const regl = require('regl')();
const d3Random = require('d3-random');
const d3Array = require('d3-array');

const rng = d3Random.randomNormal(0, 0.1);
const { range } = d3Array;

const numPoints = 100000;

// the size of the points we draw on screen
const pointWidth = 2;

// dimensions of the viewport we are drawing in
const width = window.innerWidth;
const height = window.innerHeight;

// generaate some random points
const points = range(numPoints).map(i => ({
  x1: (rng() * width) + (width / 2),
  y1: (rng() * height) + (height / 2),
  x: rng(),
  y: rng(),
  size: Math.random() * 5 + pointWidth,
  color: [0, Math.random(), 0],
  delta: [rng(), rng()],
}));

// draw points
const drawStuff = regl({
  frag: `
    precision  mediump float;
    varying vec3 fragColor;


    void main() {
      float r = 0.0;
      float delta = 0.0;
      float alpha = 1.0;
      vec2 cxy = 2.0 * gl_PointCoord - 1.0;
      r = dot(cxy, cxy);
      if (r > 1.0) {
          discard;
      }

      gl_FragColor = vec4(fragColor, 0.5) * alpha;
    }
  `,
  vert: `
    precision  mediump float;
    attribute vec2 position;
    attribute vec2 delta;
    attribute vec3 color;
    attribute float size;


    varying vec3 fragColor;

    uniform float pointWidth;
    uniform float stageWidth;
    uniform float stageHeight;
    uniform float time;

    void main() {
      gl_PointSize = size;

      fragColor = color;
      gl_Position = vec4(position.x + sin(time * delta.x), position.y + cos(time * delta.y), 0.0, 1.0);
    }
  `,
  attributes: {
    position: points.map(d => [d.x, d.y]),
    delta: points.map(d => d.delta),
    color: points.map(d => [1.0,1.0,0.0]),
    size: points.map(d => d.size),
  },
  uniforms: {
    pointWidth: regl.prop('pointWidth'),
    stageWidth: regl.prop('width'),
    stageHeight: regl.prop('height'),
    time: regl.context('time'),
  },
  blend: {
  	enable: true,
    func: {
      srcRGB: 'src alpha',
      srcAlpha: 'src alpha',
      dstRGB: 'one minus src alpha',
      dstAlpha: 'one minus src alpha',
    },
  },
  depth: { enable: false },
  count: points.length,
  primitive: 'points',
})

// loop
regl.frame(({time}) => {
  regl.clear({
    color: [0,0,0,1],
    depth: 1,
  });
  drawStuff({
    pointWidth: pointWidth,
    width,
    height,
  });
})