How do I draw lines using XNA?

Following NoHayProblema's answer (I cannot comment yet).

That answer, although the correct one for this old question, is incomplete. Texture2D constructor returns an uninitialized texture, which is never painted on screen. In order to use that approach, you need to set the texture's data like this:

Texture2D SimpleTexture = new Texture2D(GraphicsDevice, 1, 1, false,
    SurfaceFormat.Color);

Int32[] pixel = {0xFFFFFF}; // White. 0xFF is Red, 0xFF0000 is Blue
SimpleTexture.SetData<Int32> (pixel, 0, SimpleTexture.Width * SimpleTexture.Height);

// Paint a 100x1 line starting at 20, 50
this.spriteBatch.Draw(SimpleTexture, new Rectangle(20, 50, 100, 1), Color.Blue);

Take into account that the way you write the data into pixel must be consistent with the texture's SurfaceFormat. The example works because the texture is being formatted as RGB. Rotations can be applied in spriteBatch.Draw like this:

this.spriteBatch.Draw (SimpleTexture, new Rectangle(0, 0, 100, 1), null,
    Color.Blue, -(float)Math.PI/4, new Vector2 (0f, 0f), SpriteEffects.None, 1f);

found a tutorial for that http://www.bit-101.com/blog/?p=2832

its using a BasicEffect (shader) and the built in draw user primitive in XNA 4.0

some code samples i find helpful:

load content method

basicEffect = new BasicEffect(GraphicsDevice);
basicEffect.VertexColorEnabled = true;
basicEffect.Projection = Matrix.CreateOrthographicOffCenter
(0, GraphicsDevice.Viewport.Width,     // left, right
GraphicsDevice.Viewport.Height, 0,    // bottom, top
0, 1);   

draw method

basicEffect.CurrentTechnique.Passes[0].Apply();
var vertices = new VertexPositionColor[4];
vertices[0].Position = new Vector3(100, 100, 0);
vertices[0].Color = Color.Black;
vertices[1].Position = new Vector3(200, 100, 0);
vertices[1].Color = Color.Red;
vertices[2].Position = new Vector3(200, 200, 0);
vertices[2].Color = Color.Black;
vertices[3].Position = new Vector3(100, 200, 0);
vertices[3].Color = Color.Red;

GraphicsDevice.DrawUserPrimitives<VertexPositionColor>(PrimitiveType.LineList, vertices, 0, 2);

have fun and vote up if this helped you. also pay a visit to the tutorial i got this from.

When working with XNA, everything (even 2d primitives) have to be expressed in a way that a 3d card can understand, which means that a line is just a set of vertices.

MSDN has a pretty good walkthrough here:

http://msdn.microsoft.com/en-us/library/bb196414.aspx#ID2EEF

You'll find that it takes more code to render a primitive line than it would take to just setup a textured quad and rotate that, since in essence, your doing the same thing when rendering a line.