What is the correct vector input for a texture connected to a Cycles lamp so that I can make a projector-like textured light?
I am trying to make an projector-like effect with a textured light in Cycles, currently trying it out with a Spot type of lamp, but I am open to any solution involving other lamp types if they work correctly.
The problem is that whatever vector input I use, the texture is always projected downwards, towards the global $-Z$ axis in scene world space, no matter where I point my spot light. I would like to have the texture always project "forward" towards the the direction the spot light is pointing, in the local $-Z$ axis.
The plan would then be to use this spot at several places in my scene, pointing at different directions, and as it currently stands I would have to have a different node setup for each spot instance, manually compensating for each unique rotation in the scene, which would quickly become unpractical.
I have searched around the internet and I am currently using a solution similar to the one on this BSE question.
Is there any better method, perhaps involving some funky Vector Math, or is this not currently supported?