ScienceLab.FrictionForce/Assets/Scripts/ChalkDrawer.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class ChalkDrawer : MonoBehaviour
{
    [SerializeField] private Camera _camera;
    [SerializeField] private RenderTexture _boardTexture;
    [SerializeField] private float _brushSize = 0.02f;
    [SerializeField] private float _eraserSize = 0.05f;
    [SerializeField] private Color _chalkColor = Color.white;
    [SerializeField] private float _holdDistance = 1.5f;
    [SerializeField] private float _followSpeed = 12f;

    public bool IsHoldingChalk => _holdingChalk;

    private bool _holdingChalk = false;
    private bool _isErasing = false;
    private GameObject _chalkObject = null;
    private Rigidbody _chalkRb = null;
    private Collider _chalkCollider = null;
    private Texture2D _drawTexture;
    private bool _textureReady = false;
    private Vector3 _originalPosition;

    private void Start()
    {
        InitTexture();
    }

    private void InitTexture()
    {
        if (_boardTexture == null) return;

        _drawTexture = new Texture2D(_boardTexture.width, _boardTexture.height, TextureFormat.RGBA32, false);

        Color[] pixels = new Color[_boardTexture.width * _boardTexture.height];
        for (int i = 0; i < pixels.Length; i++)
            pixels[i] = Color.black;
        _drawTexture.SetPixels(pixels);
        _drawTexture.Apply();

        Graphics.Blit(_drawTexture, _boardTexture);

        GameObject board = GameObject.FindGameObjectWithTag("Board");
        if (board != null)
        {
            MeshRenderer boardRenderer = board.GetComponent<MeshRenderer>();
            if (boardRenderer != null)
                boardRenderer.material.mainTexture = _boardTexture;
        }

        _textureReady = true;
    }

    private void Update()
    {
        if (!_holdingChalk) return;

        HandleHolding();
        HandleDrawing();

        if (Input.GetMouseButtonDown(1))
            DropChalk();
    }

    public void PickupChalk(GameObject chalk)
    {
        _originalPosition = chalk.transform.position;
        _chalkObject = chalk;
        _chalkRb = chalk.GetComponent<Rigidbody>();
        _chalkCollider = chalk.GetComponent<Collider>();

        if (_chalkRb != null)
        {
            _chalkRb.useGravity = false;
            _chalkRb.velocity = Vector3.zero;
            _chalkRb.angularVelocity = Vector3.zero;
        }

        if (_chalkCollider != null)
            _chalkCollider.enabled = false;

        _isErasing = false;
        _holdingChalk = true;
    }

    public void PickupTowel(GameObject towel)
    {
        _originalPosition = towel.transform.position;
        _chalkObject = towel;
        _chalkRb = towel.GetComponent<Rigidbody>();
        _chalkCollider = towel.GetComponent<Collider>();

        if (_chalkRb != null)
        {
            _chalkRb.useGravity = false;
            _chalkRb.velocity = Vector3.zero;
            _chalkRb.angularVelocity = Vector3.zero;
        }

        if (_chalkCollider != null)
            _chalkCollider.enabled = false;

        _isErasing = true;
        _holdingChalk = true;
    }

    private void HandleHolding()
    {
        if (_chalkObject == null) return;

        Ray ray = _camera.ScreenPointToRay(Input.mousePosition);
        Vector3 targetPos = ray.origin + ray.direction * _holdDistance;

        _chalkObject.transform.position = Vector3.Lerp(
            _chalkObject.transform.position,
            targetPos,
            Time.deltaTime * _followSpeed
        );
    }

    private void HandleDrawing()
    {
        if (!_textureReady) return;

        if (Input.GetMouseButton(0))
        {
            Ray ray = _camera.ScreenPointToRay(Input.mousePosition);
            if (Physics.Raycast(ray, out RaycastHit hit))
            {
                if (hit.collider.CompareTag("Board"))
                    DrawOnTexture(hit.textureCoord);
            }
        }
    }

    private void DrawOnTexture(Vector2 uv)
    {
        Color paintColor = _isErasing ? Color.black : _chalkColor;
        float size = _isErasing ? _eraserSize : _brushSize;

        int x = (int)(uv.x * _drawTexture.width);
        int y = (int)(uv.y * _drawTexture.height);
        int radius = Mathf.Max(1, (int)(size * _drawTexture.width));

        for (int i = -radius; i <= radius; i++)
        {
            for (int j = -radius; j <= radius; j++)
            {
                if (i * i + j * j <= radius * radius)
                {
                    int px = Mathf.Clamp(x + i, 0, _drawTexture.width - 1);
                    int py = Mathf.Clamp(y + j, 0, _drawTexture.height - 1);
                    _drawTexture.SetPixel(px, py, paintColor);
                }
            }
        }

        _drawTexture.Apply();
        Graphics.Blit(_drawTexture, _boardTexture);
    }

    private void DropChalk()
    {
        if (_chalkObject == null) return;

        if (_chalkRb != null)
        {
            _chalkRb.useGravity = false;
            _chalkRb.velocity = Vector3.zero;
            _chalkRb.angularVelocity = Vector3.zero;
        }

        _chalkObject.transform.position = _originalPosition;

        if (_chalkRb != null)
        {
            _chalkRb.useGravity = true;
            _chalkRb.WakeUp();
        }

        if (_chalkCollider != null)
            _chalkCollider.enabled = true;

        _holdingChalk = false;
        _isErasing = false;
        _chalkObject = null;
        _chalkRb = null;
        _chalkCollider = null;
    }
}