Re: Can someone explain this code in xterm.c?

[Richard Stallman <rms@gnu.org>]

    In x_set_window_size_1, the vertical_scroll_bar_extra setting may be
    set to a non-integral fraction of the canonical column width of the
    frame:

It appears to me that vertical_scroll_bar_extra holds the 
width in pixels of the scroll bar, in all cases.  Its name is
misleading.

You would think that FRAME_SCROLL_BAR_PIXEL_WIDTH has that value,
but it is different.  It records the specified pixel width of the
scroll bar, or 0 if it has not been specified.

Perhaps both names should be changed.

    Anywhere else (including the normal X widget case, GTK, W32, and MAC
    ports), the vertical_scroll_bar_extra is set to an multiple of the
    canonical column width.

I think there are some other places where it uses
FRAME_SCROLL_BAR_PIXEL_WIDTH for this.

    This setting is used in the calculation of the total width of the
    frame window (in macro CHAR_TO_PIXEL_WIDTH), but in other parts of the
    code, the width of the scroll bar _area_ is always calculated as the
    number of scroll bar colums multiplied by the font width (canonical x
    unit).

I think that in some cases the actual display of the scroll bar is
determined by the number of columns.  You can specify a non-integral
width, but it leaves the excess blank.

I don't remember the reason it is done this way, but I do remember 
there was one.