// circular motion prototyping

float sx,sy;
float mx,my;
int state;
float dark;

void setup() {
  size( 640,480);
  sx = -50;
  mx = -50;
  state = 0;
  dark = 110;
}

void draw(){
  background( 100,150,200 );
  fill( 100,200,100 );
  rect( -2,height/4, width+4,height*3/4 ); 
 // dark = constrain(0, 0, 150);
  noStroke();          
  fill(0,dark);
  rect(0,0,width,height); 
  if (state == 0){
    drawSun();
  }
  if (state == 1){
    drawMoon();
  }
  text(dark,40,height-40);
 
}
void drawSun(){
  sy = -sqrt(pow(1000,2)-pow(sx-320, 2))+1000;
  sx= sx+1;
  fill( 255,255,0 );
  ellipse( sx, sy, 40,40 );  
  if (sx > width+50){
    state = 1;
    sx = -50;
  }
  if (sx >-20 && sx<80){
    dark = dark -1;
  }
  if (sx >560 && sx<660){
    dark = dark +1;
  }
}

void drawMoon(){
  my = -sqrt(pow(1000,2)-pow(mx-320, 2))+1000;
  mx= mx+1;
  fill( 255,255,255 );
  ellipse( mx, my, 40,40 );  
  if (mx > width+50){
    state = 0;
    mx = -50;
 }
}