float P0x = 10., P0y = 10.;
float P1x = 10., P1y = 40.;
float P2x = 40., P2y = 60.;
float P3x = 80., P3y = 20.;

noFill();
bezier(P0x,P0y,P1x,P1y,P2x,P2y,P3x,P3y);
rectMode(CENTER);
rect(P0x,P0y,5,5);
rect(P1x,P1y,5,5);
rect(P2x,P2y,5,5);
rect(P3x,P3y,5,5);