View Full Version : Help! when is a transparent object not a transparent object....

06-30-2013, 01:54 PM
Hi guys,
Wondering if someone could give me some idea of what's causing an issue for me...

I have a simple cube/plane with an image sequence on it's surface (flames on a black background).

I have several of these cubes/planes in my scene, the idea being that the flames are dotted about the landscape like sprites. Individually they render as expected, however if my camera is looking through one cube to another in the distance, the distant object seems to lose it's transparency and renders the black background around the flames too. It's also a cumulative effect, so with the camera looking through 3 of these cubes the distant cube will have the black background, the middle cube have a grey background, and the font cube renders as normal.

Attached is a zoomed and cropped section of a render. You'll notice the black plane in the distance, look carefully above it and you'll see a grey outline of another plane which id closer and belongs to the flame just poking out from behind the rock on the left.

I have tried changing the way the layers render out by adjusting the blending mode of the flame image sequence (additive, normal, multiply, screen etc). I have tried making the planes both affected and unaffected by the fog in the scene. I have made the planes both double and single sided. I have tried all settings regarding shadow casting and receiving. I have tried adding an inverted image sequence to the transparency control.

Am at a loss as to what could be causing this. Individually the flames look as expected.
Can anyone suggest what might be causing this to happen?

Thanks in advance :)

06-30-2013, 02:06 PM
Try increasing your ray recursion limit in the Render Globals panel.

06-30-2013, 03:20 PM
Try increasing your ray recursion limit in the Render Globals panel.

Smashing! Thank you! Solved the problem and now learning all about ray recursion :-)

06-30-2013, 03:42 PM
Try to keep the number to the minimum or you increase render time. Unless there is some other reason, have Ray Recursion 1 higher than the number of transparent surfaces you are looking through.

07-04-2013, 08:51 AM
I don't know if it will work in this case but you can sometimes get better results by copying the alpha image and using it as a clip map (object properties) . Clip maps tend to render faster than transparency maps and I don't think it'd have the same problem you had here since they effectively cut away the parts of the poly that would otherwise be transparent. The downside to them is that the pixels are either on our off. There is no 20% or 60% transparent with clip maps. That's why they might not work in your scene at least not for the close up flames. Clip maps work best for things with hard edges like leaves or a chain link fence.