sneak/Shared/Camera.cs

using Microsoft.Xna.Framework;
using System;

// Good background reading, eventually:
// https://gamasutra.com/blogs/ItayKeren/20150511/243083/Scroll_Back_The_Theory_and_Practice_of_Cameras_in_SideScrollers.php
namespace SemiColinGames {
  public class Camera {
    // Screen size in pixels is 1920x1080 divided by 4.
    private Rectangle bbox = new Rectangle(0, 0, 480, 270);
    public int Width { get => bbox.Width; }
    public int Height { get => bbox.Height; }
    public int Left { get => bbox.Left; }
    public int Top { get => bbox.Top; }
    public Point HalfSize { get => new Point(Width / 2, Height / 2); }

    public Matrix Projection {
      get => Matrix.CreateOrthographicOffCenter(Left, Left + Width, Height, 0, -1, 1);
    }

    public void Update(Point player, int worldWidth) {
      int diff = player.X - bbox.Center.X;
      if (Math.Abs(diff) > 16) {
        bbox.Offset((int) (diff * 0.1), 0);
      }
      if (bbox.Left < 0) {
        bbox.Offset(-bbox.Left, 0);
      }
      if (bbox.Right > worldWidth) {
        bbox.Offset(worldWidth - bbox.Right, 0);
      }
      Debug.AddToast($"p: {player.X}, {player.Y} c: {bbox.Center.X}");
    }
  }
}