[birt-charting-dev] Structuring generated SVG output

[Sheldon Lee-Loy <sleeloy@xxxxxxxxxx>]

I've been looking at the current code
base of the Chart Engine and I have some concerns regarding the drawing
order of the charts.  

As you know there's a notifyStuctureChanged
on the RuntimeContext class that signals the SVG renderer to structure
the generated output.  Adding "structure" in this case means
grouping SVG drawing primitives.  For example, in SVG I can group
a "line" and a "rectangle" as follows:

<g id="mygroup">
<line x1="0" y1="0"
x2="10" y2="10"/>
<rect x="0" y="0"
width="10" height="10"/>
</g>

The above generated output relies on
the fact that the notificaiton happens before and after drawing the line
and rectangle.  However, the charting engine makes use of a cache
that is implemeted by DeferredCache.  From this class I can gather
that it defers the drawing of markers, lines, labels and planes.  Since
the drawing of these chart components are "deferred" the notification
of the structural change will not correctly group these elements.  The
resulting generated output is as follows:

<g id="mygroup">
</g>
<line x1="0" y1="0"
x2="10" y2="10"/>
<rect x="0" y="0"
width="10" height="10"/>

I realize the existence of the DeferredCache
object provides some form of optimization.  However, I'm curious why
this class only has "add" methods. Shouldn't there be getter
methods on this class to reuse cached objects?  I would like to understand
the usefulness of this class and figure out how to corretly notify the
svg renderer when to group drawing primitives.

Thanks,

Sheldon.