Am I right in thinking that when reading a trajectory (e.g. .dcd file), all requested frames from that trajectory are first read in, after which the "coordset" command can be used to work with the trajectory? I am reading frames from an RMF file (using the RMF plugin, the "rmf readtraj" command) which is quite slow, perhaps a second per frame - because RMF stores local coordinates which must be transformed to make the global coordinates ChimeraX is using. So if the user asks to read 100 frames, ChimeraX becomes unresponsive for ~100s, which is not a great user experience. One possible solution would be to read the 100 frames "lazily", e.g. just create 100 copies of the active coordset, then when the user writes "coordset #1 N" for the first time or scrolls to frame N with "coordset slider", read in frame N from the RMF file and overwrite coordset N. That way there would be a 1s delay only the first time that frame is shown. Is this possible? I see there is an "active coordset changed" trigger - perhaps I could attach to that? Alternatively, is there an API for tools to run long-running processes in the background so that the user can work on other things in the meantime, or cancel it if it takes too long? Ben -- ben@salilab.org https://salilab.org/~ben/ "It is a capital mistake to theorize before one has data." - Sir Arthur Conan Doyle