Problems with label backgrounds

[mramato]

#4886 appears to cause problems for labels with backgrounds:

Run http://localhost:8080/Apps/Sandcastle/index.html?src=Ground%20Clamping.html&label=Showcases

The label text should be opaque and the background translucent, but there's an issue that makes the font appear as if it's behind it's background (not always). @bagnell thinks this is a draw order issue.

CC @emackey

[pjcozzi]

Perhaps the background is not getting the new blendOption set correctly?

Otherwise, are we sure the background billboard collection is always added before the label billboard collection?

Otherwise, is >= depth test not set?

[emackey]

Does this only happen when clamped to ground? >= depth is set, and the = part is being relied upon, but I think the clamping might make the Z value a bit noisy.

[emackey]

Possibly related to #4736, clamped billboards can shake.

[bagnell]

The problem seems to be sampling the texture. The default used by the texture atlas is linear. For smaller sized fonts, all of the sampled texels have an alpha < 1. You can test this by changing the label collection to use BlendOption.OPAQUE and no text will be drawn.

[pjcozzi]

If we need a workaround for this, we can also force BlendOption.TRANSLUCENT when a background is used. In practice, it will likely often be OK-ish more so then when there is no background.