phaser/src/physics/arcade/GetOverlapY.js

/**
 * @author       Richard Davey <rich@photonstorm.com>
 * @copyright    2019 Photon Storm Ltd.
 * @license      {@link https://github.com/photonstorm/phaser/blob/master/license.txt|MIT License}
 */

var IntersectsRect = require('./IntersectsRect');

/**
 * Calculates and returns the vertical overlap between two arcade physics bodies.
 * 
 * We know the bodies are intersecting based on a previous check, so the point of this function
 * is to determine which face the overlap is occurring on and at what depth.
 *
 * @function Phaser.Physics.Arcade.GetOverlapY
 * @since 3.0.0
 *
 * @param {Phaser.Physics.Arcade.Body} body1 - The first Body to separate.
 * @param {Phaser.Physics.Arcade.Body} body2 - The second Body to separate.
 * @param {boolean} [overlapOnly] - Is this an overlap only check, or part of separation?
 * @param {number} [bias] - A value added to the delta values during collision checks. Increase it to prevent sprite tunneling (sprites passing through each other instead of colliding).
 *
 * @return {number[]} An array containing the amount of overlap in element 0 and the face of body1 in element 1 (true = bottom, false = top).
 */
var GetOverlapY = function (body1, body2, overlapOnly, bias)
{
    if (overlapOnly === undefined) { overlapOnly = false; }
    if (bias === undefined) { bias = 0; }

    var overlap = 0;

    // var maxOverlap = body1.deltaAbsY() + body2.deltaAbsY() + bias;

    var distance1 = body1.bottom - body2.y;
    var distance2 = body2.bottom - body1.y;

    var prevDistance1 = (body1.prev.y + body1.height) - body2.prev.y;
    var prevDistance2 = (body2.prev.y + body2.height) - body1.prev.y;

    var embedded = false;

    var topFace = (distance1 > distance2 && prevDistance1 > prevDistance2);

    var intersects = IntersectsRect(body1, body2);

    if (!topFace)
    {
        //  body1 bottom is touching body2 top
        if (intersects)
        {
            overlap = distance1;
        }

        if (!body1.checkCollision.down || !body2.checkCollision.up)
        {
            overlap = 0;
            intersects = false;
        }

        if (!overlapOnly)
        {
            body1.setTouchingDown();
            body2.setTouchingUp();

            body1.setBlockedDown(body2, intersects);
            body2.setBlockedUp(body1, intersects);
        }
    }
    else
    {
        //  body1 top is touching body2 bottom
        if (intersects)
        {
            overlap = distance2;
        }

        if (!body1.checkCollision.up || !body2.checkCollision.down)
        {
            overlap = 0;
            intersects = false;
        }

        if (!overlapOnly)
        {
            body1.setTouchingUp();
            body2.setTouchingDown();

            body1.setBlockedUp(body2, intersects);
            body2.setBlockedDown(body1, intersects);
        }
    }

    //  Resets the overlapY to zero if there is no overlap, or to the actual pixel value if there is
    body1.overlapY = overlap;
    body2.overlapY = overlap;

    if (embedded)
    {
        //  We let the block resolution move it
        overlap = 0;

        body1.embedded = embedded;
        body2.embedded = embedded;
    }

    return { overlap: overlap, topFace: topFace, intersects: intersects };
};

module.exports = GetOverlapY;