[Lazarus] How to hide pop-up menu before taking a screen snapshot?

[Denis Kozlov]

Hi,

I had a similar experience with taking a screenshot programmatically. 
Simply waiting or processing application messages after hiding the form 
often doesn't help, and results in a form being a part of the screenshot 
anyway.

I managed to work around it by forcing Windows to repaint everything on 
the desktop by broadcasting WM_PAINT message, like so:

SendMessageTimeout(HWND_BROADCAST, WM_PAINT, 0, 0, SMTO_ABORTIFHUNG, 
1000, MsgResult);

You might also need to disable transition effects (fade-in and fade-out) 
by setting the DWMWA_TRANSITIONS_FORCEDISABLED flag on the form before 
hiding it, and then unsetting it when showing the form again.

DwmSetWindowAttribute(AForm.Handle, DWMWA_TRANSITIONS_FORCEDISABLED, 
@dwAttribute, SizeOf(dwAttribute));

Good luck,
Denis


On 07/02/2021 09:37, Bo Berglund via lazarus wrote:
> I have worked on a tool to copy a region of the Windows desktop for use in
> illustrations. The tool consists of a transparent form which is supposed to be
> located on top of the area to copy.
>
> This form has a pop-up menu where there are 3 items to select from:
> - Copy image
> - Copy position
> - Close
>
> When I use the "Copy image" function the resulting image contains the selected
> menu item caption on top of the copied desktop bitmap...
>
> I have tried various ways to get rid of this but everything I tried has failed.
> So how can I hide the menu item caption in code before I make the image
> extraction?
>
> I even added a timer set to 50 ms interval and put the image copy in its ontimer
> event hoping that the menu click should have exited and the text disappeared
> before the image copy happened, but no go...
>
> Here is the way the copy is commanded via the popup menu:
> http://blog.boberglund.com/files/Lazarus_popmenu_usage.png
>
> And here is a captured image where the popup caption is visible:
> http://blog.boberglund.com/files/Lazarus_popmenu.png
>
> As you can see the caption of the clicked menu item is still present in the
> screenshot image...
>
> Here is parts of the code:
>
> procedure TfrmMain.miCopyImageClick(Sender : TObject);
> begin
>    //CopyScreenRect;  //Moved to timer
>    //miCopyImage.Visible := false; //Does not work
>    //self.Refresh;  //Does not work
>    timCopyImg.Enabled := true;  //make copy inside timer event?
> end;
>
> procedure TfrmMain.miCopyPosClick(Sender : TObject);
> begin
>    SaveRectCoords; //Saving rect coordinates to clipboard (OK)
> end;
>
> procedure TfrmMain.timCopyImgTimer(Sender : TObject);
> begin
>    timCopyImg.Enabled := false;
>    miCopyImage.Visible := false; //Does not work, caption still present
>    self.Refresh;  //Does also not work to remove caption
>    CopyScreenRect;
>    miCopyImage.Visible := true;  //Put it back to enable next capture
> end;
>
> procedure TfrmMain.CopyScreenRect;
> var
>    MyCapture : TBgraBitmap;
>    Clip: TRect;
> begin
>    try
>      Clip := Bounds(Self.Left, Self.Top, Self.Width, Self.Height);
>      Self.Visible := false; //Hide selection form before copy
>      //Self.Hide;  //Not working for popup menu item...
>      MyCapture := TBgraBitmap.Create();
>      MyCapture.TakeScreenShot(Clip);
>      Self.Visible := true; //Show selection form after copy is done
>      //Self.Show;  //Not working for popup menu item...
>      Clipboard.Assign(MyCapture.Bitmap);
>    except
>      on E: exception do
>        Clipboard.AsText := E.Message;
>    end;
> end;
>
> Even Self.Visible or Self.Hide do not remove the menuitem caption....
>
> What can I do?
>
> Lazarus 2.0.10 / fpc 3.2.0 on Windows 10
>
>