Thursday, January 6, 2011

XNA Tutorial: Simulate Gravity [Jumping Ball] #1

Here is the code

using System;
using System.Collections.Generic;
using System.Linq;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Audio;
using Microsoft.Xna.Framework.Content;
using Microsoft.Xna.Framework.GamerServices;
using Microsoft.Xna.Framework.Graphics;
using Microsoft.Xna.Framework.Input;
using Microsoft.Xna.Framework.Media;

namespace FallingBall
{
    /// <summary>
    /// This is the main type for your game
    /// </summary>
    public class Game1 : Microsoft.Xna.Framework.Game
    {
        GraphicsDeviceManager graphics;
        SpriteBatch spriteBatch;
        Texture2D ball; Vector2 ballpos = Vector2.Zero; // The position of the ball in 2D space (X,Y)
        public Game1()
        {
            graphics = new GraphicsDeviceManager(this);
            // Set the window height and width
            graphics.PreferredBackBufferWidth = 1024;
            graphics.PreferredBackBufferHeight = 920;
            Content.RootDirectory = "Content";
        }

        /// <summary>
        /// Allows the game to perform any initialization it needs to before starting to run.
        /// This is where it can query for any required services and load any non-graphic
        /// related content.  Calling base.Initialize will enumerate through any components
        /// and initialize them as well.
        /// </summary>
        protected override void Initialize()
        {
            // TODO: Add your initialization logic here

            base.Initialize();
        }

        /// <summary>
        /// LoadContent will be called once per game and is the place to load
        /// all of your content.
        /// </summary>
        protected override void LoadContent()
        {
            // Create a new SpriteBatch, which can be used to draw textures.
            spriteBatch = new SpriteBatch(GraphicsDevice);
            ball = Content.Load<Texture2D>("ball");
            ballpos.X = graphics.GraphicsDevice.Viewport.Width / 2 - ball.Width / 2; // Place the ball in the middle
            ballpos.Y = graphics.GraphicsDevice.Viewport.Height - ball.Height; // Place the ball on the bottom side of the window | the ground
            // TODO: use this.Content to load your game content here
        }

        /// <summary>
        /// UnloadContent will be called once per game and is the place to unload
        /// all content.
        /// </summary>
        protected override void UnloadContent()
        {
            // TODO: Unload any non ContentManager content here
        }

        /// <summary>
        /// Allows the game to run logic such as updating the world,
        /// checking for collisions, gathering input, and playing audio.
        /// </summary>
        /// <param name="gameTime">Provides a snapshot of timing values.</param>
        //----------------------------------------------------------------------//
        double vi, t = 0; // vi - initial velocity | t - time
        double g = 520; // pixels per second squared | gravitational acceleration
        int keyState = 0;
        //----------------------------------------------------------------------//
        protected override void Update(GameTime gameTime)
        {
            // Allows the game to exit
            if (Keyboard.GetState().IsKeyDown(Keys.Escape))
                this.Exit();
            else if (Keyboard.GetState().IsKeyDown(Keys.Space))
            {
                keyState = 1; vi = -820; // set a velocity of -820 pixels per second
            }
            if (keyState == 1)
            {
                // the normal formula is: vi * t - g * t^2 / 2 and vi is positive, but here UP means decrease Y and DOWN means increase Y
                // that's why it looks strange
                ballpos.Y = (float)(vi * t + g * t * t / 2) + graphics.GraphicsDevice.Viewport.Height - ball.Height;
                t = t + gameTime.ElapsedGameTime.TotalSeconds; // calculate the time since the ball has left the ground
            }
            if (ballpos.Y > graphics.GraphicsDevice.Viewport.Height - ball.Height) // Don't allow the ball to go beyond the bottom side of the window
            {
                ballpos.Y = graphics.GraphicsDevice.Viewport.Height - ball.Height;
                keyState = 0;
                t = 0;
            }

            base.Update(gameTime);
        }

        /// <summary>
        /// This is called when the game should draw itself.
        /// </summary>
        /// <param name="gameTime">Provides a snapshot of timing values.</param>
        protected override void Draw(GameTime gameTime)
        {
            GraphicsDevice.Clear(Color.CornflowerBlue);
            // Draw the ball
            spriteBatch.Begin(SpriteSortMode.FrontToBack, BlendState.AlphaBlend);
            spriteBatch.Draw(ball, ballpos, Color.White);
            spriteBatch.End(); 

            base.Draw(gameTime);
        }
    }
}

Or download the solution

No comments:

Post a Comment