bug#10960: linum-mode does not work properly when changing font size

[Stefan Monnier <monnier@iro.umontreal.ca>]

>> You mean, that text-scale-* makes the problem more common significant?
>> Maybe so, yes.  But I don't think that just special-handling
>> text-scale-* would be a good solution.
> Special-casing it was not what I had in mind.

Actually, what you propose does just that.

>> We need some more general way to adjust the size of the margin to
>> the size of the images&text displayed there, so as to handle
>> non-default faces, proportional text, ...

> It all boils down to calculating the size of the margins in pixels.
> The key to that is window_box_width, which uses
> WINDOW_FRAME_COLUMN_WIDTH to convert columns into pixels, and
> WINDOW_FRAME_COLUMN_WIDTH returns the "canonical" width of a column,
> which is an average width of the default face's font.
> So all it takes is to make that calculation aware of face remapping,
> images displayed in the margin, etc.

OK, so rather than special casing text-scale-* you suggest to special
case frame-remapping: same problem.  It still won't account for
non-default faces, proportional fonts, and other display features,


        Stefan