Check-in [c368e0d5ea]

# TIP 553: Ellipses: the Alternative to Scrolling and Wrapping
        Author:         Donal K. Fellows <[email protected]>
        State:          Draft
        Type:           Project
        Vote:           Pending
        Created:        07-Nov-2019
        Post-History:
        Tcl-Version:    8.7
        Keywords:       Tk, label, listbox, entry
-----

# Abstract

This TIP proposes a mechanism for getting Tk widgets to insert an ellipsis
instead of wrapping or scrolling (in widgets where this makes sense) a line
of text.

# Rationale

Adding an ellipsis when a piece of text is too wide to be shown in its
entirety is a common modern GUI idiom, and one that is relatively easily
implemented in Tcl/Tk as is. However, we do this in general by measuring the
text (with `font measure`) by hand and determining where the ellipsis should
be inserted, and then modifying the text itself to insert the ellipsis. This
makes it difficult to make the position of the ellipsis change as the width
of the widget changes, as we have to add code that observes the change to the
View (via a `<Configure>` event on the widget) and update the Model in
response, despite the _true underlying_ Model not changing at all.

Instead, we should have the widgets do the work for us, so that we can just
indicate what the true text is and tell Tk that it should insert ellipses as
and where required without further user intervention.

# Specification

When a widget supports applying an ellipsis, it will take a new option,
`-ellipsis`, that will allow the specification of an ellipsis (as a string;
there are multiple ways of expressing an ellipsis, and the right choice
depends on other features of the interface) that gives a symbol to use after
trimming off the text _at a character boundary_ in order for the text
including the ellipsis to fit inside the widget's width. 

For label-based widgets (i.e., labels, buttons, checkbuttons, radiobuttons)
the existing `-wraplength` will be used as the limit width for ellipsis
insertion, where defined. Otherwise the width of the text part of the
widget (based on the widget width and the impact of any compound images) will
be used.

For the entry-based and listbox-based widgets (including spinboxes and
comboboxes) the widget width will be used.

Note that the ellipsis insertion code will always use the font set in the
widget, and widgets that are so narrow that they cannot display the ellipsis
itself may look strange.

# Implementation

To be done.

# Copyright

This document is placed in public domain.