A user asked me whether we would ever have a conditional directive in the OBJ format to let an author vary the look of the object based on weather. My answer:
Definitely not - this is definitely not the intention of conditionals!
The goal of conditionals is to allow authors to cope with multiple "rendering modes" of the engine, where:
- The look of the sim is radically different between the rendering modes and
- The performance cost of working around the lower rendering mode is expensive.
So for example, when shadows are off, you have to use some ATTR state change to drop a fake shadow on an object. This kills instancing, so when shadows are on (and the sim needs more performance), leaving that double shadow is not only ugly, but slow.
The conditional works by fully "stripping" those commands for shadowing from the object, then re-analyzing it.
So the win of conditionals is that you do not pay for what you don't use, because everything is done on load - it's like shipping two highly optimized objects.
But the down-side is: conditionals require scenery to reload, which is slow, disruptive and annyoing. This is why we would never use them for something that is dynamically changing in the sim, like weather or time of day.
We do want to have weather effects, but our approach is going to be very different: to have a "weather map" texture on the object (same UV as the object) indicating what sections of the texture will receive changes to their material due to weather effects. This will allow the object to look progressively more wet over time without a reload as the rain falls.