javascript find fixed degrees from radians

Question

I am trying to find fixed degrees of rotation of an image in a html page. The following code from the original author works perfectly for rotating the image.

I like to get the degrees of rotation from the initial starting point (which is 0), preferably limited to 0-360, whenever the image is rotated (multiple times).

HTML

Javascript code

const rotate = (EL) => {

  let ang = 0;
  let angStart = 0;
  let isStart = false;

  const angXY = (ev) => {
    const bcr = EL.getBoundingClientRect();
    const radius = bcr.width / 2;
    const { clientX, clientY } = ev.touches ? ev.touches[0] : ev;
    const y = clientY - bcr.top - radius;  // y from center
    const x = clientX - bcr.left - radius; // x from center
    return Math.atan2(y, x);
  };

  const mousedown = (ev) => {
    isStart = true;
    angStart = angXY(ev) - ang;
  };

  const mousemove = (ev) => {
    if (!isStart) return;
    ev.preventDefault();
    ang = angXY(ev) - angStart;
    EL.style.transform = `rotateZ(${ang}rad)`;
  };

  const mouseup = () => {
    console.log('mouse up to ', ang, ', ', getDegrees(ang));
    isStart = false;
  };

  EL.addEventListener("mousedown", mousedown);
  document.addEventListener("mousemove", mousemove);
  document.addEventListener("mouseup", mouseup);
};

function getDegrees(ang) {
  /* let deg = (ang * (180 / Math.PI) * -1) + 90;

  while (deg > 360) {
    deg -= 360;
  }

  while (deg < -360) {
    deg += 360;
  }

  return deg; */

  return ang * (180.0 / 3.141592653589793238463)
}

document.querySelectorAll(".rotate").forEach(rotate);

user_3807365 · Answer

Just remember the last angle. Then mod by 360 (and make it a positive)

var last_ang = null;

const rotate = (EL) => {

  let ang = 0;
  let angStart = 0;
  let isStart = false;

  const angXY = (ev) => {
    const bcr = EL.getBoundingClientRect();
    const radius = bcr.width / 2;
    const {
      clientX,
      clientY
    } = ev.touches ? ev.touches[0] : ev;
    const y = clientY - bcr.top - radius; // y from center
    const x = clientX - bcr.left - radius; // x from center
    return Math.atan2(y, x);
  };

  const mousedown = (ev) => {
    isStart = true;
    angStart = angXY(ev) - ang;
  };

  const mousemove = (ev) => {
    if (!isStart) return;
    ev.preventDefault();
    last_ang = ang;
    ang = angXY(ev) - angStart;
    EL.style.transform = `rotateZ(${ang}rad)`;
  };

  const mouseup = () => {
    console.log(getDegrees(ang) + " degrees");
    isStart = false;
  };

  EL.addEventListener("mousedown", mousedown);
  document.addEventListener("mousemove", mousemove);
  document.addEventListener("mouseup", mouseup);
};


function getDegrees(ang) {
  if (last_ang) {
    return (((last_ang * 180 / Math.PI) % 360 + 360) % 360).toFixed(2)

  }
  return 0

}

document.querySelectorAll(".rotate").forEach(rotate);

body {
  padding: 10px 50px;
}


  Drag and rotate

javascript find fixed degrees from radians

1 Answers