hiimray-co-uk-www-posts/2020/11/BorderlessForm.cs

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

namespace WindowsFormsApp2
{
    public class BorderlessForm : Form
    {
        protected bool isDragging = false;
        protected Rectangle lastRectangle = new Rectangle();


        public BorderlessForm() : base()
        {
            this.FormBorderStyle = FormBorderStyle.None;

            initialiseFormEdge();
        }


        protected void initialiseFormEdge()
        {
            int resizeWidth = 5;

            this.MouseDown += new MouseEventHandler(form_MouseDown);
            this.MouseMove += new MouseEventHandler(form_MouseMove);
            this.MouseUp += delegate (object sender, MouseEventArgs e)
            {
                isDragging = false;
            };

            // bottom
            UserControl uc1 = new UserControl()
            {
                Anchor = (AnchorStyles.Left | AnchorStyles.Bottom | AnchorStyles.Right),
                Height = resizeWidth,
                Width = this.DisplayRectangle.Width - (resizeWidth * 2),
                Left = resizeWidth,
                Top = this.DisplayRectangle.Height - resizeWidth,
                BackColor = Color.Transparent,
                Cursor = Cursors.SizeNS
            };
            uc1.MouseDown += form_MouseDown;
            uc1.MouseUp += form_MouseUp;
            uc1.MouseMove += delegate (object sender, MouseEventArgs e)
            {
                if (isDragging)
                {
                    this.Size = new Size(lastRectangle.Width, e.Y - lastRectangle.Y + this.Height);
                }
            };
            uc1.BringToFront();

            this.Controls.Add(uc1);

            // right
            UserControl uc2 = new UserControl()
            {
                Anchor = (AnchorStyles.Top | AnchorStyles.Right | AnchorStyles.Bottom),
                Height = this.DisplayRectangle.Height - (resizeWidth * 2),
                Width = resizeWidth,
                Left = this.DisplayRectangle.Width - resizeWidth,
                Top = resizeWidth,
                BackColor = Color.Transparent,
                Cursor = Cursors.SizeWE
            };
            uc2.MouseDown += form_MouseDown;
            uc2.MouseUp += form_MouseUp;
            uc2.MouseMove += delegate (object sender, MouseEventArgs e)
            {
                if (isDragging)
                {
                    this.Size = new Size(e.X - lastRectangle.X + this.Width, lastRectangle.Height);
                }
            };
            uc2.BringToFront();

            this.Controls.Add(uc2);

            // bottom-right
            UserControl uc3 = new UserControl()
            {
                Anchor = (AnchorStyles.Bottom | AnchorStyles.Right),
                Height = resizeWidth,
                Width = resizeWidth,
                Left = this.DisplayRectangle.Width - resizeWidth,
                Top = this.DisplayRectangle.Height - resizeWidth,
                BackColor = Color.Transparent,
                Cursor = Cursors.SizeNWSE
            };
            uc3.MouseDown += form_MouseDown;
            uc3.MouseUp += form_MouseUp;
            uc3.MouseMove += delegate (object sender, MouseEventArgs e)
            {
                if (isDragging)
                {
                    this.Size = new Size((e.X - lastRectangle.X + this.Width), (e.Y - lastRectangle.Y + this.Height));
                }
            };
            uc3.BringToFront();

            this.Controls.Add(uc3);

            // top-right
            UserControl uc4 = new UserControl()
            {
                Anchor = (AnchorStyles.Top | AnchorStyles.Right),
                Height = resizeWidth,
                Width = resizeWidth,
                Left = this.DisplayRectangle.Width - resizeWidth,
                Top = 0,
                BackColor = Color.Transparent,
                Cursor = Cursors.SizeNESW
            };
            uc4.MouseDown += form_MouseDown;
            uc4.MouseUp += form_MouseUp;
            uc4.MouseMove += delegate (object sender, MouseEventArgs e)
            {
                if (isDragging)
                {
                    int diff = (e.Location.Y - lastRectangle.Y);
                    int y = (this.Location.Y + diff);

                    this.Location = new Point(this.Location.X, y);
                    this.Size = new Size(e.X - lastRectangle.X + this.Width, (this.Height + (diff * -1)));
                }
            };
            uc4.BringToFront();
            //uc4.BackColor = Color.Firebrick;

            this.Controls.Add(uc4);

            // top
            UserControl uc5 = new UserControl()
            {
                Anchor = (AnchorStyles.Top | AnchorStyles.Left | AnchorStyles.Right),
                Height = resizeWidth,
                Width = this.DisplayRectangle.Width - (resizeWidth * 2),
                Left = resizeWidth,
                Top = 0,
                BackColor = Color.Transparent,
                Cursor = Cursors.SizeNS
            };
            uc5.MouseDown += form_MouseDown;
            uc5.MouseUp += form_MouseUp;
            uc5.MouseMove += delegate (object sender, MouseEventArgs e)
            {
                if (isDragging)
                {
                    int diff = (e.Location.Y - lastRectangle.Y);
                    int y = (this.Location.Y + diff);

                    this.Location = new Point(this.Location.X, y);
                    this.Size = new Size(lastRectangle.Width, (this.Height + (diff * -1)));
                }
            };
            uc5.BringToFront();

            this.Controls.Add(uc5);

            // left
            UserControl uc6 = new UserControl()
            {
                Anchor = (AnchorStyles.Top | AnchorStyles.Left | AnchorStyles.Bottom),
                Height = this.DisplayRectangle.Height - (resizeWidth * 2),
                Width = resizeWidth,
                Left = 0,
                Top = resizeWidth,
                BackColor = Color.Transparent,
                Cursor = Cursors.SizeWE
            };
            uc6.MouseDown += form_MouseDown;
            uc6.MouseUp += form_MouseUp;
            uc6.MouseMove += delegate (object sender, MouseEventArgs e)
            {
                if (isDragging)
                {
                    int diff = (e.Location.X - lastRectangle.X);
                    int x = (this.Location.X + diff);

                    this.Location = new Point(x, this.Location.Y);
                    this.Size = new Size((this.Width + (diff * -1)), this.Height);
                }
            };
            uc6.BringToFront();

            this.Controls.Add(uc6);

            // bottom-left
            UserControl uc7 = new UserControl()
            {
                Anchor = (AnchorStyles.Bottom | AnchorStyles.Left),
                Height = resizeWidth,
                Width = resizeWidth,
                Left = 0,
                Top = this.DisplayRectangle.Height - resizeWidth,
                BackColor = Color.Transparent,
                Cursor = Cursors.SizeNESW
            };
            uc7.MouseDown += form_MouseDown;
            uc7.MouseUp += form_MouseUp;
            uc7.MouseMove += delegate (object sender, MouseEventArgs e)
            {
                if (isDragging)
                {
                    int diff = (e.Location.X - lastRectangle.X);
                    int x = (this.Location.X + diff);

                    this.Location = new Point(x, this.Location.Y);
                    this.Size = new Size((this.Width + (diff * -1)), (e.Y - lastRectangle.Y + this.Height));
                }
            };
            uc7.BringToFront();

            this.Controls.Add(uc7);

            // bottom-left
            UserControl uc8 = new UserControl()
            {
                Anchor = (AnchorStyles.Top | AnchorStyles.Left),
                Height = resizeWidth,
                Width = resizeWidth,
                Left = 0,
                Top = 0,
                BackColor = Color.Transparent,
                Cursor = Cursors.SizeNWSE
            };
            uc8.MouseDown += form_MouseDown;
            uc8.MouseUp += form_MouseUp;
            uc8.MouseMove += delegate (object sender, MouseEventArgs e)
            {
                if (isDragging)
                {
                    int dX = (e.Location.X - lastRectangle.X);
                    int dY = (e.Location.Y - lastRectangle.Y);
                    int x = (this.Location.X + dX);
                    int y = (this.Location.Y + dY);

                    this.Location = new Point(x, y);
                    this.Size = new Size((this.Width + (dX * -1)), (this.Height + (dY * -1)));
                }
            };
            uc8.BringToFront();

            this.Controls.Add(uc8);
        }


        private void form_MouseDown(object sender, MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Left)
            {
                isDragging = true;
                lastRectangle = new Rectangle(e.Location.X, e.Location.Y, this.Width, this.Height);
            }
        }

        private void form_MouseMove(object sender, MouseEventArgs e)
        {
            if (isDragging)
            {
                int x = (this.Location.X + (e.Location.X - lastRectangle.X));
                int y = (this.Location.Y + (e.Location.Y - lastRectangle.Y));

                this.Location = new Point(x, y);
            }
        }

        private void form_MouseUp(object sender, MouseEventArgs e)
        {
            isDragging = false;
        }

    }
}