max rtt help

rooster

I want to render an object with an opacity map down onto the lowpoly, but if I include it in the render list the transparent area of the object shows up black instead of letting through the rays.. makes sense I guess but is there any way around it?

CrazyButcher

I just tried and it does show in the image's alpha. the saved file (alpha map) contains the info in both rgb and alpha channel (max9-32 bit)

rooster

thanks man, not sure if I described my problem accurately enough, I want to have a normal hi-to low poly render to texture (diffuse), but with alphad objects included in the render to texture. If you do that, the alpha areas in the diffuse are rendered black instead of whatever should be beneath.. Ive just tried rendering the alpha objects seperate so I can combine them in PS, but most of these objects overlap, and I notice that the alphas dont seem to combine they just get overlaid so the black at the edges of polygons are visible on top of other alpha areas.. if anyone can get overlapping alphas to work I'll buy you a pint sometime

edit: this is odd, when I render an alphad plane against the standard bg, the alpha channel is square instead of the shape of the plane alpha.. am I missing a setting somewhere or what? buh

Sage

Rooster have you tried switching to the raytrace renderer? It's probably just a typical limitation the renderer has. Other 3D apps would do something similar, in my case if I used billboards that had alpha mapped trees with fog and rendered the plane would show up, very annoying. The worst case would be to have to cut that crap out with the cut tool.

Alex

Eric Chadwick

Won't work. RTT renders from the POV of the UV itself, so if you have overlaps in the UV, one chunk will be rendered after the other, completely overwriting the previous pixels.

Instead you might try a script/plugin that unwraps your mesh, converting it from UV space to model space. Then you can render that mesh using the regular renderer instead of RTT.

rooster

cheers eric. any ideas why the alpha isnt showing up in a straight forward render? I thought it did it by default
edit: actually I think you're misunderstanding me, I have some floating alpha planes above the low poly I want to render (think floating high poly geometry, except with alpha). the low poly has no overlapping uvs, the floating poly planes overlap each other though
I'll post some pics

Eric Chadwick

If it doesn't show up correct in the scanline renderer then you're screwed no matter what. How do you have the Opacity channel set? Are you using an alpha channel? Is it a Standard material?

rooster

standard material with alpha as opacity, I could have sworn I've used alpha planes with rendered transparency before though, not sure whats missing.. surely its possible to have alpha channel transparency show up in the default renderer opacity?

CrazyButcher

it probably is a flaw in the scanline renderer, that simply stops the ray on first hit (even if the material says its transparent)

rooster

hmm the transparency comes through in a standard mental ray render, but the mental ray rtt turns out hideous.. blah

rooster

I got it working in mental ray now, after some weird glitchy renders first off. The result doesnt look amazing tbh its just rendered down shrub planes but its a decent base to work off now

MoP

For reference can you tell us what you changed to stop mental ray doing glitchy renders when using RTT?

rooster

er I'd love to not 100% sure.. the difference seemed to be when I put a negative push on my lowpoly bake mesh, which has fixed dodgy mr amb occ bakes for me in the past. I can't say for sure thats what it was but I got a working bake so