using System using System Collections Generic using System ComponentMo

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

namespace Graphics_lab_2_dop
{
    public partial class FormBackgroundScreen : Form
    {
        Rectangle rectSelected; //прямоугольник которым выделяют
        Rectangle rectBack; //прямоугольник для заливки всего окна
        Size size;
        Point clickPoint;
        Point nowPoint;
        Graphics gr;
        BufferedGraphics bufferGraphics;
        BufferedGraphicsContext bufferGraphicsContext;
        SolidBrush brushBack; //кисти
        Pen pen;
        Brush brushInRect;

        public FormBackgroundScreen()
        {
            //InitializeComponent();

            MouseDown += new MouseEventHandler(FormBackgroundScreen_MouseDown);
            MouseMove += new MouseEventHandler(FormBackgroundScreen_MouseMove);
            MouseUp += new MouseEventHandler(FormBackgroundScreen_MouseUp);

            size = new Size(0, 0);
            clickPoint = new Point(0, 0);
            nowPoint = new Point(0, 0);
            rectSelected = new Rectangle(nowPoint, size);
            //окрашенное окно стало прозрачным внутри прямоугольника
            brushBack = new SolidBrush(Color.Beige);    
            brushInRect = new SolidBrush(Color.BlanchedAlmond);
            pen = new Pen(Color.DeepSkyBlue, 1); //то чем рисуется выделяемая область
            rectBack = Screen.PrimaryScreen.Bounds;
            this.BackColor = brushBack.Color;

            this.SetStyle(ControlStyles.OptimizedDoubleBuffer | ControlStyles.SupportsTransparentBackColor, true);
            this.UpdateStyles();

            gr = Graphics.FromHwnd(this.Handle);
            bufferGraphicsContext = BufferedGraphicsManager.Current;
        }

        /// <summary>Отрисовываем всё в буфере </summary>
        public void DrawToBuffer()
        {   //выставляем размер буфера
            bufferGraphicsContext.MaximumBuffer = new Size(this.Width, this.Height);

            bufferGraphics = bufferGraphicsContext.Allocate(gr,
                 new Rectangle(0, 0, this.Width, this.Height)); //создаём буфер

            bufferGraphics.Graphics.FillRectangle(brushBack, ClientRectangle);
            //начинаем это делать именно здесь, потому-что нужно сдвигать только рамку
            rectSelected = new Rectangle(rectSelected.X - 1, rectSelected.Y - 1, rectSelected.Width + 1, rectSelected.Height + 1);

            bufferGraphics.Graphics.DrawRectangle(pen, rectSelected); //рисуем новый прямоугольник

            //возвращаем всё на место как было
            rectSelected = new Rectangle(rectSelected.X + 1, rectSelected.Y + 1, rectSelected.Width - 1, rectSelected.Height - 1);

            bufferGraphics.Graphics.FillRectangle(brushInRect, rectSelected); //закрашиваем внутреннюю часть выделения

            bufferGraphics.Render(); //выводим, то что отрисовалось в буфере
        }

        private void FormBackgroundScreen_MouseDown(object sender, MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Left) //если нажата левая кнопка мыши
            {
                clickPoint.X = e.Location.X;
                clickPoint.Y = e.Location.Y;
            }
        }
        int PY = 0, PX = 0;
        int LY = 0, LX = 0;
        private void FormBackgroundScreen_MouseMove(object sender, MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Left)
            {
                nowPoint.X = e.X;
                PX = e.X;
                nowPoint.Y = e.Y;
                PY = e.Y;
                if (nowPoint.X > clickPoint.X)
                {
                    size.Width = nowPoint.X - clickPoint.X; //вычитаем текущее место из места где был первый клик 
                    rectSelected.X = clickPoint.X;
                }
                else
                {
                    size.Width = clickPoint.X - nowPoint.X;
                    rectSelected.X = clickPoint.X - size.Width;
                }

                if (nowPoint.Y > clickPoint.Y)
                {
                    size.Height = nowPoint.Y - clickPoint.Y;
                    rectSelected.Y = clickPoint.Y;
                }
                else
                {
                    size.Height = clickPoint.Y - nowPoint.Y;
                    rectSelected.Y = clickPoint.Y - size.Height;
                }

                rectSelected.Width = size.Width;
                rectSelected.Height = size.Height;

                DrawToBuffer(); //Производим отрисовку в буфере
            }
        }

        private void FormBackgroundScreen_MouseUp(object sender, MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Left)
            {
                LX = e.X;
                LY = e.Y;
                int xCoord = (PX - LX) / 2;
                int yCoord = (PY - LY) / 2;
                int a = PX - LX;
                int b = PY - LY;
                Circul(xCoord, yCoord, a, b);
            }
        }
        private void Circul(int x, int y, int a, int b)
        {
            int col = 0, row = 0;
            int a_square, b_square, two_a_square, two_b_square, four_a_square, four_b_square, d;
            Graphics g = Graphics.FromHwnd(this.Handle);
            Pen Brush = new Pen(new SolidBrush(Color.Blue), 2f);
            b_square = b * b;
            a_square = a * a;
            row = b;
            col = 0;
            two_a_square = a_square << 1;
            four_a_square = a_square << 2;
            four_b_square = b_square << 2;
            two_b_square = b_square << 1;
            d = two_a_square * ((row - 1) * (row)) + a_square + two_b_square * (1 - a_square);
            while (a_square * (row) > b_square * (col))
            {
                g.DrawRectangle(Brush, col + x, row + y, 1, 1);
                g.DrawRectangle(Brush, col + x, y - row, 1, 1);
                g.DrawRectangle(Brush, x - col, row + y, 1, 1);
                g.DrawRectangle(Brush, x - col, y - row, 1, 1);
                if (d >= 0)
                {
                    row--;
                    d -= four_a_square * (row);
                }
                d += two_b_square * (3 + (col << 1));
                col++;
            }
            d = two_b_square * (col + 1) * col + two_a_square * (row * (row - 2) + 1) + (1 - two_a_square) * b_square;
            while (((row) + 1) > 0)
            {
                g.DrawRectangle(Brush, col + x, row + y, 1, 1);
                g.DrawRectangle(Brush, col + x, y - row, 1, 1);
                g.DrawRectangle(Brush, x - col, row + y, 1, 1);
                g.DrawRectangle(Brush, x - col, y - row, 1, 1);
                if (d <= 0)
                {
                    col++;
                    d += four_b_square * col;
                }
                row--;
                d += two_a_square * (3 - (row << 1));
            }
        }
    }

}