Winforms: A draggable transparent rectangle

Question

Morning,

I\'m just about ready to claw my own eyes out at this point. I\'m building a basic image editor using Windows forms on .NET 3.5, and what I need is a \'sele

Answer 1

You should be able to after reading this Painting On Top Of Child Controls

I have used ControlPaint.DrawReversibleFrame(_FrameRect, Color.Black, FrameStyle.Dashed); myself before and it works fine :)

Answer 2

You would be better off to make a custom control which draws an image, and overlays the rectangle on top. Then, you could handle mouse events to 'move' the rectangle.

Some pseudocode to get you started:

class cropcontrol

onpaint
  paint image
  paint rectangle using rect location

onmousemove
  if mouse down
    update rect location

Answer 3

I actualy made an aplication for screen capturing that worked the way you describe, to make it draggable i use Mouse events. To make it transparent i simply made another Form control with semi-transparent png Image as background image.

public partial class Photo : Form
    {
        public delegate void ScreenShotReadyDelegate(Bitmap g);
        public event ScreenShotReadyDelegate ScreenShotReady;

        bool Moving = false;
        Point oldLoc = new Point();

        public Photo()
        {
            InitializeComponent();
            this.FormBorderStyle = FormBorderStyle.None;
            this.DoubleBuffered = true;
            this.SetStyle(ControlStyles.ResizeRedraw, true);
        } 

        private void Photo_MouseDoubleClick(object sender, MouseEventArgs e)
        {
            this.BackgroundImage = null;
            this.Invalidate();
            Rectangle bounds = this.Bounds;
            using (Bitmap bitmap = new Bitmap(bounds.Width, bounds.Height))
            {
                using (Graphics g = Graphics.FromImage(bitmap))
                {
                    g.CopyFromScreen(new Point(bounds.Left, bounds.Top), Point.Empty, bounds.Size);
                }
                ScreenShotReady(bitmap);
            }
            this.BackgroundImage = Properties.Resources.rect;
            this.Invalidate();
        }

        private void Photo_MouseDown(object sender, MouseEventArgs e)
        {
            this.Moving = true;
            this.oldLoc = MousePosition;
        }

        private void Photo_MouseMove(object sender, MouseEventArgs e)
        {
            if (this.Moving)
            {
                Point vector = new Point(MousePosition.X - this.oldLoc.X, MousePosition.Y - this.oldLoc.Y);
                this.Location = new Point(this.Location.X + vector.X, this.Location.Y + vector.Y);
                this.oldLoc = MousePosition;
            }
        }

        private void Photo_MouseUp(object sender, MouseEventArgs e)
        {
            this.Moving = false;
        }
    }