Volume lighting and transparency

[robchis]

Scene: Night, inside a dusty old room with panes of dusty/dirty & broken glass in the window. Moonlight streaming in (ignore the moon image in the background).

I need to create the effect of rays of light from the cracks in the window lighting up the dust inside the room, AND show the two-tone lighting coming from the remaining glass and the holes in the glass .

The glass is several planes that have been sliced with the "cut faces tool", with a simple phong shader at about 50% transparency.

The rays of light are from a distant spotlight, with volume light (light fog) turned on, and using depth map shadows.

The two-tone shadows on the floor are achieved by a duplicate spotlight (in the same position), but using raytrace shadows.

The moon and the trees are actually a plane just outside the room (with casting and recieving shadows turned off), so as to block visibility of any depth of the volume light.

The problem is, the volume lighting, when it hits the glass, causes it to be intensely lit - turning white... This is what I'm trying to get rid of... I need the glass to be visible (partly transparent) and not blown out by the volume light.

I've heard there's a workaround for this situation, but I haven't found it yet.

Possible somehow clipping the visible range of the cone of volume light so it starts after the panes of glass? I've tried leaving the primary visibility of the panes of glass off, and having duplicates of all the panes and glass in the same place but with everything in their rendering stats turned off except for primary visibility, but the problem returns...

Could somebody help me?

An image of what I'm talking about is here:
http://users.tpg.com.au/robchis/glassQuad.jpg

Thanks everybody

[joojaa]

ok this is tricky but can be done... volume lights in maya work on depthmaps so trancparency is not realy possible but...

ok two ways of faking this!

Way one is to make use of 1 light and a depthmap shadow that prefeerebly has not got mid distance maps on test this depends if your geo actaualy has volume or not!

Make the light, look trough it in one viewport adjust the temporary camera to match the light render without fog with a white background (or the color of your light should it not be white), with only the primary shadowcasting gometry visible. Then assign this map to the shadow color! It would be preffereable to make all materials totaly matte and untransparents black.

Method 2 make every portion of the scene have a independent light for shadowcasting purposes. Make the primary light as is but the others infinitely small in appearnce then make the shadow color a huge negative multiple untill you find the saturation you want. Once you get into this its not hard to set up. Then light link the stuff accurately to spesific parts.

you can offcourse do it in mental-ray whith ray marching with a huge speed hit.

[robchis]

Thanks Joojaa... but I should mention that unfortunately, the camera will be moving around, and method one seems suited to a stationary shot.

Method 2 sounds a lot more promising, albiet moving into a realm beyond anything I've done before... I'll try giving it a shot!

Any other alternate solutions, anybody (in case Joojaa's methods aren't the ones I'm looking for)?

[joojaa]

method 1 works for any shot. depending... if the light moves then you need to do a extra pass for it. than map the sequence.

method 2 offcourse does this if you need to easily. Still method 1 is faster.

And cameara moving offcourse doesent affect lights! if light is stationary then it needs to be calculated once.

i have ademo of those somewhere let me dig it up!

unless you want to use mental ray then im afaraid your running out of options!