Re: Several suggestions for image support

[David Kastrup <dak@gnu.org>]

storm@cua.dk (Kim F. Storm) writes:

> Stefan Monnier <monnier@iro.umontreal.ca> writes:
> 
> > I already suggested to use two new primitives (that have incidentally
> > been requested for other purpose):
> >
> >      point-to-pixel
> > and
> >      pixel-to-point
> >
> > which turn a (displayed) buffer position into a display position
> > and vice versa.  All the rest should then be reasonably easy to do
> > in Elisp.
> 
> Actually, these are easy to implement, so I'll do that.
> 
> They will return a lispy position like the one returned by
> event-start for a mouse click at the given point/position.
> 
> In this context, the names posn-at-point and posn-at-x-y are better,
> as they directly relate to the corresponding posn- macros.
> 
> As a side bonus, pos-visible-in-window-p will be changed to return a
> list [when partially arg is non-nil]:
> 
>         (x y top bottom)
> 
> which specifies the x and y position of POS, and the number of pixels
> not visible at the top and bottom of the corresponding window line.

Is this really necessary?  I think that it should be sufficient if we
just returned x and y; if one wants to see which of the pixels are
actually off-screen, then checking x and y for negative coordinates
or coordinates that (if we add the object's x and y extent) pass
beyond the screen dimension.  I think that the situation where one
would check for partial visibility is rare enough that complicating
the data format is not warranted.

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum