Physics-Engine/PhysicsEngine/Graphics/Camera.cs

using Raylib_cs;
using System;
using System.Numerics;

namespace PhysicsEngine
{
    public class Camera
    {
        public const float PixelsPerMeter = 100.0f;
        private const float GridSpacing = 1.0f; // meters
        private const float ZoomLerpSpeed = 30.0f;
        private const float MoveLerpSpeed = 20.0f;
        private const float ZoomFactor = 0.1f;
        private const float MinZoom = 0.2f;
        private const float MaxZoom = 50.0f;

        public Camera2D RaylibCamera { get; private set; }
        public Vector2 Position => RaylibCamera.Target / PixelsPerMeter;
        public float Zoom => RaylibCamera.Zoom;

        private float targetZoom;
        private Vector2 targetPosition;
        private Vector2 dragStartMouseScreen;
        private Vector2 dragStartTarget;
        private bool isDragging = false;

        public Camera()
        {
            RaylibCamera = new Camera2D
            {
                Target = Vector2.Zero,
                Offset = new Vector2(Raylib.GetScreenWidth() / 2.0f, Raylib.GetScreenHeight() / 2.0f),
                Rotation = 0.0f,
                Zoom = 1.0f
            };

            targetZoom = 1.0f;
            targetPosition = RaylibCamera.Target;
        }

        public void Update(float frameTime)
        {
            Camera2D cam = RaylibCamera;
            cam.Offset = new Vector2(Raylib.GetScreenWidth() / 2.0f, Raylib.GetScreenHeight() / 2.0f);

            // panning
            if (Raylib.IsMouseButtonPressed(MouseButton.Middle))
            {
                isDragging = true;
                dragStartMouseScreen = Raylib.GetMousePosition();
                dragStartTarget = targetPosition;
            }

            if (isDragging)
            {
                if (Raylib.IsMouseButtonDown(MouseButton.Middle))
                {
                    Vector2 currentMouseScreen = Raylib.GetMousePosition();
                    Vector2 screenDelta = currentMouseScreen - dragStartMouseScreen;
                    
                    targetPosition = dragStartTarget - (screenDelta / cam.Zoom);
                    cam.Target = targetPosition;
                }
                else
                {
                    isDragging = false;
                }
            }
            else
            {
                // arrow key panning
                float moveSpeed = 5.0f * PixelsPerMeter;
                if (Raylib.IsKeyDown(KeyboardKey.Right)) targetPosition.X += moveSpeed * frameTime;
                if (Raylib.IsKeyDown(KeyboardKey.Left)) targetPosition.X -= moveSpeed * frameTime;
                if (Raylib.IsKeyDown(KeyboardKey.Down)) targetPosition.Y += moveSpeed * frameTime;
                if (Raylib.IsKeyDown(KeyboardKey.Up)) targetPosition.Y -= moveSpeed * frameTime;
            }

            // recenter
            if (Raylib.IsKeyPressed(KeyboardKey.Space))
            {
                targetPosition = Vector2.Zero;
                targetZoom = 1.0f;
                isDragging = false;
                cam.Target = Vector2.Zero;
                cam.Zoom = 1.0f;
            }

            // zooming
            float wheel = Raylib.GetMouseWheelMove();
            if (wheel != 0.0f)
            {
                targetZoom *= MathF.Pow(1 + ZoomFactor, wheel);
                targetZoom = Math.Clamp(targetZoom, MinZoom, MaxZoom);
            }

            // lerp zoom
            if (MathF.Abs(cam.Zoom - targetZoom) > 0.0001f)
            {
                Vector2 mouseWorldBefore = Raylib.GetScreenToWorld2D(Raylib.GetMousePosition(), cam);

                cam.Zoom += (targetZoom - cam.Zoom) * ZoomLerpSpeed * frameTime;
                cam.Zoom = Math.Clamp(cam.Zoom, MinZoom, MaxZoom);

                Vector2 mouseWorldAfter = Raylib.GetScreenToWorld2D(Raylib.GetMousePosition(), cam);
                targetPosition += (mouseWorldBefore - mouseWorldAfter);
                cam.Target = targetPosition;

                if (isDragging)
                {
                    dragStartMouseScreen = Raylib.GetMousePosition();
                    dragStartTarget = targetPosition;
                }
            }
            else if (!isDragging)
            {
                cam.Target.X += (targetPosition.X - cam.Target.X) * MoveLerpSpeed * frameTime;
                cam.Target.Y += (targetPosition.Y - cam.Target.Y) * MoveLerpSpeed * frameTime;
            }

            RaylibCamera = cam;
        }

        public void DrawGrid()
        {
            float screenW = Raylib.GetScreenWidth();
            float screenH = Raylib.GetScreenHeight();

            float cellPixels = GridSpacing * PixelsPerMeter * RaylibCamera.Zoom;
            float subCellPixels = cellPixels / 5.0f;

            Vector2 originScreen = Raylib.GetWorldToScreen2D(Vector2.Zero, RaylibCamera);

            Color gridColor = MuiDarkColor.SurfaceVariant.ToColor();
            Color subGridColor = new Color((byte)gridColor.R, (byte)gridColor.G, (byte)gridColor.B, (byte)75);
            Color mainGridColor = new Color((byte)gridColor.R, (byte)gridColor.G, (byte)gridColor.B, (byte)150);

            // subgrid lines
            float startSubX = originScreen.X % subCellPixels;
            if (startSubX > 0) startSubX -= subCellPixels;
            for (float x = startSubX; x <= screenW; x += subCellPixels)
            {
                float relativeToOriginX = x - originScreen.X;
                int indexX = (int)Math.Round(relativeToOriginX / subCellPixels);
                if (indexX % 5 == 0) continue;

                int ix = (int)Math.Round(x);
                Raylib.DrawLineEx(new Vector2(ix, 0), new Vector2(ix, screenH), 2.0f, subGridColor);
            }

            float startSubY = originScreen.Y % subCellPixels;
            if (startSubY > 0) startSubY -= subCellPixels;
            for (float y = startSubY; y <= screenH; y += subCellPixels)
            {
                float relativeToOriginY = y - originScreen.Y;
                int indexY = (int)Math.Round(relativeToOriginY / subCellPixels);
                if (indexY % 5 == 0) continue;

                int iy = (int)Math.Round(y);
                Raylib.DrawLineEx(new Vector2(0, iy), new Vector2(screenW, iy), 2.0f, subGridColor);
            }

            // main grid lines
            float startMainX = originScreen.X % cellPixels;
            if (startMainX > 0) startMainX -= cellPixels;
            for (float x = startMainX; x <= screenW; x += cellPixels)
            {
                int ix = (int)Math.Round(x);
                Raylib.DrawLineEx(new Vector2(ix, 0), new Vector2(ix, screenH), 3.0f, mainGridColor);
            }

            float startMainY = originScreen.Y % cellPixels;
            if (startMainY > 0) startMainY -= cellPixels;
            for (float y = startMainY; y <= screenH; y += cellPixels)
            {
                int iy = (int)Math.Round(y);
                Raylib.DrawLineEx(new Vector2(0, iy), new Vector2(screenW, iy), 3.0f, mainGridColor);
            }
        }

        public void DrawHUD()
        {
            float screenH = Raylib.GetScreenHeight();
            string hudText = $"X: {Position.X:F2}m  Y: {Position.Y:F2}m  Zoom: {Zoom:F2}x";
            Program.DrawText(hudText, 20, (int)screenH - 40, 20, MuiDarkColor.TextPrimary.ToColor());
        }
    }
}