Re: Adding fake cursors when resizing a window.

[Keith David Bershatsky]

Thank you, Eli, for helping me to understand that the issue arises because the 
scroll-bars are added/removed by calling window-system functions that are 
platform specific.

As to w32term.c, I tentatively resolved the issue in 
w32_set_vertical_scroll_bar by preventing MoveWindow from repainting the 
old/new scroll bar when enlarging the main window.  However, I only tested a 
2-window left/right split.  I see that the current version of w32term.c uses 
SetWindowPos instead of MoveWindow.  I have not yet done any testing with 
altering the last argument to SetWindowPos (i.e., uFlags) to see if it is 
possible to prevent painting the old scroll bar when enlarging the main window. 
 [Draft patch proof concept attached.]

As to nsterm.m, I tentatively resolved the issue in ns_set_vertical_scroll_bar 
by destroying the scroll bar and preventing repaint with an Apple function 
called removeFromSuperviewWithoutNeedingDisplay, and then creating a new scroll 
bar.  [Draft patch proof concept attached.]

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> Date: [03-10-2019 11:27:10] <10 Mar 2019 20:27:10 +0200>
> From: Eli Zaretskii <address@hidden>
> To: Keith David Bershatsky <address@hidden>
> CC: address@hidden,address@hidden
> Subject: Re: Adding fake cursors when resizing a window.
> 
> > Date:  Sun, 10 Mar 2019 11:04:03 -0700
> > From:  Keith David Bershatsky <address@hidden>
> > Cc:  address@hidden,Martin Rudalics <address@hidden>
> >
> > -  Although the scroll bar in the center is no longer visible because it 
> > was overwritten during update_window, Emacs tries to remove the center 
> > scroll bar anyway and that is what erases the fake cursors along the 
> > vertical strip in the center of the screen.
> >
> > -  At about the exact same time that the scroll bar in the center of the 
> > screen gets erased, the right scroll bar on the far right of the window is 
> > added.
> 
> Isn't this because the window-system removes the scroll bars?

2019_03_13__21_16_50_327.diff
Description: application/diff