How can I draw a simple 2D line in XNA without using 3D primitives and shders

Question

I would like to be able to draw arbitary lines in my sprite based 2D XNA game. How can I draw a simple line on screen in XNA without dealing with vertex arrays or shaders.

Answer 1

You can draw a line using sprites. SpriteBatch.Draw(...) helpfully allows us to strech and rotate a sprite(texture).

In this code, we take a 1x1 pixel texture, strech it (by defining a rectangle of the correct shape and rotate it so it looks like a line.

    Texture2D t; //base for the line texture


    protected override void LoadContent()
    {
        spriteBatch = new SpriteBatch(GraphicsDevice);
        // create 1x1 texture for line drawing
        t = new Texture2D(GraphicsDevice, 1, 1);
        t.SetData<Color>(
            new Color[] { Color.White });// fill the texture with white
    }


    protected override void Draw(GameTime gameTime)
    {


        GraphicsDevice.Clear(Color.CornflowerBlue);

        spriteBatch.Begin();
        DrawLine(spriteBatch, //draw line
            new Vector2(200, 200), //start of line
            new Vector2(100, 50) //end of line
        );
        spriteBatch.End();



        base.Draw(gameTime);
    }


    void DrawLine(SpriteBatch sb, Vector2 start, Vector2 end)
    {
        Vector2 edge = end - start;
        // calculate angle to rotate line
        float angle =
            (float)Math.Atan2(edge.Y , edge.X);


        sb.Draw(t,
            new Rectangle(// rectangle defines shape of line and position of start of line
                (int)start.X,
                (int)start.Y,
                (int)edge.Length(), //sb will strech the texture to fill this rectangle
                1), //width of line, change this to make thicker line
            null,
            Color.Red, //colour of line
            angle,     //angle of line (calulated above)
            new Vector2(0, 0), // point in line about which to rotate
            SpriteEffects.None,
            0);

    }

Answer 2

This library: http://sourceforge.net/projects/primitives2d/ has worked well for me in the past.