// 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 = `
   precision mediump float;
   uniform vec4 u_Color;
   void main()
   {
      gl_FragColor = u_Color;
   }
`;

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({ length: PEN_LENGTH, radius: BOB_RADIUS });
   pendulum.init(gl);

   // 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 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;
}

function real() {
   REAL_PENDULUM_MODE = ! REAL_PENDULUM_MODE;
}