4230-hw-1/Pendulum/PendulumComponents.js

// PendulumComponents.js
// John Breaux  2022-06-30
// Classes used by Pendulum.js

"use strict";

//
// Classes
//

// Polygon class: Construct and display a regular polygon in 2D
class Polygon extends ShapedObject {
   // constructor: Make a new regular polygon
   constructor({ sides = 6, radius = 1, center = { x: 0, y: 0 }, color = { r: 0, g: 0, b: 1, a: 1 } } = {}) {
      super({ color: color });
      // Create vertices
      this.vertices = [];
      for (var i = 0; i <= sides; i++) {
         // Create vertices by adding center-point in Homogeneous coordinates to an offset vector generated from polar coordinates.
         this.vertices[i] = new Homogeneous2D().from_polar(radius, 2 * Math.PI * i / sides, 0).add_m(new Homogeneous2D(center.x, center.y, 1));
      }
   }
   // Wrap the init function to set the draw_primitive type to TRIANGLE_FAN
   init(gl) {
      this.draw_primitive = gl.TRIANGLE_FAN;
      super.init(gl);
   }
}

class Rod extends ShapedObject {
   constructor({ anchor = { x: 0, y: 0 }, bob = { x: 0, y: 0 }, color = { r: 1.0, g: 0.0, b: 0.0, a: 1.0 } } = {}) {
      super({ color: color });
      // Set the object's vertices
      this.vertices = [new Homogeneous2D(anchor.x, anchor.y, 1), new Homogeneous2D(bob.x, bob.y, 1)]
   }
   // Wrap the init function to set the draw_primitive type to LINES
   init(gl) {
      this.draw_primitive = gl.LINES;
      super.init(gl);
   }
}

class Anchor extends ShapedObject {
   constructor({ center = { x: 0, y: 0 }, color = { r: 0.0, g: 1.0, b: 0.0, a: 1.0 } } = {}) {
      super({ color: color });
      // Set the object's vertices
      this.vertices = [new Homogeneous2D(center.x, center.y, 1)];
   }
   // Wrap the init function to set the draw_primitive type to POINTS
   init(gl) {
      this.draw_primitive = gl.POINTS;
      super.init(gl);
   }
}

// This doesn't need to extend ShapedObject, but I love the symmetry
class Pendulum extends ShapedObject {
   constructor({ angle = 60, length = PEN_LENGTH, radius = BOB_RADIUS } = {}) {
      super();
      this.angle_initial = angle;
      this.angle = angle;
      this.period = Math.sqrt(9.81 / length);
      // define where anchor and bob are
      var anchor = { x: 0, y: 0 }, bob = { x: 0, y: -length };
      // create the components
      this.components = [
         new Rod({ anchor: anchor, bob: bob }),
         new Anchor({ center: anchor }),
         new Polygon({ sides: 6, radius: radius, center: bob })
      ];
   }

   // Initialize the pendulum
   init(gl) {
      // initialize the components
      for (var component of this.components) {
         component?.init(gl);
      }
      // start the clock
      this.t_prev = Date.now();
   }

   // Draw the pendulum
   draw(gl, modelMatrix, u_ModelMatrix) {
      // Rotate the pendulum
      modelMatrix.setIdentity();
      modelMatrix.rotate(this.angle, 0, 0, 1);
      // Draw each component
      for (var component of this.components) {
         component?.draw(gl, modelMatrix, u_ModelMatrix);
      }
   }

   // Tick the pendulum (update and perform movement)
   tick() {
      if (REAL_PENDULUM_MODE) {
         var now = Date.now(), elapsed = (now - this.t_prev) / 1000 * this.period;
         this.angle = this.angle_initial * Math.cos(elapsed);
      } else {
         var now = Date.now(), elapsed = now - this.t_prev;
         this.t_prev = now;
         this.angle = (this.angle + (A_VELOCITY * elapsed / 1000)) % 360;
      }
   }
}