Say I have an image blending program written in Python. I want to show the image blending process in a real-time fashion in the frontend while user adjusting the parameters (say several scroll bars), which might require Javascript.
I guess one way to do so is to use libraries mentioned in this similar question: first write a Python class capable of doing the backend job, compile it into JS code and call it from the frontend. Any better ways?
The image manipulation task might be heavier in the future so I write in Python instead of in JS directly.
Depending on the ops you are going to implement, perhaps you could write a parallel implementation of your algorithms using HTML5 Canvas. Then show that in a minimal resolution or provide some way to set up a viewfinder (basically a cropped part of the whole). Once the actual job’s done, show the full result.
You might also want to consider using Node.js for something like this. Essentially this would allow you to use pretty much the same code for both backend and frontend reducing duplication of the algorithms.
You could also try to rethink the way you perform the manipulation. Aviary encourages the users to perform one operation at a time. In addition they provide undo (easy to implement). This kind of scheme would work really well with Canvas.