// HelloPoint2.js (c) 2012 matsuda, 2022 Jonathon Doran
"use strict";

// Vertex shader program
const vertex_shader = `
	attribute vec4 a_Position;    // attribute variables are assigned by the main program

	void main()
	{
		gl_Position = a_Position;
		gl_PointSize = 1.0;
	}	`;

// Fragment shader program
const fragment_shader = `
	void main()
	{
		gl_FragColor = vec4(0.2, 0.8, 1.0, 1.0);  // Set the point color to a nice cyan
	}	`;

//
// Chaos Game
//

// Classes
//   vec2: 2D vectors
class vec2 {
  constructor(x = 0, y = 0) {
    this.x = x;
    this.y = y;
  }
  add(rhs) {
    if (rhs)
      return new vec2(this.x + rhs.x, this.y + rhs.y);
    return null;
  }
  sub(rhs) {
    if (rhs)
      return new vec2(this.x - rhs.x, this.y - rhs.y);
    return null;
  }
  copy() {
    return new vec2(this.x, this.y);
  }
  move_halfway(rhs) {
    // Calculate the vector direction to move in, and change in that direction.
    this.x += (rhs.x - this.x) / 2;
    this.y += (rhs.y - this.y) / 2;
  }
}

// triangle2 class: Holds 3 vertices, represented as vectors from the origin
class triangle2 {
  // constructor: Make a new triangle
  constructor({ v0 = null, v1 = null, v2 = null, type = "scalene", radius = 0, center = {x: 0, y: 0}} = {}) {
    this.v = [, ,]
    this.v[0] = v0;
    this.v[1] = v1;
    this.v[2] = v2;
    if (type === "equilateral") {
      this.make_equilateral(radius, center);
    }
  }
  // make_equilateral: construct an equilateral triangle
  // @param radius: Distance from center of triangle to vertices
  make_equilateral(radius, center = {x: 0, y: 0}) {
    // compute the math constants
    const r_sin_120 = Math.sin(Math.PI / 3) * radius;
    const r_cos_120 = 0.5 * radius;

    // Equilateral triangle centered on origin
    this.v[0] = new vec2(-r_sin_120, -r_cos_120).add(center);
    this.v[1] = new vec2(0, radius).add(center);
    this.v[2] = new vec2(r_sin_120, -r_cos_120).add(center);
  }
  get_vertex(index) { return this.v[index]; }
  get_rand_vertex() { return this.v[Math.floor(Math.random() * 3)]; }
}

// function draw_point: draw a point
function draw_point(gl, a_Position, p) {
  // Pass vertex position to attribute variable
  gl.vertexAttrib3f(a_Position, p.x, p.y, 0.0);
  // Draw
  gl.drawArrays(gl.POINTS, 0, 1);
}

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;
  }

  // Get the storage location of a_Position
  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;
  }

  // Specify the color for clearing canvas as black, and clear canvas
  gl.clearColor(0.0, 0.0, 0.0, 1.0);
  gl.clear(gl.COLOR_BUFFER_BIT);

  // make an equilateral triangle of radius 0.8
  var triangle = new triangle2({type: "equilateral", radius: 0.8});
  // initialize point p to a copy of one of the vectors
  var i, p = triangle.get_vertex(0)?.copy();
  // loop for ten thousand years
  for (i = 0; i < 50000; i++) {
    // get a random vertex
    var random_vertex = triangle.get_rand_vertex();
    // move to the midpoint
    p.move_halfway(random_vertex);
    // draw point
    draw_point(gl, a_Position, p);
  }
}