createCanvas(400, 400);

    rectMode(CENTER);   // now the first two arguments of a rect are its center point, not corner

}

function draw(){

    background(240);

​

    // move the origin to the pivot point

    translate(150, 150); 

​

    // then rotate the grid around the pivot point by a

    // number of degrees equal to the frame count of the sketch

    rotate(radians(frameCount));

​

    // and draw the square at the origin

    fill(0);

    rect(0, 0, 100, 100);

}