Exposing nv.saveScene on the python side

[kolibril13]

As @alexisthual suggested in today's meeting, it would be nice to expose nv.saveScene in order to generate static iamges.
Here's an example on how nv.saveScene is used in niivue:
https://github.com/niivue/ipyniivue-experimental/blob/main/original_gallery.md#color-maps-for-voxels

[kolibril13]

Just investigated this issue a bit:

Python

class AnyNiivue(OptionsMixin, anywidget.AnyWidget):
    _save_scene = t.Bool(False).tag(sync=True)

    def save_scene(self):
        """Saves the current scene to a file"""
        self._save_scene = True

In widget.js

model.on("change:_save_scene", () => {
  nv.saveScene();
});

in notebook:

nv.save_scene()

This does work, but only once, as _save_scene is not being reset to False.
After nv.saveScene(); is called, a pop-up window opens where one can define the filename.

Alternatively, there is also an option to directly pass a file name like this:
nv1.saveScene("ScreenShot.png"); which could be also be implemented on the python side.

I guess the best approach here is to have a JSON traitlet like this
_save_scene_as = t.Dict({"name": "screenshot.png", "counter": 1}).tag(sync=True)

[AnthonyAndroulakis]

Just curious, is there a reason why sending custom messages from py -> ts isn't being used for this purpose?

For example, to implement nv.save_scene, one could make these changes:

src/ipyniivue/_widget.py:

class NiiVue(OptionsMixin, anywidget.AnyWidget):
    # ...

    def save_scene(self, filename: str = "screenshot.png"):
        """Send a message to the frontend to save the scene with the given filename.
        
        Parameters
        ----------
        filename : str
            The filename to save the scene to.
        """
        self.send({
            'type': 'save_scene',
            'data': filename
        })

src/js/widget.ts:

export default {
    async render({ model, el }: { model: Model; el: HTMLElement }) {
        // ...

        // Handle custom messages from the backend
        model.on("msg:custom", (payload: {type: string, data: any}) => {
            const { type, data } = payload;
            switch (type) { 
                case "save_scene":
                    nv.saveScene(data);
                    break;
            }
        });

And then, just use the save scene function nv.save_scene()

[christian-oreilly]

Probably because @kolibril13 was trying to address this issue it using the AnyWidget philosophy. The approach you propose is closer to the approach iPyNiiVue was using before the switch to AnyWidget. I would normally be hesitant to go down that road because of all the synchronization issues we had with that approach but it might work well for this specific functionality. Worth trying. Thanks for the suggestion @AnthonyAndroulakis