const screen_height = 1024;

let drawing = true;

let timestep = 0;

let lastY = 0;

let s_count = 0; //time to sustain;

let s = 0.75;

let r = 0.0025;

let stage = 0;

let y = 0.0;

let expo;

let releaseStartY = s;

​

function setup() {

  console.log('start'); 

  createCanvas(screen_width, screen_height);

  background(220);

}

​

function expoCalc(startTC, endTC, t) {

  const maxY = (1-Math.pow(Math.E, (-endTC))); //scaling factor

  if (endTC > startTC) return (1-Math.pow(Math.E, (t*-endTC)))/maxY;

  return (Math.pow(Math.E, (t*-startTC)));

}

​

function mousePressed() {

  if (!drawing) background(220);

  drawing = true;

  stage = 0;

  //reset position. translate current pos to % of attack

  const maxY = (1-Math.pow(Math.E, (-2.5))); //scaling factor

  y = Math.log(Math.abs((expo*maxY)-1))/-2.5;///(-0.435);

  console.log({maxY, expo, y});

  expo = y;

}

​

function draw() {

  if (!drawing) return;  

  //let a = exp(mouseX /screen_width)/200 -.005;

  let a = 0.01;

  //if (mouseX <= 0) a =.01;

  //let d = 0.01;

  let d = exp(mouseX /screen_width)/200 -.005;

  if (mouseX <= 0) d =.01;

​

  for (i = timestep; i < (timestep + 4); i++) {

    expo = y;

    if (!mouseIsPressed) {

        releaseStartY = y;

        stage = 3;

      }

    if(stage == 0) { //atack

      y += a;

      if (y >= 1) {

        stage = 1;

        y = 1;

      }

      expo = expoCalc(0, 2.5, y);

    } else if (stage == 1) { //decay

      y -= d;      

      expo = (expoCalc(10, 0, 1-y) * (1-s)) + s;

      //expo = y;

      if (expo - s < 0.0002) stage = 2;

    } else if (stage == 2) { //sustain

      y = s;

      expo = s;

      //if (s_count++ >= 1) stage = 3;

​

    } else if (stage == 3) { //release

      y -= r;

      if (y < 0.0001) stage = 4;

      expo = expoCalc(10, 0, 1-y/releaseStartY)*releaseStartY;

    }

    stroke(0);

    line (i-1, (1-lastY)*screen_height, i, (1-expo)*screen_height);

    lastY = expo;

    stroke(255,0,0);

    point(i, (1-y)*screen_height);

  }

  timestep = i;

  stroke(255,0,0);

​

  if (timestep >= screen_width) {

    timestep = 0;

    drawing = false;

    expo = 0;

  }

}