planck-js/example/Cantilever.js

2D JavaScript physics engine for cross-platform HTML5 game development

/*
 * MIT License
 * Copyright (c) 2019 Erin Catto
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

// It is difficult to make a cantilever made of links completely rigid with weld joints.
// You will have to use a high number of iterations to make them stiff.
// So why not go ahead and use soft weld joints? They behave like a revolute
// joint with a rotational spring.
planck.testbed('Cantilever', function(testbed) {
  var pl = planck, Vec2 = pl.Vec2;
  var world = new pl.World(Vec2(0, -10));

  var COUNT = 8;

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

  var prevBody = ground;
  for (var i = 0; i < COUNT; ++i) {
    var body = world.createDynamicBody(Vec2(-14.5 + 1.0 * i, 5.0));
    body.createFixture(pl.Box(0.5, 0.125), 20.0);

    var anchor = Vec2(-15.0 + 1.0 * i, 5.0);
    world.createJoint(pl.WeldJoint({}, prevBody, body, anchor));

    prevBody = body;
  }

  var prevBody = ground;
  for (var i = 0; i < 3; ++i) {
    var body = world.createDynamicBody(Vec2(-14.0 + 2.0 * i, 15.0));
    body.createFixture(pl.Box(1.0, 0.125), 20.0);

    var anchor = Vec2(-15.0 + 2.0 * i, 15.0);
    world.createJoint(pl.WeldJoint({
      frequencyHz: 5.0,
      dampingRatio: 0.7,
    }, prevBody, body, anchor));

    prevBody = body;
  }

  var prevBody = ground;
  for (var i = 0; i < COUNT; ++i) {
    var body = world.createDynamicBody(Vec2(-4.5 + 1.0 * i, 5.0));
    body.createFixture(pl.Box(0.5, 0.125), 20.0);

    if (i > 0) {
      var anchor = Vec2(-5.0 + 1.0 * i, 5.0);
      world.createJoint(pl.WeldJoint({}, prevBody, body, anchor));
    }

    prevBody = body;
  }

  var prevBody = ground;
  for (var i = 0; i < COUNT; ++i) {
    var body = world.createDynamicBody(Vec2(5.5 + 1.0 * i, 10.0));
    body.createFixture(pl.Box(0.5, 0.125), 20.0);

    if (i > 0) {
      var anchor = Vec2(5.0 + 1.0 * i, 10.0);
      world.createJoint(pl.WeldJoint({
        frequencyHz: 8.0,
        dampingRatio: 0.7,
      }, prevBody, body, anchor));
    }

    prevBody = body;
  }

  for (var i = 0; i < 2; ++i) {
    var vertices = [];
    vertices[0] = Vec2(-0.5, 0.0);
    vertices[1] = Vec2(0.5, 0.0);
    vertices[2] = Vec2(0.0, 1.5);

    var body = world.createDynamicBody(Vec2(-8.0 + 8.0 * i, 12.0));
    body.createFixture(pl.Polygon(vertices), 1.0);
  }

  for (var i = 0; i < 2; ++i) {
    var body = world.createDynamicBody(Vec2(-6.0 + 6.0 * i, 10.0));
    body.createFixture(pl.Circle(0.5), 1.0);
  }

  return world;
});