4230-hw-1/Pendulum/Pendulum.js

// RotatingTranslatedTriangle.js (c) 2012 matsuda

// Pendulum.js
// John Breaux  2022-06-30
// Simulates a pendulum in a frictionless vacuum with no gravity

"use strict"

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

  void main()
  {
    gl_Position = u_ModelMatrix * a_Position;
    gl_PointSize = 5.0;
  }	`;


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;

// Common functions:
//  acquire_buffer: Get a vertex buffer object from gl
function acquire_buffer(gl) {
  // Create a buffer object
  var vertexBuffer = gl.createBuffer();
  if (!vertexBuffer) {
    console.log('Failed to create the buffer object');
    return -1;
  }
  return vertexBuffer;
}

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 Pendulum({ angle: 0, length: PEN_LENGTH, radius: BOB_RADIUS });
  init(gl, pendulum);

  // 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;
  }

  // Model matrix
  var modelMatrix = new Matrix4();
  // Set it to the I matrix
  modelMatrix.setIdentity();

  // Start drawing
  var tick = function () {
    // Tick the pendulum
    pendulum.tick();
    // Draw the pendulum
    draw(gl, pendulum, modelMatrix, u_ModelMatrix);
    // Request that the browser ?calls tick
    requestAnimationFrame(tick, canvas);
  };
  tick();
}

function init(gl, pendulum) {
  pendulum.init(gl);
}

function draw(gl, pendulum, modelMatrix, u_ModelMatrix) {
  // Clear <canvas>
  gl.clear(gl.COLOR_BUFFER_BIT);
  // Draw the pendulum
  pendulum.draw(gl, modelMatrix, u_ModelMatrix);
}

function up() {
  A_VELOCITY += 10;
}

function down() {
  A_VELOCITY -= 10;
}