Breakable.js

/*
 * Copyright (c) 2016-2018 Ali Shakiba http://shakiba.me/planck.js
 * Copyright (c) 2008-2009 Erin Catto  http://www.box2d.org
 *
 * This software is provided 'as-is', without any express or implied
 * warranty.  In no event will the authors be held liable for any damages
 * arising from the use of this software.
 * Permission is granted to anyone to use this software for any purpose,
 * including commercial applications, and to alter it and redistribute it
 * freely, subject to the following restrictions:
 * 1. The origin of this software must not be misrepresented; you must not
 * claim that you wrote the original software. If you use this software
 * in a product, an acknowledgment in the product documentation would be
 * appreciated but is not required.
 * 2. Altered source versions must be plainly marked as such, and must not be
 * misrepresented as being the original software.
 * 3. This notice may not be removed or altered from any source distribution.
 */

// This is used to test sensor shapes.
planck.testbed('Breakable', function(testbed) {
  var pl = planck, Vec2 = pl.Vec2;
  var world = new pl.World(Vec2(0, -10));

  var m_velocity;
  var m_angularVelocity;

  var m_broke = false;
  var m_break = false;

  var e_count = 7;

  // Ground body
  var ground = world.createBody();
  ground.createFixture(pl.Edge(Vec2(-40.0, 0.0), Vec2(40.0, 0.0)), 0.0);

  // Breakable dynamic body
  var m_body1 = world.createDynamicBody({
    position : Vec2(0.0, 40.0),
    angle : 0.25 * Math.PI
  });

  var m_shape1 = pl.Box(0.5, 0.5, Vec2(-0.5, 0.0), 0.0);
  var m_piece1 = m_body1.createFixture(m_shape1, 1.0);

  var m_shape2 = pl.Box(0.5, 0.5, Vec2(0.5, 0.0), 0.0);
  var m_piece2 = m_body1.createFixture(m_shape2, 1.0);

  world.on('post-solve', function (contact, impulse) {
    if (m_broke) {
      // The body already broke.
      return;
    }

    // Should the body break?
    var count = contact.getManifold().pointCount;

    var maxImpulse = 0.0;
    for (var i = 0; i < count; ++i) {
      maxImpulse = Math.max(maxImpulse, impulse.normalImpulses[i]);
    }

    if (maxImpulse > 40.0) {
      // Flag the body for breaking.
      m_break = true;
    }
  });

  function Break() {
    // Create two bodies from one.
    var body1 = m_piece1.getBody();
    var center = body1.getWorldCenter();

    body1.destroyFixture(m_piece2);
    m_piece2 = null;

    var body2 = world.createDynamicBody({
      type : 'dynamic',
      position : body1.getPosition(),
      angle : body1.getAngle()
    });

    m_piece2 = body2.createFixture(m_shape2, 1.0);

    // Compute consistent velocities for new bodies based on
    // cached velocity.
    var center1 = body1.getWorldCenter();
    var center2 = body2.getWorldCenter();

    var velocity1 = Vec2.add(m_velocity, Vec2.cross(m_angularVelocity, Vec2.sub(center1, center)));
    var velocity2 = Vec2.add(m_velocity, Vec2.cross(m_angularVelocity, Vec2.sub(center2, center)));

    console.log(velocity1, velocity2);

    body1.setAngularVelocity(m_angularVelocity);
    body1.setLinearVelocity(velocity1);

    body2.setAngularVelocity(m_angularVelocity);
    body2.setLinearVelocity(velocity2);
  }

  testbed.step = function() {
    if (m_break) {
      Break();
      m_broke = true;
      m_break = false;
    }

    // Cache velocities to improve movement on breakage.
    if (m_broke == false) {
      m_velocity = m_body1.getLinearVelocity();
      m_angularVelocity = m_body1.getAngularVelocity();
    }
  };

  return world;
});