acdream/src/AcDream.App/Rendering/FlyCamera.cs

// src/AcDream.App/Rendering/FlyCamera.cs
using System.Numerics;

namespace AcDream.App.Rendering;

public sealed class FlyCamera : ICamera
{
    public Vector3 Position { get; set; } = new(96, 96, 150);
    public float Yaw { get; set; } = MathF.PI / 2f;  // facing +Y
    public float Pitch { get; set; } = -0.3f;         // looking slightly down
    public float FovY { get; set; } = MathF.PI / 3f;
    public float Aspect { get; set; } = 16f / 9f;

    /// <summary>
    /// Default move speed in world units per second. AC's character walks
    /// at ~4 u/s and runs at ~7 u/s; 12 here is comfortable for navigating
    /// scenery without overshooting and roughly tracks a fast jog. Hold
    /// shift while moving to enter "boost" mode at <see cref="BoostSpeed"/>.
    /// </summary>
    public float MoveSpeed { get; set; } = 12f;
    public float BoostSpeed { get; set; } = 50f;
    public float MouseSensitivity { get; set; } = 0.003f;

    private const float PitchLimit = 1.5533f;  // ~89 degrees

    public Matrix4x4 View
    {
        get
        {
            var forward = Forward();
            return Matrix4x4.CreateLookAt(Position, Position + forward, Vector3.UnitZ);
        }
    }

    public Matrix4x4 Projection
        => Matrix4x4.CreatePerspectiveFieldOfView(FovY, Aspect, 1f, 5000f);

    /// <summary>
    /// Integrate position for one frame based on WASD + vertical keys.
    /// W/S move forward/back in the horizontal plane (ignoring pitch).
    /// A/D strafe left/right. Up/down translate along world Z.
    /// </summary>
    public void Update(double dt, bool w, bool a, bool s, bool d, bool up, bool down, bool boost = false)
    {
        float speed = boost ? BoostSpeed : MoveSpeed;
        float step = (float)(speed * dt);

        // Forward in the horizontal plane (ignore pitch so W doesn't dive into ground).
        var flatForward = new Vector3(MathF.Cos(Yaw), MathF.Sin(Yaw), 0f);
        var right = new Vector3(MathF.Sin(Yaw), -MathF.Cos(Yaw), 0f);

        if (w) Position += flatForward * step;
        if (s) Position -= flatForward * step;
        if (a) Position -= right * step;
        if (d) Position += right * step;
        if (up) Position += Vector3.UnitZ * step;
        if (down) Position -= Vector3.UnitZ * step;
    }

    /// <summary>
    /// Apply accumulated mouse deltas (pixels since last frame). Positive deltaX
    /// rotates the view to the right (decreases yaw), positive deltaY rotates
    /// down (decreases pitch).
    /// </summary>
    public void Look(float deltaX, float deltaY)
    {
        Yaw -= deltaX * MouseSensitivity;
        Pitch = Math.Clamp(Pitch - deltaY * MouseSensitivity, -PitchLimit, PitchLimit);
    }

    private Vector3 Forward()
    {
        float cp = MathF.Cos(Pitch);
        return new Vector3(
            cp * MathF.Cos(Yaw),
            cp * MathF.Sin(Yaw),
            MathF.Sin(Pitch));
    }
}