function setup() {

  createCanvas(400, 400);

}

​

function draw() {

  background(220);

  //this is only in here to demonstrate that fill doesn't work on my rotated ellipse

  fill(255, 0, 0);

  circle(100, 100, 50);

  //rotatedEllipse(xCenter, yCenter, width, height, rotationAngle);

  rotatedEllipse(100, 200, 100, 200, angle);

  angle+=0.01;

}

​

function rotatedEllipse(x, y, xSize, ySize, alpha){

  for(let i = 0; i < 6.28; i+=0.01){

    //parametric coordinates of the "unrotated" ellipse

    //if alpha is set to 0, it will act just like the regular ellipse() function

    x1 = x + 0.5*xSize*cos(i);

    y1 = y + 0.5*ySize*sin(i);

    //this draws a series of points along the edge of the rotated ellipse

    //x and y are the center of the ellipse, which is also the center of rotation (rather than the origin)

    //x1 and y1 are the coordinates of the points of the ellipse before rotation

    //alpha is the angle of rotation

    point(x + (x1-x)*cos(alpha) - (y1 - y)*sin(alpha), y + (y1 - y)*cos(alpha) + (x1 - x)*sin(alpha));

  }

}