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, 1920 / 4, 1080 / 4);
    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 int Bottom { get => bbox.Bottom; }

    public Point HalfSize { get => new Point(Width / 2, Height / 2); }

    private readonly Random random = new Random();
    private float shakeTime = 0.0f;

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

    public void Update(float modelTime, Player player, int worldWidth, int worldHeight) {
      Vector2 pos = player.Position;
      float xDiff = pos.X - bbox.Center.X;
      float yDiff = pos.Y - bbox.Center.Y;
      if (Math.Abs(xDiff) > 16) {
        bbox.Offset((int) (xDiff * 0.1), 0);
      }
      if (player.StandingOnGround) {
        bbox.Offset(0, (int) (yDiff * 0.1));
      }
      if (yDiff > 16) {
        bbox.Offset(0, (int) (yDiff * 0.2));
      }
      if (bbox.Left < 0) {
        bbox.Offset(-bbox.Left, 0);
      }
      if (bbox.Right > worldWidth) {
        bbox.Offset(worldWidth - bbox.Right, 0);
      }
      if (bbox.Top < 0) {
        bbox.Offset(0, -bbox.Top);
      }
      if (bbox.Bottom > worldHeight) {
        bbox.Offset(0, worldHeight - bbox.Bottom);
      }
      if (shakeTime > 0) {
        shakeTime -= modelTime;
        int x = random.Next(-4, 5);
        int y = random.Next(-4, 5);
        bbox.Offset(x, y);
      }
      Debug.AddToast($"p: {pos.X}, {pos.Y} c: {bbox.Center.X}");
    }

    public void Shake() {
      shakeTime = 0.3f;
    }
  }
}