Aula de Wanfranklin

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Pintar
{
    enum Ferramentas
        {
                caneta, baldeDeTinta
        }
    public partial class FrmPrincipal : Form
    {
        private Ferramentas ferramentas = Ferramentas.caneta;
        private Color colorA = Color.Black;
        private int prevX;
        private int prevY;
        private bool canDesenhar = false;
        private bool canUsarBarraFerramentas = true;
        private Thread thread = null;

        public FrmPrincipal()
        {
            InitializeComponent();
            pbTinta.Image = CriarBmpVazio(Color.White, panel1.Width, panel1.Height);
            pbDesenho.Image = CriarBmpVazio(colorA, pbDesenho.Width, pbDesenho.Height);
            timer1.Start();
        }

        private void UIThread(MethodInvoker codigo) {
            if (this.InvokeRequired)
            {
                this.Invoke(codigo);
            }
            else {
                codigo.Invoke();
            }
        }
        private Bitmap CriarBmpVazio(Color c, int width, int height) {
            Bitmap bmp = new Bitmap(width, height);

            using (var g = Graphics.FromImage(bmp)) {
                g.Clear(c);
            }

            return bmp;
        }

        private Bitmap Caneta(Bitmap bmp, MouseEventArgs e) {
            using (var caneta = new Pen(colorA, 1)) {
                using (var g = Graphics.FromImage(bmp)) {
                    g.DrawLine(caneta, prevX, prevY, e.X, e.Y);
                }
            }

            return bmp;
        }

        private Bitmap BaldeDeTinta(Bitmap bmp, Color pC, Point point)
        {
            Stack<Point> stack = new Stack<Point>();
            stack.Push(point);

            while (stack.Count > 0)
            {
                Point p = stack.Pop();

                if (p.X >= 0 && p.X < bmp.Width && p.Y >= 0 && p.Y < bmp.Height)
                {
                    if (bmp.GetPixel(p.X, p.Y) != pC)
                        continue;

                    bmp.SetPixel(p.X, p.Y, colorA);
                    stack.Push(new Point(p.X + 1, p.Y));
                    stack.Push(new Point(p.X - 1, p.Y));
                    stack.Push(new Point(p.X, p.Y + 1));
                    stack.Push(new Point(p.X, p.Y - 1));
                }
            }
            return bmp;
        }

        private void pbDesenho_MouseDown(object sender, MouseEventArgs e)
        {
            prevX = e.X;
            prevY = e.Y;
            canDesenhar = true;

            switch (ferramentas) {
                case Ferramentas.baldeDeTinta:
                    thread = new Thread(() => {
                        UIThread(delegate { flowLayoutPanel1.Enabled = false; });
                        Bitmap b = pbDesenho.Image as Bitmap;
                        Color c = b.GetPixel(e.X, e.Y);

                        UIThread(delegate {
                            pbDesenho.Image = BaldeDeTinta(b, c, new Point(e.X, e.Y));
                            flowLayoutPanel1.Enabled = true;
                        });
                    });

                    thread.Start();
                break;
            }
        }
    }
}