ISSUE: do "graphically invisible" objects receive events?

[Lofton Henderson <lofton@rockynet.com>]

 From Dieter's comments:
http://lists.oasis-open.org/archives/cgmo-webcgm/200506/msg00021.html

ISSUE:  do "graphically invisible" objects
receive events?

3.2.1.1. grobject

1.      Definition of mouse region

Question: Do we need to add verbiage for degenerate cases, e.g. a solid fill using a transparent RGBA or a transparency escape?

DISCUSSION.  Objects that are invisible by virtue of the
'visibility' ApsAttr cannot receive events.  What about objects that
are invisible by virtue of graphical attributes, like
transparency?

For reference, I looked at SVG 1.1 [1].  It has a rich
pointer-events property:

    visiblePainted | visibleFill | visibleStroke | visible |
    painted | fill | stroke | all | none | inherit
    Initial:    visiblePainted
[...]
visiblePainted
    The given element can be the target element for pointer events when the 'visibility' property is set to visible and when the pointer is over a "painted" area. The pointer is over a painted area if it is over the interior (i.e., fill) of the element and the 'fill' property is set to a value other than 'none' or it is over the perimeter (i.e., stroke) of the element and the 'stroke' property is set to a value other than 'none'.

Since we do not have such a control, it would be nice if our answer to
this question matched the SVG default, visiblePainted.  But SVG
doesn't address the question of transparency for fill and stroke. 
However, in the same section note that it does say this about raster
elements:

> For raster images, hit detection is
> either performed on a whole-image basis (i.e., the rectangular area for
> the image is one of the determinants for whether the image receives the
> event) or on a per-pixel basic (i.e., the alpha values for pixels under
> the pointer help determine whether the image receives the
> event):
>
>     * The value visiblePainted means that the raster image
> can receive events anywhere within the bounds of the image if any pixel
> from the raster image which is under the pointer is not fully
> transparent [ed's emphasis], with the additional requirement that the
> 'visibility' property is set to visible.

I am tempted to guess that SVG intended the "not fully
transparent" for the fill and stroke also -- consistently with
raster -- and failure to address it is an oversight. Therefore...

RECOMMENDATION:  add "not fully transparent" to the
conditions that make define a mouse region as eligible for receiving
mouse events (pick, etc).

-Lofton.

[1]
http://www.w3.org/TR/SVG11/interact.html#PointerEventsProperty