Save for the occasional reunion concert—which the band asserts they won’t do anymore—Pink Floyd may be long gone, but laser shows built around their music, like the Pink Floyd Laser Spectacular, which plays at the Riverside Theater tonight at 8 p.m., are here to stay. This particular long-running production promises 3-D animation and imagery so impressive that fans don’t need to be drugged out to the point of seeing Syd Barret’s ghost to enjoy it.