purplemonkey
Very cool! for the trees you can try creating compound colliders by using a thin cyclinder collider for the trunk and a sphere for the leafy ball. In debug mode you can trial and error and visualize the position of any extra colliders you add. this all has to be done with action however you can make it automated in the on-created trigger.
Prominent
You shouldn't need to mess around with manual rendering. If you make your scene background have 0 alpha and layer view-ports you can layer renders, however semi transparency wont cross between layers cause of the three.js renderer design. I will add more manual rendering features when I get a chance since you seem to be expressing interest and it wont take much work.
All transparent objects SHOULD render last, as this is the way transparency is generally handled in forward renderers. Opaque objects render in any order and sort using the z-buffer, and at the end transparent objects/sprites are sorted based on camera view-plane distance and rendered back to front. This should minimize all artifacts unless objects intersect, which is a problem that has no easy solution and is present in even modern renderers. If sprites are rendering last after the back to front rendering of transparent objects thats a three.js bug, but i dont recall this being the case.
http://stackoverflow.com/questions/8763 ... r-in-webgl
An image would help me diagnose what the issue you're having is. usually playing with material depth setting values and preventing the sprites/semi transparent objects from writing to the z-buffer works well, especially if its for smoke or special effects like explosions which utilize blending. Transparency is just an overall annoying problem. Sometimes the best solution is to not use a sprite at all, and instead a piece of flat geometry which is a cutout of the silhouette, so that the object can be opaque or mostly opaque, and the artifacts are minimized cause theres no edge-cases that lead to really bad transparency occlusion problems.
Thanks.. I tried using viewports, and I'm able to create a skybox this way.
The other issue I had with sprites was what that link you have describes. A sprite is behind the geometry and so the part covered doesn't get rendered even if material is transparent. I can probably work around it by using models like you suggest, and putting stuff in another viewport with alpha if I have stuff that should render over any sprites..
does it require more processing to render multiple viewports?.. would it be more efficient to render to one? If it's more efficient to render to just one, adding the manual rendering actions would still be useful.