You can not populate light sources at this time, but you can make luminous objects and populate those. Use very high values for luminosity (10,000, 100,000, or more - the larger the object the higher the value needed). As long as you render with Global Illumination (GI) the luminous objects will light up the surroundings. This is not as easy to deal with as light sources, but can be useful depending on your needs.
The rotation values you specify in a population are ranges. If you specify 0-360, there will be objects anywhere in that range of rotation (i.e. any rotation angle). You cannot specify multiple ranges, but you could use multiple overlapping populations with different ranges to achieve a similar effect.
You can't currently populate volumetrically, but rain would not be best handled this way anyway. You'd need a very high number of drops to create a convincing effect. Instead you can use stretched, low-density clouds for distant rain, or elongated "rain" objects in multiple planar populations close-up. A search for "rain" in the forums will find some topics discussing these techniques.
DoF ("blurred FOV effect") is not currently possible natively within TG2. We are testing development of a function to do this, but it is not yet ready for public use.
Not sure if PNG transparency is supported - you can try it with the appropriate option in the Image Map Shader: under Effects tab, Alpha As Opacity.
P.S. I also moved your topic to the right place.
- Oshyan
