ScreenCaptureApp/ScreenCaptureForm.cs

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

namespace ScreenCaptureApp
{
    public partial class ScreenCaptureForm : Form
    {
        private Point startPoint;
        private Point endPoint;
        private bool isSelecting = false;
        private Bitmap screenBitmap;
        private Rectangle selectedRegion;

        public Image CapturedImage { get; private set; }

        public ScreenCaptureForm()
        {
            InitializeComponent();
            InitializeCaptureForm();
        }

        private void InitializeCaptureForm()
        {
            this.FormBorderStyle = FormBorderStyle.None;
            this.WindowState = FormWindowState.Maximized;
            this.Opacity = 0.3;
            this.DoubleBuffered = true;
            this.Cursor = Cursors.Cross;
            this.KeyPreview = true;

            // Создаем скриншот всего экрана
            CaptureScreen();
        }

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

            using (Graphics 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;
        }

        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(); // Перерисовываем форму
            }
            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)
            {
                using (Pen pen = new Pen(Color.Red, 2))
                {
                    Rectangle rect = GetSelectionRectangle();
                    e.Graphics.DrawRectangle(pen, rect);

                    // Рисуем перекрестие для точного выбора
                    e.Graphics.DrawLine(pen, new Point(rect.X, rect.Y + rect.Height / 2),
                                         new Point(rect.X + rect.Width, rect.Y + rect.Height / 2));
                    e.Graphics.DrawLine(pen, 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;
            }

            // Вырезаем выбранную область
            CapturedImage = new Bitmap(selectedRegion.Width, selectedRegion.Height);

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

            this.DialogResult = DialogResult.OK;
            this.Close();
        }

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