4230-hw-1/Pendulum/Pendulum.js

// RotatingTranslatedTriangle.js (c) 2012 matsuda
"use strict"

const vertex_shader = `
  attribute vec4 a_Position;
  uniform mat4 u_ModelMatrix;

  void main()
  {
    gl_Position = u_ModelMatrix * a_Position;
  }	`;


const fragment_shader = `
  void main()
  {
    gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);
  }	`;

// Point size of the anchor
var POINT_SIZE = 5;
// Radius of the bob
var BOB_RADIUS = 0.1;
// length of the wire
var PEN_LENGTH = 0.8;
// Rotation angle (degrees/second)
var A_VELOCITY = 45.0;

// Classes
//   homo2: Stores a 2d vector or point in homog. coords
class homog2 {
  constructor(x = 0, y = 0, w = 0) {
    this.x = x;
    this.y = y;
    this.w = w;
  }
  // Add with modify
  add_m(rhs) {
    if (rhs) {
      this.x += rhs.x;
      this.y += rhs.y;
      this.w += rhs.w;
      return this;
    }
    else return null;
  }
  // scalar multiply with modify
  smul_m(scalar) {
    if (typeof(rhs) === "number") {
      this.x *= rhs;
      this.y *= rhs;
      this.w *= rhs;
      return this;
    }
    else return null;
  }
  // copy
  copy() {
    return new homog2(this.x, this.y, this.w);
  }
  // create vector/point from 2d polar coordinates
  from_polar(r = 0, theta = 0, w = 0) {
    this.x = r * Math.cos(theta);
    this.y = r * Math.sin(theta);
    this.w = w;
    return this;
  }
}

// hexagon2 class: Holds 6 vertices and a center point. Only constructs perfect hexagons.
class hexagon2 {
  // constructor: Make a new regular polygon
  constructor({sides = 6, radius = 0, rotation = 0, center = { x: 0, y: 0 } } = {}) {
    // lenth is center + sides
    this.length = 1;
    this.center = new homog2(center.x, center.y, 1);
    this.v = [];
    for (var i = 0; i <= sides; i++) {
      this.v[i] = new homog2().from_polar(radius, rotation + (i*2*Math.PI / sides)).add_m(this.center);
      this.length++;
    }
  }
  // Convert to Float32Array [center, v0, v1, ...]
  to_array() {
    // allocate space for center.xy + vertices.xy
    var ret = new Float32Array((1 + this.v.length) * 2);
    // save the center
    ret[0] = this.center.x;
    ret[1] = this.center.y;
    // save the vertices
    for (var i = 0; i < this.v.length; i++) {
      var j = 2 * (i + 1);
      ret[j]   = this.v[i].x;
      ret[j+1] = this.v[i].y;
    }
    return ret;
  }
  draw(gl, n, currentAngle, modelMatrix, u_ModelMatrix) {
    // Set the rotation matrix
    modelMatrix.setRotate(currentAngle, 0, 0, 1);
    // Pass the rotation matrix to the vertex shader
    gl.uniformMatrix4fv(u_ModelMatrix, false, modelMatrix.elements);
    // Clear <canvas>
    gl.clear(gl.COLOR_BUFFER_BIT);
    // Draw the pendulum
    gl.drawArrays(gl.TRIANGLE_FAN, 0, n);
  }
}

class pendulum2 {
  constructor({angle = 0, length = PEN_LENGTH, radius = BOB_RADIUS} = {}) {
    this.bob = new hexagon2({radius: radius, center: {x: 0, y: -length}});
    console.log(this);
  }
}

function main() {
  // Retrieve <canvas> element
  var canvas = document.getElementById('webgl');

  // Get the rendering context for WebGL
  var gl = getWebGLContext(canvas);
  if (!gl) {
    console.log('Failed to get the rendering context for WebGL');
    return;
  }

  // Initialize shaders
  if (!initShaders(gl, vertex_shader, fragment_shader)) {
    console.log('Failed to intialize shaders.');
    return;
  }

  // create a pendulum object
  var pendulum = new pendulum2({angle: 0, length: 0});

  // Write the positions of vertices to a vertex shader
  var n = initVertexBuffers(gl, pendulum);
  if (n < 0) {
    console.log('Failed to set the positions of the vertices');
    return;
  }

  // Specify the color for clearing <canvas>
  gl.clearColor(0, 0, 0, 1);

  // Get storage location of u_ModelMatrix
  var u_ModelMatrix = gl.getUniformLocation(gl.program, 'u_ModelMatrix');
  if (!u_ModelMatrix) {
    console.log('Failed to get the storage location of u_ModelMatrix');
    return;
  }

  // Current rotation angle
  var currentAngle = 0.0;

  // Model matrix
  var modelMatrix = new Matrix4();

  // Start drawing
  var tick = function () {
    currentAngle = animate(currentAngle);  // Update the rotation angle
    pendulum.bob.draw(gl, n, currentAngle, modelMatrix, u_ModelMatrix);   // Draw the triangle
    requestAnimationFrame(tick, canvas);   // Request that the browser ?calls tick
  };
  tick();
}

function initVertexBuffers(gl, pendulum) {
  // var vertices = new Float32Array([
  //   0, 0.5, -0.5, -0.5, 0.5, -0.5
  // ]);
  // var n = 3;   // The number of vertices
  var vertices = pendulum.bob.to_array();
  var n = pendulum.bob.length;

  // Create a buffer object
  var vertexBuffer = gl.createBuffer();
  if (!vertexBuffer) {
    console.log('Failed to create the buffer object');
    return -1;
  }

  // Bind the buffer object to target
  gl.bindBuffer(gl.ARRAY_BUFFER, vertexBuffer);

  // Write date into the buffer object
  gl.bufferData(gl.ARRAY_BUFFER, vertices, gl.STATIC_DRAW);

  // Assign the buffer object to a_Position variable
  var a_Position = gl.getAttribLocation(gl.program, 'a_Position');
  if (a_Position < 0) {
    console.log('Failed to get the storage location of a_Position');
    return -1;
  }
  gl.vertexAttribPointer(a_Position, 2, gl.FLOAT, false, 0, 0);

  // Enable the assignment to a_Position variable
  gl.enableVertexAttribArray(a_Position);

  return n;
}

function draw(gl, n, currentAngle, modelMatrix, u_ModelMatrix) {
  // Set the rotation matrix
  modelMatrix.setRotate(currentAngle, 0, 0, 1);
  modelMatrix.translate(0.35, 0, 0);

  // Pass the rotation matrix to the vertex shader
  gl.uniformMatrix4fv(u_ModelMatrix, false, modelMatrix.elements);

  // Clear <canvas>
  gl.clear(gl.COLOR_BUFFER_BIT);

  // Draw the rectangle
  gl.drawArrays(gl.TRIANGLES, 0, n);
}

// Last time that this function was called
var g_last = Date.now();
function animate(angle) {
  // Calculate the elapsed time
  var now = Date.now();
  var elapsed = now - g_last;
  g_last = now;
  // Update the current rotation angle (adjusted by the elapsed time)
  var newAngle = angle + (A_VELOCITY * elapsed) / 1000.0;
  return newAngle %= 360;
}

function up() {
  A_VELOCITY += 10;
}

function down() {
  A_VELOCITY -= 10;
}