Proposal: Support translucent color

[jasollien]

Currently there is no way to make an element translucent, while still keeping the original color.

I suggest that we all agree on a color value that should be treated translucent, example "000000", or similar.

Also, it should be possible to transluce (or color) all elements except some.

[GeorgDangl]

Just a thought, I think right now we can either have three blocks for red, blue, green or four blocks to include transparency. What if just a single block would indicate just a transparency value?

But we should maybe look around a bit more, how such data is expressed in other systems - maybe there's a clever solution that we just don't know😀

[GeorgDangl]

From the docs:

So, we can provide transparency IF we also provide colors, but we can't just add a transparency without also specifying the color.

[ykulbak]

I propose that transparency should be defined directly under the compomenets because it willl be used in a similar fashion to visibility. Clash detection tools, for example, will colour the clashing objects and would apply transparency or a wireframe view to the surrounding objects to retain context (see image).
I propose we create a transparency object which would follow the same pattern as visibility. It would have a default_transparency directive and a set of exceptions to support making "everything transparent" and then highlight a small number of objects.
Transparency will be subject to visibility - a hidden/invisible object will not become visible by having a transparency assignment.

[pasi-paasiala]

@ykulbak I like this idea. This way we wouldn't need to specify the transparency for each component. It'd be just a rendering hint how to show rest of the model.

[GeorgDangl]

We've discussed it in the call, we'll go with that approach😀

[ykulbak]

Discussion summary:
We discussed the BCF-XML pull request on the fortnightly call.

• General agreement with the approach
• The proposal allows categorising components as translucent or opaque but it doesn't allow specifying how translucent the components should be. Should we allow specifying the translucency of components?
  -- Agreed that if translucency level should be specified then it would be specified as a [0-1] xs:decimal where 0 indicates complete transparency and 1 indicates full opacity
  -- Proposed approach - leave the rendering of translucent components to the vendors who will ensure that the translucency level provides the best experience for their users.
  -- Alternative approach - specify translucency for each component.
  -- Alternative approach - specify translucency for each component type.
  -- Alternative approach - specify a single "global" translucency number for the viewpoint.
• Concern: the XSD definition for translucency is a duplication of the visibility XSD with minor adjustments. Should we generalise and reuse a single XML schema definition for both?

It was decided to pause and defer the discussion to a future meeting with a greater number of participants.

[GeorgDangl]

We just discussed it in a larger group in the call. The linked PR in the BCF XML repo looks good, and we'll do it that way😀

[GeorgDangl]

Closed with #326