g.Draw blinking a lot

Question

I'm using this function in a Timer:

IntPtr Handle = FindWindow(null, "Notepad");

if (radioButton1.Checked)
{
    using (Graphics g = Graphics.FromHwnd(Handle))
    {
        Pen PN = new Pen(pictureBox2.BackColor, (Convert.ToInt32(numericUpDown2.Value)));
        g.DrawLine(PN, 961, 520, 961, 560);
        g.DrawLine(PN, 985, 540, 935, 540);
        g.Dispose();
    }
}

But the draw is blinking alot even if i set the timer interval to 1

_even if i set the timer interval to 1_ Huh? Meaning _even if I run it as often as I can_ ??? (Interval is in ms !) — TaW, May 21 '19 at 12:06
For a slower blink rate set Interval to larger value. 1000 is one second. - Also don't dispose what is created in a using clause! — TaW, May 21 '19 at 12:33
@TaW Slower interval is actually even worse It's not even drawing it properly — sdhp442, May 21 '19 at 12:40
Not sure if your approach will work. [See here](https://stackoverflow.com/questions/815667/how-to-draw-graphics-text-on-top-of-another-application) — TaW, May 21 '19 at 12:58
What is that you actually want to do here? I doubt you just want to paint a cross in a fixed position over Notepad's client area. — Jimi, May 21 '19 at 13:11

score -1 · Answer 1 · answered May 21 '19 at 15:56

Your code will only get the main window's handle.

Most applications have other controls that cover that clientarea.

Instead of drawing onto the clientarea you need to get the the handle of Notepad's textarea.

You can test this by

testing the handle value. If it is 0 you only got the desktop. This probably what you have been seeing.
If you test it with a form of your own it will show your cross if and only if the drawing area is not covered by other controls..

It is also a good idea to enumerate the processes to get at the correct titles. Here is an example I found in another post:

public static IntPtr WinGetHandle(string wName)
{
    IntPtr hWnd = IntPtr.Zero;
    foreach (Process pList in Process.GetProcesses())
    {
        if (pList.MainWindowTitle.Contains(wName))
        {
            hWnd = pList.MainWindowHandle;
        }
        Console.WriteLine(pList.MainWindowTitle);
    }
    return hWnd;
}

It will take some more trial and error code to find a suitable subhandle of the application's surface..

Still can't figure out how to fix the blinking draw it's working better when i use "for ( ; ; )", but if i use that i can't go back to the form anymore — sdhp442, May 21 '19 at 17:19
What rate do you aim to get? Also: Are you claiming that your code actually draws onto Notepad?? (Test: Move Notepade around; will it still get the cross at the same spot??) — TaW, May 21 '19 at 18:01

g.Draw blinking a lot

1 Answers1