/* * * * * * * * * * * * * * * * * * * * * * * * * * 
 * Renders 2D primitives (lines) specified in screen/pixel space
 * using an instance of BasicEffect.
 * 
 * By Karn Bianco - www.KarnBianco.co.uk
 * 
 * * * * * * * * * * * * * * * * * * * * * * * * * */

using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;

namespace NamespaceGoesHere
{
    public class Render2DLines : Microsoft.Xna.Framework.Game
    {
        GraphicsDeviceManager graphics;

        Vector2[] vertices;                     // Vertices defined in screen space
        VertexPositionColor[] verticesForGPU;   // 3D vertices required for rendering
        int[] indices;                          // Indices for defining lines from points
        BasicEffect basicEffect;                // BasicEffect instance

        public Render2DLines()
        {
            graphics = new GraphicsDeviceManager(this);
            Content.RootDirectory = "Content";

            this.graphics.PreferredBackBufferWidth = 450;
            this.graphics.PreferredBackBufferHeight = 300;
        }

        protected override void LoadContent()
        {
            // Create a new instance of BasicEffect
            basicEffect = new BasicEffect(GraphicsDevice, null);

            // Set up vertices in screen space (just as you would set sprite positions)
            vertices = new Vector2[4];
            vertices[0] = new Vector2(10, 10);
            vertices[1] = new Vector2(400, 10);
            vertices[2] = new Vector2(400, 150);
            vertices[3] = new Vector2(10, 150);

            // Set up 3D vertices using screen space vectors and a 0 component for z-value
            verticesForGPU = new VertexPositionColor[4];

            for (int i = 0; i < vertices.Length; i++)
			{
                verticesForGPU[i].Position = new Vector3(
                    vertices[i].X / GraphicsDevice.PresentationParameters.BackBufferWidth * 2.0f - 1.0f,
                    vertices[i].Y / GraphicsDevice.PresentationParameters.BackBufferHeight * -2.0f + 1.0f, 0);
                verticesForGPU[i].Color = Color.White;
			}

            // Generate two indices for each vertex
            indices = new int[8] { 0, 1, 1, 2, 2, 3, 3, 0 };

            // Set vertex declaration
            GraphicsDevice.VertexDeclaration = new VertexDeclaration(
                GraphicsDevice, VertexPositionColor.VertexElements);
        }

        protected override void Update(GameTime gameTime)
        {
            base.Update(gameTime);
        }

        protected override void Draw(GameTime gameTime)
        {
            GraphicsDevice.Clear(Color.Black);

            // Renders lines using color component of VertexPositionColor
            basicEffect.VertexColorEnabled = true;

            basicEffect.Begin();         
            basicEffect.CurrentTechnique.Passes[0].Begin();

            GraphicsDevice.DrawUserIndexedPrimitives(PrimitiveType.LineList, verticesForGPU, 0,
                verticesForGPU.Length, indices, 0, indices.Length / 2); // Draw lines

            basicEffect.CurrentTechnique.Passes[0].End();
            basicEffect.End();

            base.Draw(gameTime);
        }
    }
}