encompass-cs-docs/content/concepts/world.md

title	date	weight
World	2019-05-22T12:51:08-07:00	100

World is the pie crust that contains all the delicious Encompass ingredients together.

The World's Update function drives the simulation and should be controlled from your engine's update loop.

The World's Draw function tells the Renderers to draw the scene.

In FNA, the game loop looks something like this:

using Encompass;
using Microsoft.Xna.Framework;

public class MyGame : Game
{
    private World world;
    SpriteBatch spriteBatch;

    RenderTarget2D gameRenderTarget;
    RenderTarget2D levelBrowserRenderTarget;
    RenderTarget2D uiRenderTarget;

    ...

    /// <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>
    protected override void Update(GameTime gameTime)
    {
        if (GamePad.GetState(Microsoft.Xna.Framework.PlayerIndex.One).Buttons.Back == ButtonState.Pressed || Keyboard.GetState().IsKeyDown(Keys.Escape))
            Exit();

        world.Update(gameTime.ElapsedGameTime.TotalSeconds);

        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)
    {
        world.Draw();

        GraphicsDevice.SetRenderTarget(null);

        spriteBatch.Begin(SpriteSortMode.Deferred, null, SamplerState.PointClamp);
        spriteBatch.Draw(gameRenderTarget, windowDimensions, Color.White);
        spriteBatch.Draw(levelBrowserRenderTarget, windowDimensions, Color.White);
        spriteBatch.Draw(uiRenderTarget, windowDimensions, Color.White);
        spriteBatch.End();

        base.Draw(gameTime);
    }
}

But you can call these methods wherever you see fit.

{{% notice tip %}} It is valid for your game to have multiple Worlds, but be warned that it is difficult to share information between Worlds by design and this may not be a good choice. {{% /notice %}}

What's that whole gameTime business about?

gameTime lets us utilize the concept of delta-time. Delta-time means that we take into account the amount of time that has elapsed between frames. Correct usage of delta-time is crucial to make sure that your game does not become frame-dependent, which is very bad. We'll talk more about frame-dependence later in the tutorial, but to briefly summarize, if your game is frame-dependent you will run into very frustrating behavior if you ever want your game to run at a different framerate than the one you are developing with.

Even if you lock your game to a fixed timestep (which can be a very good idea for achieving precise game physics), writing your game with delta-time in mind can be the difference between changing the timestep being a one-line tweak or a months long hair-pulling nightmare.

That's it! Now that we have these high-level concepts down, let's build an actual, for-real game.