I am drawing a line in XNA which I want to never end. I also have a tool that moves forward in X-direction and a camera which is centered at this tool. However, when I reach the end of the viewport the lines are not drawn anymore. Here are some pictures to illustrate my problem:

At the start the line goes across the whole screen, but as my tool moves forward, we reach the end of the line.

Here are the method which draws the lines:

        private void DrawEvenlySpacedSprites (Texture2D texture, Vector2 point1, Vector2 point2, float increment)
{
    var distance = Vector2.Distance (point1, point2);    // the distance between two points
    var iterations = (int)(distance / increment);       // how many sprites with be drawn
    var normalizedIncrement = 1.0f / iterations;        // the Lerp method needs values between 0.0 and 1.0
    var amount = 0.0f;

    if (iterations == 0)
        iterations = 1;

    for (int i = 0; i < iterations; i++) {
        var drawPoint = Vector2.Lerp (point1, point2, amount);
        spriteBatch.Draw (texture, drawPoint, Color.White);
        amount += normalizedIncrement;
    }
}

Here are the draw method in Game. The dots are my lines:

protected override void Draw (GameTime gameTime)
{
    graphics.GraphicsDevice.Clear(Color.Black);
    nyVector = nextVector (gammelVector);
    GraphicsDevice.SetRenderTarget (renderTarget);
    spriteBatch.Begin ();
    DrawEvenlySpacedSprites (dot, gammelVector, nyVector, 0.9F);
    spriteBatch.End ();

    GraphicsDevice.SetRenderTarget (null);
    spriteBatch.Begin (SpriteSortMode.Deferred, BlendState.AlphaBlend, null, null, null, null, camera.transform);
    spriteBatch.Draw (renderTarget, new Vector2 (), Color.White);
    spriteBatch.Draw (tool, new Vector2(toolPos.X - (tool.Width/2), toolPos.Y - (tool.Height/2)), Color.White);
    spriteBatch.End ();

    gammelVector = new Vector2 (nyVector.X, nyVector.Y);
    base.Draw (gameTime);
}

Here's the next vector-method, It just finds me a new point where the line should be drawn with a new X-coordinate between 100 and 200 pixels and a random Y-coordinate between the old vector Y-coordinate and the height of the viewport:

        Vector2 nextVector (Vector2 vector)
    {
        return new Vector2 (vector.X + r.Next(100, 200), r.Next ((int)(vector.Y - 100), viewport.Height));
    }

Can anyone point me in the right direction here? I'm guessing it has to do with the viewport.width, but I'm not quite sure how to solve it. Thank you for reading!