Re: doc-view.el --- View PDF/PostScript/DVI files in Emacs

[David Kastrup <dak@gnu.org>]

Tassilo Horn <tassilo@member.fsf.org> writes:

> David Kastrup <dak@gnu.org> writes:
>
> Hi David,
>
>>>>> I changed doc-view.el so that it uses plain ghostscript (plus
>>>>> dvipdfm for DVI files) which gives good results and is about ten
>>>>> times faster than with ImageMagick's convert.
>>>>>
>>>>> The only downside is that I don't know how to cut off the margins.
>>>>> Those waste a lot of buffer space when displaying the image.
>>>>> converts -trim option was very nice for that cause.  Do you know
>>>>> how one can do that with ghostview?
>>>>
>>>> Well, that is one of the things done in preview-latex.  Do you have
>>>> the bounding box information for your images (preview-latex takes
>>>> them from TeX usually)?
>>>
>>> No, how should I get it?  I only have PDF/PS or DVI files with no
>>> sources at all.
>>
>> I am afraid I can't figure out what you are trying to achieve.
>
> Well, when doc-view.el used `convert' I supplied the -trim option to
> it.  This option cuts off the margins by calculating a mimimum
> bounding rectangle around the contents whose outside has background
> color and cuts the outside away.

Sure.  I just think that this is the wrong thing to do for page previews.

>> PDF/PS and DVI files are primarily page-oriented formats.  It does not
>> make sense to display every page with a different size.
>
> I don't agree here.  IMO it wastes too much screen estate to display
> the margins.  When those were cut off I could split my emacs frame
> horizontally and view a PDF doc in one window and have another
> 80-columns window for work.
>
> Now that's not possible anymore because the images contain those
> huge margins.  The only solution is to make the images smaller but
> that makes them hard to read.  And I cannot scroll-left to center
> the image.  Even `C-u 1 C-x <' scrolls too much.

That is an argument for giving better scrolling/margining behavior to
Emacs (you _do_ realize that Emacs can display partial images?).  So
you can add an option for selecting a page area you want to see,
possibly by dragging a rectangle across the image, and then get a
_consistent_ display of margins across your whole document.

>> PDF and PS files can actually change the page format in midstream
>> _if_ that is desired.  Autocropping will complicate the user's
>> handling of page material.  This is different if we are talking
>> about embedded material, graphics and stuff.  In that case, we will
>> be using PDF (which sets its own page size) or EPS.  EPS files
>> carry a bounding box comment: extracting that and using it for
>> setting the rendering bounding box for Ghostscript should do the
>> trick.
>>
>> preview-extract-bb in AUCTeX's preview.el can be used for that
>> purpose.
>
> Yes, but for other files like PDF or DVI that seems not possible.

DVI needs to get converted to PostScript, anyway, doesn't it?

> Currently I don't really see how preview.el could be useful for
> doc-view.  Ok, maybe I could display the first pages before the
> conversion of the rest has finished, but with ghostview conversion
> is so fast that I don't see any benefit that would justify to make
> the code more complex.
>
> For example doc-view on my practicalcommonlisp.pdf which has 528
> pages takes about one minute.  And even this has to be done only one
> time...

preview-latex renders the page you are looking at in a fraction of a
second, even when we are talking about documents with a thousand
pages.  Out of order rendering vastly increases the interactive
response.

> So please give some concrete examples how I could enhance
> doc-view.el with preview.el.

Shrug.  If you don't consider sub-second response times as opposed to
minute delays an enhancement, I am out of my depth guessing what would
qualify as one.

So I am afraid I can't offer anything useful to you.

-- 
David Kastrup