size(500,100);
background(255);
strokeWeight(5);
smooth();

int step = 10;
float lastX = -999;
float lastY = -999;

float y = 50;
int borderX = 20;
int borderY = 20;
for( int x = borderX; x  -999) {
    line(x, y, lastX, lastY);
  }
  lastX = x;
  lastY = y;
}