Rect light texture alpha issue

[seandunderdale]

Im having an issue in 3.6. Ive got a rect light with an image of a treeline loaded into the texture slot. I have a luminance map loaded into the tex alpha slot to cut the sky out and keep the darker treeline silhouette. When I render with this next to a car, so I can also see the light, it looks like the alpha is working and cuts out the sky, but in the reflections on the car, there is no cutout and it looks like the alpha map isnt working. The part that should be cut out is just grey. Ive ticked alpha is luminance and tried different file formats.

[SonyBoy]

That's a pretty unorthodox use of a light and light texture. Is there some reason you need to do this with a rect light? If you're basically just creating textured cards you're probably better off using simple planes. In any case, the attr. that controls a rect light's alpha is the "Rect Text A" underneath the texture slot. Have you tried setting this to 0?

[seandunderdale]

Yeh Ive tried setting it to 0. That results in the same reflection in the car, but the light disappears from primary visibility (Not a bad thing since I don't actually want to see the light) . The reason Im doing this with a light is because this is how I light with gradients when I do studio stuff, so it's pretty common in that regard. Adding a ramp to a light in a studio to create falloffs that blend and dont have harsh edges to lights. Lights refresh way faster than geo in RT so doing it with lights makes sense to me. My job generally requires me to recreate the same lighting and reflections that the stand in car had on location. This means often creating my own treeline textures and various cheats to match what was shot, without having an HDRI from the location. Once I have my treeline texture correct, I just need it to block the sky, and using a texture, an alpha and a light is the fastest way to do it, in RT, if it works. The way the tool seems setup, suggests this should work fine. Texture in texture slot, alpha in alpha slot, light has texture in it where alpha is white, transparent where alpha is black....am I missing something? As I say, this has been my workflow with ramps for years.

[seandunderdale]

I probably will just use a plane and a Vray light material, but Id really like to work out why this method isnt working with a light.

[hermit.crab]

Try using a texture with an alpha channel and plug its Out RGB and Alpha to the respective rectangular light's slots.

[seandunderdale]

Nice, that works perfectly. Thanks Aleksandar. This scene has a tif with transparency plugged into the texture and the out alpha connect, and theres a domelight with a ramp as the env light and its all blending correctly. One other issue, that doesn't matter really, but is there a way to make the texture appear rotated correctly in the viewport display? Its always upside down.

[hermit.crab]

Glad it worked out. Regarding the other issue, we are aware of it (internal bug-tracker id: VMAYA-5515), however, it is Maya related and its fix depends on Autodesk. I'll ask our developers to double-check this though.

[seandunderdale]

Cheer buddy. Honestly I think I've got a form of stockholm syndrome with Maya now. I'm so used to finding workarounds and habits for its weird behavior and bugs that if it was to work the way it should do, Id struggle to use it.

[SonyBoy]

Nothing wrong with putting a texture into the texture slot of course -- that's what it's there for. Based on your image it seemed you were using lights as in-camera cards, which while probably do-able seemed a bit unorthodox to me. Sounds like that isn't the case. If you're looking purely for reflections rather than illumination, I'd still think that geometry rather than lights would be the way to go though...

[seandunderdale]

You're probably right that in most cases geo would make sense, but we are still on 3.6 here, and with a heavy CAD asset, fine tuning the placement is tedious when you move geo and it re-caches RT. Lights work much faster in that respect.