Update zoom handling to call update method

[jeromeetienne]

add .update() in_scroll function, thus the caller can know if the camera zoom moved.

Similar to the on_motion() function

It is useful when the caller is processing depending on the distance-to-camera for examples

[rougier]

But the zoom implementation on matplotlib is a trick. I modify viewport limits (instead of -1/+1 set it to -1+delta/+1+delta. This avoids to recompute everything (it works only for zoom). Said differrently, this is a fake camera zoom but good enough.

There is not implementation of an actual camera zoom in the matplotlib implementation even though all necessary functions are here.

[jeromeetienne]

@rougier the camera.zoom is changing appropriatly, meaning it goes from .zoom_min to .zoom_max

so it provides valid z coordinates which can used in the .update() function to compute the size of Points for examples

Or to change the alpha of a color to simulate a fog

Currently the caller can not be notified when the zoom is changing, thus it can not update the point size or the color alpha.

[jeromeetienne]

If you prefere i can provide a PR which has .update() functions per event type ? scroll/click/press/motion

like you did here 😃

[rougier]

The points 3D example does just that.

[jeromeetienne]

@rougier cest ok si je backport la camera de gsp examples ici ?

[rougier]

I did not realize I was on matplotlib-3d repository. Why do you want to change here (instead of GSP) ?

[jeromeetienne]

@rougier im using this library