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Re: [xsl] Re: Re: how to optimize recursive algorithm?

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Comments interspersed with text.


----- Original Message -----
From: "Dimitre Novatchev" <dnovatchev@xxxxxxxxx>
To: <xsl-list@xxxxxxxxxxxxxxxxxxxxxx>
Sent: Saturday, November 29, 2003 09:24
Subject: [xsl] Re: Re: how to optimize recursive algorithm?


> > I want to represent this document graphically (in SVG) as a tree
structure
> > like this:
> >
> > root
> >  |-------------<------------------|
> >  |--- ab-------->-----------------|
> >  |--- longname -->----- xyz-->---|
> >  |                             |--- tuop-->--|
> >  |--- last -------->----------------|
> >
> >
> > The problem I submitted refers to the calculation of the width of the
> branch
> > on the right hand side of each element's name (plus the first branch
> > represented as a path going backwards) that should be aligned to the
> > rightmost position for all elements.
> > Its total length is the maximum of the sum of the length of all elements
>
> Here you are talking about "the maximum of the sum of the length of all
> elements" ... ?
>
> What is a "length of an element" ?
>

Since I was describing a graphical output I overlooked the specification of
pixels as length unit. I am sorry for that.
The length of an element is the element's name rendered in a certain font,
which is corresponding to the width of the "bounding box" surrounding the
text.
I need to know in advance the horizontal dimension of this bounding box,
because I want to add certain graphical elements basing on its width.
The length, or the width if you prefer, of the text element therefore is its
length in pixels. To cut a long story short, say the length of an element to
be proportional to its character length, according roughly to a formula like
this:

length(name) *  fontsize * 3 / 4

In reality the formula is more complex because of kerning and spacing
values, but let's ignore them in this exercise, because it is also
reasonable to use fixed width fonts which avoid such annoying complication.


> "the maximum of the sum of the length of all elements" should be just "the
> sum of the length of all elements" -- a sum is just a single number, it is
> not meningful to try to find the maximum of a single number.
>

I must retrieve the maximum value because I need to align the vertical lines
to the rightmost position, as I tried to represent in the picture.
The vertical pipes theoretically should be aligned with each other. Their
position corresponds to the position of the widest branch plus a certain
delta value.
In order to retrieve this value, I need to know where is located the element
having the maximum x coordinate.
The x coordinate depends not only on the length of the element itself, but
also on the length of its ancestors, and this is why it is a sum (when there
are more elements sitting on a branch) and not a single number (unless there
is just one element).
It is perfectly possible to have a situation where a single element with a
very long name takes more space than two short elements, so I cannot make
any assumption basing on the depth of an element to decide which one is the
most displaced to the right.
The maximum value is the result of adding up the length of one or more
elements belonging to the same axis (I called it branch), inside a certain
boundary, in the example I gave, the boundary is represented by the node
called <all>. The elements inside an <all> group must be drawn on top of
each other and since they can be repeated, I want to draw a straight
connector on the right hand side of the element joining a vertical line that
will convey the concept of repeatability of the elements (as in the poor
picture I provided).

The position of this vertical line, but also the rightmost x position of the
connector line drawn starting from the rightmost element sitting on a
branch, depends on the maximum x value within the <all> group.
So, unless I am able to calculate the value beforehand, it will be
(re)calculated for each element(s) belonging to the <all> group, wasting a
lot of time.

So, describing the situation occurring in the given example, I must find the
largest value (the maximum) among:

width-in-pixels("ab") + deltaX
width-in-pixels("longname") + deltaX + width-in-pixels("xyz") + deltaX
width-in-pixels("longname") + deltaX + width-in-pixels("tuop") + deltaX
width-in-pixels("last") + deltaX

where deltaX is a fixed value of padding space.


> > residing on each "branch" plus a certain fixed amount to leave some room
> > between the elements.
> >
> > In this case it would be the maximum between:
>
> Now you are just looking for the maximum of several numbers, not the
maximum
> of their sum.
>
> > the length of "ab"
> > the length of "longname" plus "xyz"
> > the length of  "longname" plus "tuop".
> > the length of "last".
> >
>
> Summary:
>    It is not clear what you want to achieve. However, I guess the
following
> link will be useful:
>
> http://skew.org/xml/stylesheets/treeview/ascii/


What I want to achieve is similar, although in graphical format, using SVG,
and much more complex, the practical purpose is rather different also.
You can see a sample of output of this transformation at the following
address:

http://www.yocoya.com/samples/embed_alter_database.html

An SVG plugin is required to display the internal frame.

This page gives you an idea of the graphical output obtained by applying the
transformation, although it doesn't constitute an example of the problem
discussed here because there are no repeating groups of elements.

>
> Also, in case you need to find the element with the maximum depth, this
> question has been asked before and has a nice and efficient solution (e.g.
> using FXSL) -- see
> http://sources.redhat.com/ml/xsl-list/2002-05/msg00611.html
>

It looks similar to the the "function" I am already using, good!


> Pardon me in case my guesses are wrong.
>
>
>
> =====
> Cheers,
>
> Dimitre Novatchev.
> http://fxsl.sourceforge.net/ -- the home of FXSL
>


Thanks for your help anyway,

Flavio



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