VCS/AstroSim3 - Sample is best!

開発環境	Microsoft Visual C# 2010 Express (SP1)
実行環境	Microsoft Windows XP Home Edition (SP3)
プロジェクトの種類	Windows Game (4.0)
プロジェクト名	AstroSim1

Game1.cs

/*
 * 太陽年を春分点の平均回帰年とし、365.24219日(365d5h48m45s)を採用する。
 * 黄道傾斜角（地球の赤道傾斜角）を23deg26m21.406s(=84381.406s) 2000/01/01 12:00(UT)とする。
 */
using System;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;
using Microsoft.Xna.Framework.Input;
 
namespace AstroSim1
{
    class Game1 : Game
    {
        GraphicsDeviceManager graphics;
        SpriteBatch sprite;
        SpriteFont font;
        BasicEffect effect;
        VertexBuffer vertexBuffer;
        //IndexBuffer indexBuffer;
 
        const double au = 149597870700; // 天文単位(m)
        const double Sr = 1392000 / 2; // 太陽の半径(km)
        const double solarYear = 365.24219; // 太陽年(day)
        const double obliquity = 84381.406; // 黄道傾斜角(degsec)
        const double siderealDay = 86164.091; // 恒星日(s)
 
        float camDist = (float)(au * 3);
        float camLat = 0;
 
        public Game1()
        {
            graphics = new GraphicsDeviceManager(this);
            graphics.PreferredBackBufferWidth = 1280;
            graphics.PreferredBackBufferHeight = 720;
            Content.RootDirectory = "Content";
            IsMouseVisible = true;
        }
 
        protected override void LoadContent()
        {
            sprite = new SpriteBatch(GraphicsDevice);
            font = Content.Load<SpriteFont>("SpriteFont1");
 
            effect = new BasicEffect(GraphicsDevice);
            effect.VertexColorEnabled = true;
            //effect.Projection = Matrix.CreatePerspectiveFieldOfView(MathHelper.ToRadians(45),
            //    GraphicsDevice.Viewport.AspectRatio, (float)au, (float)(au * 5));
            effect.Projection = Matrix.CreateOrthographic(
                camDist * GraphicsDevice.Viewport.AspectRatio, camDist, (float)au, (float)(au * 5));
 
            VertexPositionColor[] vertices = new VertexPositionColor[(360 + 1) * 3];
 
            double radObliq = obliquity * Math.PI / (180 * 60 * 60);
            double cosObliq = Math.Cos(radObliq);
            double sinObliq = Math.Sin(radObliq);
 
            for (int t = 0; t <= 360; t++)
            {
                float rad = MathHelper.ToRadians(t);
                float x = (float)(Math.Cos(rad) * au);
                float r = (float)(Math.Sin(rad) * au);
                float y = (float)cosObliq * r;
                float z = (float)sinObliq * r;
                vertices[0 + t] = new VertexPositionColor(
                    new Vector3(x, r, 0), Color.Red); // 黄道傾斜角=0(天の赤道面)
                vertices[361 + t] = new VertexPositionColor(
                    new Vector3(x, y, z), Color.Yellow); // 黄道
                vertices[722 + t] = new VertexPositionColor(
                    new Vector3(x, y, 0), Color.Cyan); // 黄道を天の赤道面に投影
            }
 
            vertexBuffer = new VertexBuffer(GraphicsDevice,
                typeof(VertexPositionColor), vertices.Length, BufferUsage.WriteOnly);
            vertexBuffer.SetData(vertices);
 
            // 黄道傾斜角が南中時間に与える影響
            int solarYearSec = (int)(solarYear * 24 * 60 * 60); // 太陽年(s)
            int[] culmination = new int[365 + 1]; // 南中(正中)
            int day = 0;
 
            for (int t = 0; t < solarYearSec; t++)
            {
                // 地球を基準とした太陽の公転
                double rad = (2 * Math.PI) * t / solarYearSec;
                double x = Math.Cos(rad) * au;
                double r = Math.Sin(rad) * au;
                double y = cosObliq * r;
                //double z = sinObliq * r;
                double radCelestialEquator = Math.Atan2(y, x); // 天の赤道上の角度
                if (radCelestialEquator < 0) radCelestialEquator += (2 * Math.PI);
 
                // 地球の自転
                double radEarthRotation = (2 * Math.PI) * ((t / siderealDay) % 1.0);
                if (radCelestialEquator <= radEarthRotation)
                {
                    culmination[day++] = t;
                    t += 86164; // 1回転する間は追い越さないので飛ばす
                }
            }
            for (int i = 0; i < culmination.Length; i++)
            {
                Console.WriteLine(string.Format("{0} {1}", i, new TimeSpan(0, 0, culmination[i])));
            }
 
            base.LoadContent();
        }
 
        protected override void Update(GameTime gameTime)
        {
            KeyboardState kState = Keyboard.GetState();
            if (kState.IsKeyDown(Keys.Escape)) Exit();
            if (kState.IsKeyDown(Keys.Up)) camLat = Math.Min(camLat + 1, 89.9f);
            if (kState.IsKeyDown(Keys.Down)) camLat = Math.Max(camLat - 1, -89.9f);
            base.Update(gameTime);
        }
 
        protected override void Draw(GameTime gameTime)
        {
            GraphicsDevice.Clear(Color.CornflowerBlue);
            GraphicsDevice.BlendState = BlendState.AlphaBlend;
 
            // カメラ
            float rad = MathHelper.ToRadians(camLat);
            float x = (float)Math.Cos(rad) * camDist;
            float z = (float)Math.Sin(rad) * camDist;
            effect.View = Matrix.CreateLookAt(
                new Vector3(x, 0, z), Vector3.Zero, Vector3.UnitZ);
 
            GraphicsDevice.SetVertexBuffer(vertexBuffer);
            foreach (EffectPass pass in effect.CurrentTechnique.Passes)
            {
                pass.Apply();
                GraphicsDevice.DrawPrimitives(PrimitiveType.LineStrip, 0, 360);
                GraphicsDevice.DrawPrimitives(PrimitiveType.LineStrip, 361, 360);
                GraphicsDevice.DrawPrimitives(PrimitiveType.LineStrip, 722, 360);
            }
 
            sprite.Begin();
            string text = string.Format("lat={0:f0}", camLat);
            sprite.DrawString(font, text, new Vector2(0, 0), Color.White);
            sprite.End();
 
            base.Draw(gameTime);
        }
    }
}