Messed up display and incorrect handling of `face' specs on before-strings

Messed up display and incorrect handling of `face' specs on before-strings

[Stefan Monnier]

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Try the nhexl-mode below on a buffer.
You should see that the first line of the buffer is displayed
differently from the rest (the first line is displayed the way I'd want
it).  On the subsequent lines, the `face' properties as well as the
`display' properties on the before-strings seem to be ignored (or
something like that).

This minor mode seems to hit several other bugs, but let's start
with this one since I haven't found easily reproducible test cases for
the other ones yet.


        Stefan



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Re: Messed up display and incorrect handling of `face' specs on before-strings

[Eli Zaretskii]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Date: Tue, 06 Apr 2010 23:13:22 -0400
> 
> Try the nhexl-mode below on a buffer.
> You should see that the first line of the buffer is displayed
> differently from the rest (the first line is displayed the way I'd want
> it).  On the subsequent lines, the `face' properties as well as the
> `display' properties on the before-strings seem to be ignored (or
> something like that).

In which version(s) of Emacs? TTY? GUI? both?

In Emacs 23.1.92 on a TTY I see the ASCII characters on the right
underlined, while the hex part is not.  The other lines are underlined
in the hex part as well.  Also, the first line is 2 columns to the
right after the address part, relative to the other lines.  And the
highlight of the current byte in the hex part does not work on any
line but the first one.

Is this what you meant?

If so, could you perhaps summarize the problems you see in terms of
the underlying features (`display' properties, overlays,
`before-strings', etc.)?  Armed with that knowledge, it would be much
easier to look in the display code what it would do under the
circumstances.

Re: Messed up display and incorrect handling of `face' specs on before-strings

[Stefan Monnier]

>> Try the nhexl-mode below on a buffer.
>> You should see that the first line of the buffer is displayed
>> differently from the rest (the first line is displayed the way I'd want
>> it).  On the subsequent lines, the `face' properties as well as the
>> `display' properties on the before-strings seem to be ignored (or
>> something like that).

> In which version(s) of Emacs? TTY? GUI? both?

I only tested it in GUI, but your tty description indicates it also
shows up for ttys (unsurprisingly).

> In Emacs 23.1.92 on a TTY I see the ASCII characters on the right
> underlined, while the hex part is not.  The other lines are underlined
> in the hex part as well.

That's the kind of discrepency I'm talking about, yes.

> Also, the first line is 2 columns to the right after the address part,
> relative to the other lines.

That as well.

> And the highlight of the current byte in the hex part does not work on
> any line but the first one.

Also.

> Is this what you meant?

Yup.

> If so, could you perhaps summarize the problems you see in terms of
> the underlying features (`display' properties, overlays,
> `before-strings', etc.)?

The first and 3rd issues seem to be due to the fact that `face'
properties on the before-strings of the overlays aren't obeyed except on
the first line.  And the second is the same problem but for the
`display' property.


        Stefan

Re: Messed up display and incorrect handling of `face' specs on before-strings

[Eli Zaretskii]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: emacs-devel@gnu.org
> Date: Wed, 07 Apr 2010 09:46:16 -0400
> 
> The first and 3rd issues seem to be due to the fact that `face'
> properties on the before-strings of the overlays aren't obeyed except on
> the first line.  And the second is the same problem but for the
> `display' property.

Can you construct a simple test case that shows these problems?  I
tried a few, but they all seem to work, so I probably do something
differently than nhexl-mode.el does.  Specifically, I don't know how
to simulate ``non-first lines''.

Re: Messed up display and incorrect handling of `face' specs on before-strings

[Stefan Monnier]

>> The first and 3rd issues seem to be due to the fact that `face'
>> properties on the before-strings of the overlays aren't obeyed except on
>> the first line.  And the second is the same problem but for the
>> `display' property.
> Can you construct a simple test case that shows these problems?

If you look at the code, it's pretty simple.

> I tried a few, but they all seem to work, so I probably do something
> differently than nhexl-mode.el does.  Specifically, I don't know how
> to simulate ``non-first lines''.

If you set nhexl-point to some integer value and then run (nhexl-jit
(point-min) (+ 30 (point-min))) without enabling the mode, you should
get just two overlays and the problem is already visible there.

I think the trick is to have two consecutive overlays, the first with an
after-string and the second with a before-string.


        Stefan