#3 Support alpha channels for geometry and text

[Drew Noakes]

Currently only polygons can specify an opacity.

We're using RoboViz's debug capabilities a *lot* and the screen can get pretty cluttered. Furthermore, having alpha blending on lines and circles can be used to show an additional dimension of the data, such as confidence, importance, distance, etc.

Mostly I would like this on lines and circles. If it's possible for text too, awesome.

I know that this would probably require new message types, as the current binary format does now allow for adding the A after the RGB. I guess you could stick it on the end too. That's a bit yuck.

[Justin Stoecker]

I will just change the message formats; it may break some drawings but is an easy change in client code.

I avoided adding transparency to all drawings for a simple reason: it requires attention to the draw order of objects. Achieving order-independent transparency is not cheap or easy to implement efficiently.