rl_2d_walker.js/js/floor.js

function createFloor() {
  var body_def = new b2.BodyDef();
  var body = globals.world.CreateBody(body_def);
  var fix_def = new b2.FixtureDef();
  fix_def.friction = 0.8;
  fix_def.shape = new b2.ChainShape();

  // start with flat floor
  var edges = [
    new b2.Vec2(-3.5, 4), // back wall
    new b2.Vec2(-3.5, -0.16),
    new b2.Vec2(2.5, -0.16)
  ];

  for(var k = 2; k < config.max_floor_tiles; k++) {
    var ratio = k / config.max_floor_tiles;
    // add uneven floor by continuing from the last point, plus some random jittering
    edges.push(new b2.Vec2(
      edges[edges.length - 1].x + (1 + ratio * Math.random() - ratio / 2),
      edges[edges.length - 1].y + (ratio * Math.random() - ratio / 2)* 2));
//    edges.push(new b2.Vec2(edges[edges.length-1].x + 1,-0.16));
  }
  edges.push(new b2.Vec2(edges[edges.length-1].x, edges[edges.length-1].y + 8)); // front wall
  fix_def.shape.CreateChain(edges, edges.length);
  body.CreateFixture(fix_def);
  return body;
}