How do I draw lines using XNA?

Question

I\'ve read a bunch of tutorials involving XNA (and it\'s various versions) and I still am a little confused on drawing primitives. Everything seems to be really convoluted.

Answer 1

I encountered this problem my self and decided to make a class called LineBatch. LineBatch will draw lines without needing a spriteBatch or dots. The class is below.

public class LineBatch
{
    bool cares_about_begin_without_end;
    bool began;
    GraphicsDevice GraphicsDevice;
    List verticies = new List();
    BasicEffect effect;
    public LineBatch(GraphicsDevice graphics)
    {
        GraphicsDevice = graphics;
        effect = new BasicEffect(GraphicsDevice);
        Matrix world = Matrix.Identity;
        Matrix view = Matrix.CreateTranslation(-GraphicsDevice.Viewport.Width / 2, -GraphicsDevice.Viewport.Height / 2, 0);
        Matrix projection = Matrix.CreateOrthographic(GraphicsDevice.Viewport.Width, -GraphicsDevice.Viewport.Height, -10, 10);
        effect.World = world;
        effect.View = view;
        effect.VertexColorEnabled = true;
        effect.Projection = projection;
        effect.DiffuseColor = Color.White.ToVector3();
        cares_about_begin_without_end = true;
    }
    public LineBatch(GraphicsDevice graphics, bool cares_about_begin_without_end)
    {
        this.cares_about_begin_without_end = cares_about_begin_without_end;
        GraphicsDevice = graphics;
        effect = new BasicEffect(GraphicsDevice);
        Matrix world = Matrix.Identity;
        Matrix view = Matrix.CreateTranslation(-GraphicsDevice.Viewport.Width / 2, -GraphicsDevice.Viewport.Height / 2, 0);
        Matrix projection = Matrix.CreateOrthographic(GraphicsDevice.Viewport.Width, -GraphicsDevice.Viewport.Height, -10, 10);
        effect.World = world;
        effect.View = view;
        effect.VertexColorEnabled = true;
        effect.Projection = projection;
        effect.DiffuseColor = Color.White.ToVector3();
    }
    public void DrawAngledLineWithRadians(Vector2 start, float length, float radians, Color color)
    {
        Vector2 offset = new Vector2(
            (float)Math.Sin(radians) * length, //x
            -(float)Math.Cos(radians) * length //y
            );
        Draw(start, start + offset, color);
    }
    public void DrawOutLineOfRectangle(Rectangle rectangle, Color color)
    {
        Draw(new Vector2(rectangle.X, rectangle.Y), new Vector2(rectangle.X + rectangle.Width, rectangle.Y), color);
        Draw(new Vector2(rectangle.X, rectangle.Y), new Vector2(rectangle.X, rectangle.Y + rectangle.Height), color);
        Draw(new Vector2(rectangle.X + rectangle.Width, rectangle.Y), new Vector2(rectangle.X + rectangle.Width, rectangle.Y + rectangle.Height), color);
        Draw(new Vector2(rectangle.X, rectangle.Y + rectangle.Height), new Vector2(rectangle.X + rectangle.Width, rectangle.Y + rectangle.Height), color);
    }
    public void DrawOutLineOfTriangle(Vector2 point_1, Vector2 point_2, Vector2 point_3, Color color)
    {
        Draw(point_1, point_2, color);
        Draw(point_1, point_3, color);
        Draw(point_2, point_3, color);
    }
    float GetRadians(float angleDegrees)
    {
        return angleDegrees * ((float)Math.PI) / 180.0f;
    }
    public void DrawAngledLine(Vector2 start, float length, float angleDegrees, Color color)
    {
        DrawAngledLineWithRadians(start, length, GetRadians(angleDegrees), color);
    }
    public void Draw(Vector2 start, Vector2 end, Color color)
    {
        verticies.Add(new VertexPositionColor(new Vector3(start, 0f), color));
        verticies.Add(new VertexPositionColor(new Vector3(end, 0f), color));
    }
    public void Draw(Vector3 start, Vector3 end, Color color)
    {
        verticies.Add(new VertexPositionColor(start, color));
        verticies.Add(new VertexPositionColor(end, color));
    }
    public void End()
    {
        if (!began)
            if (cares_about_begin_without_end)
                throw new ArgumentException("Please add begin before end!");
            else
                Begin();
        if (verticies.Count > 0)
        {
            VertexBuffer vb = new VertexBuffer(GraphicsDevice, typeof(VertexPositionColor), verticies.Count, BufferUsage.WriteOnly);
            vb.SetData(verticies.ToArray());
            GraphicsDevice.SetVertexBuffer(vb);

            foreach (EffectPass pass in effect.CurrentTechnique.Passes)
            {
                pass.Apply();
                GraphicsDevice.DrawPrimitives(PrimitiveType.LineList, 0, verticies.Count / 2);
            }
        }
        began = false;
    }
    public void Begin()
    {
        if (began)
            if (cares_about_begin_without_end)
                throw new ArgumentException("You forgot end.");
            else
                End();
        verticies.Clear();
            began = true;
    }
}