static void drawRoundEdgeLine(BufferedImage image, int x1, int y1, int x2, int y2, Color color, float width) {
  Graphics2D g = imageGraphics(image);
  g.setColor(color);
  g.setStroke(new BasicStroke(width, BasicStroke.CAP_ROUND, BasicStroke.JOIN_MITER));
  g.drawLine(x1, y1, x2, y2);
  g.dispose();
}

static void drawRoundEdgeLine(BufferedImage image, Pt a, Pt b, Color color, float width) {
  drawRoundEdgeLine(image, a.x, a.y, b.x, b.y, color, width);
}