Re: [xsl] absolute position fo:block to attain magazine like layout

Subject: Re: [xsl] absolute position fo:block to attain magazine like layout
From: "W. Eliot Kimber" <eliot@xxxxxxxxxx>
Date: Tue, 12 Nov 2002 21:37:05 -0600
G. Ken Holman wrote:
At 2002-11-12 10:50 -0600, W. Eliot Kimber wrote:

It just occurred to me that you could possibly fake this if you know the exact geometry of everything:
XSL-FO 1.0 doesn't have any synchronization constructs or ways to determine how far down a column one has been, in order to position the side float.

At least I'm pretty sure it cannot be done, but, Eliot, you've managed magic in the past.

Included below is one solution that works with XSL Formatter (but not with XEP--it isn't doing the first-column end-ward side float and I don't know why not--the XEP docs indicate that side floats are supported; also, XEP positions absolutely positioned blocks relative to the page, not the containing refenence area--this is a documented restriction, so I would have to calculate its offset differently for XEP). I think this example is 100% correct WRT to the FO spec, but it's always possible I'm inadvertantly taking advantage of a bug or relaxed constraint of a particular implementation.

The restriction on this approach is that you have to be able to explicitly start both columns--this obviously won't satisfy the requirement to do this in the middle of an arbitrarily flowed column sequence. But I think that it could satisfy the start-page sequence use case. Also, I don't think you'd be able to achieve the same effect at the bottom of a column (not without column-based after floats).

I've also been thinking about the posibility of applying a two-layer approach to this type of layout problem, where you use a second XML document to bind presentation-specific information to more generic content and then combine them at XSLT time. For example, you could have a separate layer that links to the paragraphs that need to start new columns in order to be able to "synchronize" the two columns in order to anchor the floats needed to achieve the effect in my example above. This second layer could also include the data needed to populate the decorative elements, such as the overlayed block in my sample. But I haven't really thought this out so I don't know if it's actually practical or useful. I know another intriguing idea was posted here or in one of the other FO-related forums not too long ago, although I haven't had a chance to follow up on that idea yet.

Of course, it might be just as easy to add format tweaking attributes to the elements in question. There's something to be said for by-hand two-pass format tuning--it's cheap, it's easy, and it does work (and it's been SOP for word processing software for more than a decade).



FO sample:

<?xml version="1.0"?>
<fo:root xmlns:fo=""; font-family="Helvetica" font-size="12pt" line-height="120%" xml:lang="en">
<fo:simple-page-master master-name="base-page" page-height="11in" page-width="8.5in">
<fo:region-body margin-top="2in" margin-left="0.5in" margin-right="0.5in"/>
<fo:simple-page-master master-name="first-page" page-height="11in" page-width="8.5in">
<fo:region-before extent="2in"/>
<fo:region-body margin-top="3in" margin-left="0.5in" margin-right="0.5in" column-count="2" column-gap="0.25in"/>
<fo:page-sequence master-reference="first-page">
<fo:flow flow-name="xsl-region-body">
<fo:block border-width="1pt"
<fo:float float="end">
block-progression-dimension="3in - 1.5in"
inline-progression-dimension="(7.5in div 4) - (0.25in div 2)"
leader-length="100%">Column 1 </fo:leader>
<fo:block>Test of the ability to create an absolutely positioned block
in the middle of two columns that appears to intrude into
both columns.</fo:block>
<fo:block space-before="12pt">The areas generated by the fo:block-container
formatting object have a value of "true" for the is-referencearea.</fo:block>
<fo:block space-before="12pt">The size of the viewport-area and the
reference-area has to be fixed in the inline-progression-direction. It
must be specified unless the inline-progression-direction is parallel to
the inline-progression-direction of
the reference-area into which the areas generated by this flow object are placed.
<fo:float float="start">
block-progression-dimension="3in - 1.5in"
inline-progression-dimension="(7.5in div 4) - (0.25in div 2)"
<fo:leader font-weight="bold" leader-pattern="use-content" leader-length="100%">Column 2 </fo:leader>
<fo:block space-before="12pt">The fo:block-container flow object is used to generate a block-level reference-area, typically containing
text blocks with a different writing-mode. In addition, it can also be used with a different referenceorientation
to rotate its content.</fo:block>
<fo:block space-before="12pt">The fo:block-container formatting object generates one or more viewport/reference pairs. The fo:blockcontainer
returns these areas and any page-level-out-of-line areas returned by the children of the fo:blockcontainer.</fo:block>
inline-progression-dimension="7.5in div 2"
left="(-7.5in div 4) - (0.25in div 2)"
>Center treatment</fo:block>
W. Eliot Kimber, eliot@xxxxxxxxxx
Consultant, ISOGEN International

1016 La Posada Dr., Suite 240
Austin, TX  78752 Phone: 512.656.4139

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