Hello everyone,

I started to implement a basic physics engine in my game, and I just want someone to look at my code and see if I did it right. I think I did, but it never hurts to have someone look at it.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

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;

using Engine.ContentManger;

namespace TestEngine.CollitionDetection
{
    class MovingObject
    {
        GraphicsDeviceManager Graphics;

        Texture2D Texture;
        Vector2 Position, Size, Velocity, Acceleration;
        float Speed, Resistance;
        Rectangle Rec;

        KeyboardState keyboardState;

        public MovingObject()
        {
            Position = Vector2.Zero;
            Size = new Vector2(32, 32);
        }

        public void Initialize(GraphicsDeviceManager Graphics)
        {
            this.Graphics = Graphics;
        }

        public void LoadContent()
        {
            Texture = StreamTexture.LoadTextureFromStream(Graphics, "Content/test.png");
        }

        public void Update(GameTime gameTime)
        {
            Speed = 0.0005f * (float)gameTime.ElapsedGameTime.TotalMilliseconds;
            Resistance = 0.0001f * (float)gameTime.ElapsedGameTime.TotalMilliseconds;;

            keyboardState = Keyboard.GetState();

            if (keyboardState.IsKeyDown(Keys.W))
                Acceleration.Y -= Speed;
            else if (Acceleration.Y < 0)
                Acceleration.Y += Resistance;

            if (keyboardState.IsKeyDown(Keys.S))
                Acceleration.Y += Speed;
            else if (Acceleration.Y > 0)
                Acceleration.Y -= Resistance;

            if (keyboardState.IsKeyDown(Keys.D))
                Acceleration.X += Speed;
            else if (Acceleration.X > 0)
                Acceleration.X -= Resistance;

            if (keyboardState.IsKeyDown(Keys.A))
                Acceleration.X -= Speed;
            else if (Acceleration.X < 0)
                Acceleration.X += Resistance;

            Velocity += Acceleration;

            Rec = new Rectangle((int)(Position.X + Velocity.X), (int)(Position.Y + Velocity.Y), (int)Size.X, (int)Size.Y);
        }

        public void Draw(SpriteBatch spriteBatch)
        {
            spriteBatch.Draw(Texture, Rec, Color.White);
        }
    }
}

*Short back story about me and physics in high school, not impotent to read *

I always had trouble with physics in high school and I never understood it very well. So I decided to make my own physics engine in my game and I think I'm doing well. After reading some articles about physics 101 and watching some videos on Youtube, I started to fall in love with physics and I started to wonder why I had such a hard time understanding physics in high school. I guess I didn't have the option to implement basic physics in a game and tinker with the variables and see how they moved and reacted in high school.

You forgot the algebra classes.

The X and Y are vector elements. The Vector2 class should have a overloaded operator instead of multiplying, subtracting, etc. each element individually; most of the material you find about physics or graphics programming uses vector operations which is the same as vector elements operations to teach its subject.

Vector2 linearPosition;

Vector2 linearVelocity;

Vector2 linearAcceleration;

Vector2 linearForce = gravity;

float objectMass = x;

float deltaTime = 1 / 60.0 (60 FPS if your computer is capable)

linearAcceleration = linearForce / objectMass;

linearVelocity += linearAcceleration * deltaTime;

linearPosition += linearVelocity * deltaTime;

It looks like speed should be called Force. You're applying it to the acceleration which means it's a sort of force. Velocity already contains your speed. Just a little note.