a moving line, writen by Guru

void setup() {
    size(300,300);
    background( 0 );
    smooth();
    frameRate( 25 );
    strokeWeight( 3 );
}
int i = 0;
void draw() {
    fill( 0, 0, 0,  50 );
    noStroke();
    rect( 0, 0, width, height );
    int mx = width / 2;
    int my = height / 2;
    stroke( 255 );
    line( mx - 100 * cos( radians( i )), my - 100 * sin( radians( i )), 
          mx + 100 * cos( radians( i )), my - 10 * sin( radians( i ))); 

    i++;
    if ( i > 360 ) {
        i = 0;
    }
}