com.almasb.fxgl.physics.box2d.collision.Manifold Maven / Gradle / Ivy

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/*
 * FXGL - JavaFX Game Library. The MIT License (MIT).
 * Copyright (c) AlmasB ([email protected]).
 * See LICENSE for details.
 */
package com.almasb.fxgl.physics.box2d.collision;

import com.almasb.fxgl.core.math.Vec2;
import com.almasb.fxgl.physics.box2d.common.JBoxSettings;

/**
 * A manifold for two touching convex shapes. Box2D supports multiple types of contact:
 * 
 * clip point versus plane with radius
 * point versus point with radius (circles)
 * 
 * The local point usage depends on the manifold type:
 * 
 * e_circles: the local center of circleA
 * e_faceA: the center of faceA
 * e_faceB: the center of faceB
 * 
 * Similarly the local normal usage:
 * 
 * e_circles: not used
 * e_faceA: the normal on polygonA
 * e_faceB: the normal on polygonB
 * 
 * We store contacts in this way so that position correction can account for movement, which is
 * critical for continuous physics. All contact scenarios must be expressed in one of these types.
 * This structure is stored across time steps, so we keep it small.
 */
public class Manifold {

    public enum ManifoldType {
        CIRCLES, FACE_A, FACE_B
    }

    /** The points of contact. */
    public final ManifoldPoint[] points = new ManifoldPoint[JBoxSettings.maxManifoldPoints];

    /** not use for Type::e_points */
    public final Vec2 localNormal = new Vec2();

    /** usage depends on manifold type */
    public final Vec2 localPoint = new Vec2();

    public ManifoldType type;

    /** The number of manifold points. */
    public int pointCount = 0;

    /**
     * creates a manifold with 0 points, with it's points array full of instantiated ManifoldPoints.
     */
    public Manifold() {
        for (int i = 0; i < JBoxSettings.maxManifoldPoints; i++) {
            points[i] = new ManifoldPoint();
        }
    }

    /**
     * copies this manifold from the given one
     *
     * @param cp manifold to copy from
     */
    public void set(Manifold cp) {
        for (int i = 0; i < cp.pointCount; i++) {
            points[i].set(cp.points[i]);
        }

        type = cp.type;
        localNormal.set(cp.localNormal);
        localPoint.set(cp.localPoint);
        pointCount = cp.pointCount;
    }
}