.PI * this.m_radius * this.m_radius;
		}

		//Magic
		const r2: number = this.m_radius * this.m_radius;
		const l2: number = l * l;
		const area: number = r2 * (Math.asin(l / this.m_radius) + Math.PI / 2) + l * Math.sqrt(r2 - l2);
		const com: number = -2 / 3 * Math.pow(r2 - l2, 1.5) / area;

		c.x = p.x + normal.x * com;
		c.y = p.y + normal.y * com;

		return area;
	}

	/**
	 * Get the local position of this circle in its parent body.
	 */
	public GetLocalPosition(): b2Vec2 {
		return this.m_p;
	}

	/**
	 * Set the local position of this circle in its parent body.
	 */
	public SetLocalPosition(position: b2Vec2): void {
		this.m_p.SetV(position);
	}

	/**
	 * Get the radius of the circle
	 */
	public GetRadius(): number {
		return this.m_radius;
	}

	/**
	 * Set the radius of the circle
	 */
	public SetRadius(radius: number): void {
		this.m_radius = radius;
	}

	constructor(radius: number = 0) {
		super();
		this.m_type = b2Shape.e_circleShape;
		this.m_radius = radius;
	}

	// Local position in parent body
	public m_p: b2Vec2 = new b2Vec2();

}