问如何根据行程帽计算从哪里开始我的线路？

EN

private void initialize() {
    this.paint = new Paint();
    this.paint.setColor(Color.BLACK);
    this.paint.setStyle(Paint.Style.STROKE);
    this.paint.setStrokeCap(Paint.Cap.ROUND);
    this.paint.setStrokeWidth(1);
}

public void setStrokeWidth(float strokeWidth) {
    this.paint.setStrokeWidth(strokeWidth);
}

public void onDraw(Canvas canvas) {
    int x_start, x_end, y, cap_width;
    y = this.getHeight() / 2;
    x_start = cap_width; //Need to compensate for cap.
    x_end = this.getWidth() - cap_width; //Need to compensate for cap.

    canvas.drawLine(x_start, y, x_end, y, paint);
}