ScreenCaptureApp/ScreenCaptureForm.cs

using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.Windows.Forms;

namespace ScreenCaptureApp
{
    public sealed class ScreenCaptureForm : Form
    {
        private Point _startPoint;
        private Point _endPoint;
        private bool _isSelecting;
        private Bitmap _screenBitmap;
        private Rectangle _selectedRegion;
        private Pen _selectionPen;

        public Bitmap CapturedImage { get; private set; }

        public ScreenCaptureForm()
        {
            InitializeForm();
            CaptureScreen();
        }

        private void InitializeForm()
        {
            this.FormBorderStyle = FormBorderStyle.None;
            this.WindowState = FormWindowState.Maximized;
            this.Opacity = 0.3;
            this.DoubleBuffered = true;
            this.Cursor = Cursors.Cross;
            this.KeyPreview = true;
            this.StartPosition = FormStartPosition.Manual;
            this.Location = Point.Empty;
            this.Size = Screen.PrimaryScreen.Bounds.Size;

            _selectionPen = new Pen(Color.Red, 2) { DashStyle = System.Drawing.Drawing2D.DashStyle.Dash };
        }

        private void CaptureScreen()
        {
            try
            {
                _screenBitmap = new Bitmap(
                    Screen.PrimaryScreen.Bounds.Width,
                    Screen.PrimaryScreen.Bounds.Height,
                    PixelFormat.Format32bppArgb);

                using (var g = Graphics.FromImage(_screenBitmap))
                {
                    g.CopyFromScreen(
                        Screen.PrimaryScreen.Bounds.X,
                        Screen.PrimaryScreen.Bounds.Y,
                        0, 0,
                        Screen.PrimaryScreen.Bounds.Size,
                        CopyPixelOperation.SourceCopy);
                }

                this.BackgroundImage = _screenBitmap;
            }
            catch
            {
                _screenBitmap?.Dispose();
                throw;
            }
        }

        protected override void OnMouseDown(MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Left)
            {
                _startPoint = e.Location;
                _isSelecting = true;
            }
            base.OnMouseDown(e);
        }

        protected override void OnMouseMove(MouseEventArgs e)
        {
            if (_isSelecting)
            {
                _endPoint = e.Location;
                this.Invalidate();
            }
            base.OnMouseMove(e);
        }

        protected override void OnMouseUp(MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Left && _isSelecting)
            {
                _endPoint = e.Location;
                _isSelecting = false;
                CaptureSelectedRegion();
            }
            base.OnMouseUp(e);
        }

        protected override void OnPaint(PaintEventArgs e)
        {
            if (_isSelecting)
            {
                var rect = GetSelectionRectangle();
                e.Graphics.DrawRectangle(_selectionPen, rect);

                // Перекрестие для точного выбора
                e.Graphics.DrawLine(_selectionPen,
                    new Point(rect.X, rect.Y + rect.Height / 2),
                    new Point(rect.X + rect.Width, rect.Y + rect.Height / 2));
                e.Graphics.DrawLine(_selectionPen,
                    new Point(rect.X + rect.Width / 2, rect.Y),
                    new Point(rect.X + rect.Width / 2, rect.Y + rect.Height));
            }
            base.OnPaint(e);
        }

        private Rectangle GetSelectionRectangle()
        {
            return new Rectangle(
                Math.Min(_startPoint.X, _endPoint.X),
                Math.Min(_startPoint.Y, _endPoint.Y),
                Math.Abs(_startPoint.X - _endPoint.X),
                Math.Abs(_startPoint.Y - _endPoint.Y));
        }

        private void CaptureSelectedRegion()
        {
            _selectedRegion = GetSelectionRectangle();

            if (_selectedRegion.Width <= 0 || _selectedRegion.Height <= 0)
            {
                this.DialogResult = DialogResult.Cancel;
                return;
            }

            try
            {
                CapturedImage = new Bitmap(_selectedRegion.Width, _selectedRegion.Height);

                using (var g = Graphics.FromImage(CapturedImage))
                {
                    g.DrawImage(_screenBitmap,
                        new Rectangle(0, 0, _selectedRegion.Width, _selectedRegion.Height),
                        _selectedRegion,
                        GraphicsUnit.Pixel);
                }

                this.DialogResult = DialogResult.OK;
            }
            catch
            {
                CapturedImage?.Dispose();
                this.DialogResult = DialogResult.Cancel;
            }
            finally
            {
                this.Close();
            }
        }

        protected override void OnKeyDown(KeyEventArgs e)
        {
            if (e.KeyCode == Keys.Escape)
            {
                this.DialogResult = DialogResult.Cancel;
                this.Close();
            }
            base.OnKeyDown(e);
        }

        protected override void Dispose(bool disposing)
        {
            if (disposing)
            {
                _screenBitmap?.Dispose();
                _selectionPen?.Dispose();
                CapturedImage?.Dispose();
            }
            base.Dispose(disposing);
        }
    }
}