C＃应用程序外部的图形对象-可行吗？

Question

I have already asked here but the only answer was related to positioning. I would need to make an app which would produce an image always following the mouse, outside of the app. I know now how to hook mouse position, but I have no clue how to let the object (image) be on the top of other apps. Anyway I dont know if it is even possible in .NET. Thanks!

Answer 1

One of the best and easiest ways to accomplish such a thing is to have a topmost window, with no border and not showing in the taskbar. That would allow you to basically draw whatever you want wherever you want it.

using System.Windows.Forms;

Form overlay = new Form();
overlay.FormBorderStyle = FormBorderStyle.None;
overlay.ShowInTaskbar = false;
overlay.TopMost = true;

For bonus points, you could even apply the toolbar-property and revoke it's right to be activated. That will yield a form which does not behave like a window, but like fe a tooltip. For that you need to subclass the Form, like this:

public class PassiveForm : Form
{
    public PassiveForm()
    {
        InitializeComponent();
    }

    protected override CreateParams CreateParams
    {
        get
        {
            CreateParams parameter = base.CreateParams;
            parameter.ExStyle |= 0x80; // Apply toolbar-property
            parameter.ExStyle |= 0x8000000; // Revoke acitvation
            return parameter;
        }
    }

    protected override bool ShowWithoutActivation
    {
        get
        {
            return true;
        }
    }
}

Following the mouse around is a little bit harder, but pooling the mouse location should work well enough.

Answer 2

You might try Graphics.FromHdc(IntPtr.Zero) . In plain old GDI this allowed you to draw directly on the desktop on top of everything. I'm not sure though if this still works in .NET.

Added: That said, I'd still go for the trasparent-background-window approach mentioned in another answer. Drawing directly on desktop is waaaay too messy and error-prone.