oh-my-geometry

Cheatsheet for frequently used procedural 2D geometry in p5

Get the length of a line segment

Subtract two position vectors to get a direction vector between them.

function segLength(v1, v2) {
  return v2.copy().sub(v1.copy()).mag();
}

Get the angle between two vectors

The dot product divided by the magnitude product is the cosine of the angle.

function getAngle(v1, v2) {
  const dotProduct = v2.dot(v1);
  const magProduct = v1.mag() * v2.mag();
  return acos(dotProduct / magProduct);
}

Get the angles of all points in a triangle

function getAngles(points) {
  const ab = points[1].copy().sub(points[0].copy());
  const ac = points[2].copy().sub(points[0].copy());
  const angle1 = getAngle(ab, ac);
  
  const bc = points[2].copy().sub(points[1].copy());
  const ba = points[0].copy().sub(points[1].copy());
  const angle2 = getAngle(bc, ba);

  const ca = points[0].copy().sub(points[2].copy());
  const cb = points[1].copy().sub(points[2].copy());
  const angle3 = getAngle(ca, cb);
  return [angle1, angle2, angle3];
}

Get the midpoint of a line segment, the complicated way

function midpoint(x1, y1, x2, y2) {
  let v1 = createVector(x1, y1);
  let v2 = createVector(x2, y2);
  let direction = v2.sub(v1);
  let magnitude = direction.mag();
  direction.normalize();
  direction.mult(magnitude * 0.5);
  const x = x1 + direction.x;
  const y = y1 + direction.y;
  return createVector(x, y);
}

Get a point on a line segement and pass the length of the offset

function segpoint(x1, y1, x2, y2, len) {
  let v1 = createVector(x1, y1);
  let v2 = createVector(x2, y2);
  let direction = v2.sub(v1);
  let magnitude = direction.mag();
  direction.normalize();
  direction.mult(len);
  const x = x1 + direction.x;
  const y = y1 + direction.y;
  return createVector(x, y);
}