Re: DOCBOOK-APPS: Problem with centering images using DSSSLstylesheets?

[Nik Clayton <nik at nothing-going-on dot demon dot co dot uk>]

[cc'd to Norm]

On Wed, Feb 21, 2001 at 05:46:52PM -0500, Dan York wrote:
> I'm having a problem with not being able to center graphics in either
> the HTML or PDF files that I am generating.

Bug in the stylesheets.

I've got a patch, but it might need some work.  It also only applies to
the HTML stylesheets.

If you look at the generated HTML, you'll see something like

     <div class="MEDIAOBJECT">
       <p><img src="foo.png" alt="Foo"></p>
     </div>

Tracing through Norm's code, it's something like this (in
.../html/db31.dsl).

 1.  The code in "(element mediaobject ... )" runs.  This code creates
     the DIV element and the P element inside it.

     This code does not know which (if any) elements are going to occur
     inside the MediaObject element.

     Control is handed to the $mediaobject$ function.

 2.  $mediaobject$ calls various other functions to work out which 
     elements inside the MediaObject element are displayable.  Inside
     this function "dobject" means the displayable object (chosen by 
     select-displayable-object).  In your example, dobject will end up
     being a reference to the ImageObject element.

 3.  "(element imageobject ... )" doesn't do anything except hand off
     processing to its children.  In your case, the ImageData element.

 4.  "(element imagedata ... )" can look at the ImageData attributes,
     and do appropriate things with the Align attribute.  But at this
     point we're too late.

The patch removes the generation of the P element from the MediaObject
element, and adds it to each of the ImageData, AudioData, and VideoData
elements instead.

This sort of works.  Images are aligned as you want.  However, it's then
not possible to do 'floating' images (the equivalent of <img
align="right"> in HTML), and the caption (if you have one) still appears
on the left margin.

A better approach might be to move the processing in to the
$mediaobject$ function.  Let it work out which is the displayable object
(which it already does) then have it walk down the tree until it reaches
the *data element, and pull out the align value.  Then it can create
paragraphs for the *data content and the caption using this data.

That's left as an exercise for the reader.  As is creating an
default-image-alignment variable that could be used to specify how
images line up normally.

N
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--- db31.dsl.org	Thu Feb 22 16:46:28 2001
+++ db31.dsl	Thu Feb 22 17:49:40 2001
@@ -86,8 +86,7 @@
 (element mediaobject
   (make element gi: "DIV"
 	attributes: (list (list "CLASS" (gi)))
-	(make element gi: "P"
-	      ($mediaobject$))))
+    ($mediaobject$)))
 
 (element inlinemediaobject
   (make element gi: "SPAN"
@@ -108,16 +107,18 @@
 
 (element videodata
   (let ((filename (data-filename (current-node))))
-    (make element gi: "EMBED"
-	  attributes: (list (list "SRC" filename)))))
+    (make element gi: "P"
+      (make element gi: "EMBED"
+  	    attributes: (list (list "SRC" filename))))))
 
 (element audioobject
   (process-children))
 
 (element audiodata
   (let ((filename (data-filename (current-node))))
-    (make element gi: "EMBED"
-	  attributes: (list (list "SRC" filename)))))
+    (make element gi: "P"
+      (make element gi: "EMBED"
+	    attributes: (list (list "SRC" filename))))))
 
 (element imageobject
   (process-children))
@@ -140,6 +141,7 @@
 				     (data (node-list-first phrase))))))))
 	 (fileref   (attribute-string (normalize "fileref")))
 	 (entityref (attribute-string (normalize "entityref")))
+	 (align     (attribute-string (normalize "align")))
 	 (format    (if (attribute-string (normalize "format"))
 			(attribute-string (normalize "format"))
 			(if entityref
@@ -149,12 +151,14 @@
 	(if fileref
 	    (include-file fileref)
 	    (include-file (entity-generated-system-id entityref)))
-	(make element gi: "IMG"
-	      attributes: (append
-			   (list (list "SRC" filename))
-			   (if alttext
-			       (list (list "ALT" alttext))
-			       '()))))))
+        (make element gi: "P"
+              attributes: (if align (list (list "ALIGN" align)) '())
+	  (make element gi: "IMG"
+	        attributes: (append
+	 		     (list (list "SRC" filename))
+			     (if alttext
+			         (list (list "ALT" alttext))
+			         '())))))))
 
 (element textobject
   (make element gi: "DIV"