Credit support for 3D Tiles tileset.json

[hpinkos]

Allows credits to be defined as part of tileset.json under extras.cesium.credits

Here's an example of what that might look like:

{
  "asset": {
    "extras": {
      "cesium": {
        "credits": [
          { 
            "html": "this is my credit", 
            "showOnScreen": false 
          }, { 
            "html": "<span>this one uses html</span>", 
            "showOnScreen": true 
          }
        ]
      }
    }
  }
  ...
}

cc @mramato

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[lilleyse]

If it matters, the ion extras are under asset.extras rather than top-level extras. Should this also be under asset.extras for consistency?

[hpinkos]

Updated

[mramato]

@lilleyse while I know extras is a catch all, is there some centralized document we should be maintaining a list of all extras used by the Cesium ecosystem? Seems like formalizing at least our own usage is important.

[emackey]

Should STK and other non-Cesium viewers be displaying these credits to users as well? Do you need cesium in the hierarchy, or is asset.extras.credits good enough? Of course for STK we wouldn't be displaying HTML credits, it would be plain text.

Does Cesium need to sanitize the HTML for untrusted 3D Tiles sources?

FWIW, glTF 2.0 has ended up with a similar construct in its own asset object. Sketchfab's glTF downloads are already including information that looks like this:

  "asset": {
    "extras": {
      "author": "manilov.ap (https://sketchfab.com/manilov.ap)",
      "license": "CC-BY-4.0 (http://creativecommons.org/licenses/by/4.0/)",
      "source": "https://sketchfab.com/models/908985d8ec544638bcd661bc315597ad",
      "title": "Sr71"
    },
    "generator": "Sketchfab-3.20.7",
    "version": "2.0"
  },

[hpinkos]

@emackey Credit already sanitizes the html https://github.com/AnalyticalGraphicsInc/cesium/blob/master/Source/Core/Credit.js#L102

[mramato]

@emackey I think the idea is that we scope these items to cesium or ion initially and if they prove useful eventually we'll promote them to something more standard. I don't think we want to start dumping random properties in at the top level because that makes conflicts too easy.

[emackey]

Yeah I'm just thinking out loud here. If there are credits that are required to be shown, there should be some cross-platform mechanism for communicating that. Some people say glTF didn't do a good enough job of nailing this down before the 2.0 spec shipped. But these are all just suggestions to think about.

[mramato]

I swear I thought I merged this. Thanks @hpinkos!