Re: Layered display API (was: bug#18195: 24.3.92; window-screen-lines is not accurate)

[Eli Zaretskii <eliz@gnu.org>]

> Date: Wed, 06 Aug 2014 16:40:37 +0400
> From: Dmitry Gutov <dgutov@yandex.ru>
> CC: rudalics@gmx.at, emacs-devel <emacs-devel@gnu.org>
> 
> Basically, we'd like to be able to display a rectangle with propertized 
> text inside, at an arbitrary position (I would say pixel coordinates, 
> but that might not work well in terminal), so that it would be displayed 
> above the buffer contents.

That you already have, don't you?  The problem is not display, AFAIU,
the problem is the decision where exactly to display it, and the
answer depends on the dimensions of the text and the window.

If some features are missing to achieve the above (and they are not
the 2 mentioned below), then please spell them out, because I thought
the display part was already solved, once the layout is decided.

(And pixel units work quite well on text terminals, except that each
character position is 1 pixel.)

> 1. If the buffer ends (shortly) after the current line, we're forced to 
> pad it with a newline, and then carefully undo that and restore the 
> buffer modification status.

Why can't you include the newline in the overlay string instead?

> 2. If the buffer is already heavily using the `display' text property, 
> or other similar ones, our tooltip positioning also breaks or works 
> unexpectedly. Example: the `report-emacs-bug' buffer 
> (https://github.com/company-mode/company-mode/issues/136).

This is indeed a missing feature.  It should be easy enough to provide
some special kind of display property that would overlay any other
displayed content, but won't that introduce the kind of arms race we
already have with overlay priorities?  IOW, what if more than one
feature wants to have its string displayed on top of everything?

Btw, why doesn't company use normal tooltips on GUI frames and
text-mode menus on a TTY?  Wouldn't that be better?

> Somewhat relatedely, I'd love to be able to sanely display smooth 
> graphics spanning multiple lines in the fringe (or in the area that 
> would replace it)

How is this different from displaying bitmaps that fill the whole
height of a screen line, so that adjacent bitmaps don't leave any
pixels between them?

> Maybe even support buttons?

Clicking on the fringes already works.