If you guys want my favorite trick for this, it’s to pack a bunch of quads into either a regular or random grid, with two of the points as black vertex color and two as white. The white ones pull towards a world space position, the black ones stay locked to their position Then UV map the “sea” of quads planar, and play a movie back on the material (or pan a fog texture, or whatever). You can even use the luminosity of the shader pixels to decide whether or not to collapse the quads to zero to reduce overdraw on dim parts of the projection. Throw in a little fresnel, use the spline thicken function to make the quads always face the camera… whatever. This trick makes elaborate godrays that either project to a source (think a movie projector) or follow the intricacies of a shader of light coming through a window, or bright crepuscular rays in the distance coming down from clouds. It looks dope and nobody ever uses it for anything 😃 We made movie projectors and hologram projectors with it on a couple different projects.
BTW if you do this on real 3d geometry using dot products (take the dot of a world space position and geo and collapse any facing geo to that point) you can make projected 3d rays that conform perfectly to the shape of the object and its shader, even as it animates. It’s the god tier feature to make holograms look awesome in realtime, and again I never see anyone use it.