Re: DOCBOOK-APPS: How to select <imageobject> alternative in<mediaobject>?

[Bob Stayton <bobs@caldera.com>]

On Sun, Nov 24, 2002 at 10:16:13PM +0100, Bart Schuller wrote:
> On Sun, Nov 24, 2002 at 09:50:40PM +0100, Steinar Bang wrote:
> > What's the proper way to select a different <imageobject> for HTML and
> > XSL:FO, in a <mediaobject> containing two PNGs?  (actually the same
> > PNG but with different scaling)

The current XSL stylesheet process uses the first
acceptable *object element within a mediaobject.
By default, "acceptable" means the filename extension
appears in a list of filename extensions for that processor.

> I'm currently doing it by using GIF for HTML and PNG for FO, which
> happens to "just work".

Well, this lucky trick won't work if you switch to XEP
for your FO processing because XEP accepts GIF as well.
Check out the 'graphic.extensions' parameter defined in
fo/graphics.xsl to see which extensions are acceptable 
for each fo processor.
 
> But the doubled images both on disk and in authoring environments bother
> me too, so I'm contemplating only keeping the <imagedata> elements with
> scaling and write a simple XSLT file to make a copy but without the
> scaling info. The copy would then be transformed to HTML, the original
> to FO.
> 
> Now that I'm writing it down like this, it could also be solved by
> introducing a new parameter to the HTML transform, something like
> "disable-image-scaling".
> 
> I've just added it as Feature Request 643237 on sourceforge.

Another way would be to keep the two <imageobject>
elements, add role values to them, and customize the
'is.acceptable.mediaobject' template found in
common/common.xsl.  That template is used when there is
more than one imageobject in a mediaobject.  The template
returns '1' if an imageobject is
acceptable, or '0' if not.  If '0', then the processor
tries the next imageobject within the mediaobject.

You could customize 'is.acceptable.mediaobject' for HTML by
copying the whole template to your HTML customization layer
and changing the final xsl:choose statement to start with:

<xsl:choose>
  <xsl:when test="$object/@role = 'fo'">0</xsl:when>
  ...

By returning zero, the HTML stylesheet rejects any imageobjects
whose role="fo".  Do the reverse for your FO customization
layer, rejecting role="html" imageobjects.

-- 

Bob Stayton                                 400 Encinal Street
Publications Architect                      Santa Cruz, CA  95060
Technical Publications                      voice: (831) 427-7796
The SCO Group                               fax:   (831) 429-1887
                                            email: bobs@sco.com