Provide a way to clip lines outside the xyz limits

[moorepants]

Describe the feature you'd like

I created this animation:

If I could clip the ground line at the x limits, then, because I have the animation cyclic, the ground would always look to be moving under the feet.

It turns out that matplotlib3d isn't so easy to clip data outside xyz limits. There was this PR: matplotlib/matplotlib#27349 but if I add axlim_clip=True to the symmeplot line, it works but as expected it removes the whole line.

Maybe if we could set values outside the limits to NaN this would work.

I hit this in this PR: csu-hmc/opty#29

I have faked it with something like:

    scene.add_line([
        origin.locatenew('gl', -0.8*ground.x),
        origin.locatenew('gl', -0.7999*ground.x),
        origin,
        origin.locatenew('gr', 0.7999*ground.x),
        origin.locatenew('gr', 0.8*ground.x),
    ], linestyle='--', axlim_clip=True)

but that does not work either. I want the end points of the line to both move the same way so the dotted aspect of it gives the illusion of the ground moving under the walker.

I struggle to think of a solution for this. I thought I'd share. This has come up with simulating the bicycle too, when you want the scene to move with the bike.

[tjstienstra]

Nice animation 👀

Have you also tried it with more points? E.g.:

scene.add_line([origin.locatenew('gl', s*ground.x) for s in np.linspace(-1, 1)], linestyle='--', axlim_clip=True)

The most optimal solution symmeplot might be able to give for this problem is to automatically add data points on the line where it crosses the limits, but personally I do not like this solution that much either.

[moorepants]

Yes, I suppose if I add many points and the distance decreases between point such that only the tips of the line are clipped, should work.

[moorepants]

Your suggestion worked, but it shrinks the viewable area if you make the line too long, so you have to make it just long enough to span the width of the x limits (but it still shrinks the viewable area). I guess making the points nan outside the limits may be the only true solution.

[moorepants]

That's walking on the moon btw.

[tjstienstra]

I guess making the points nan outside the limits may be the only true solution.

The problem is that you want the line to be moving. I think that the line will be static if you would define it such that it would exactly fit in the view the entire time.

For the bicycle animations, I've chosen to just remove the axes and create my own plane (grid). Maybe I should also add a add_plane feature to symmeplot.

[moorepants]

Yes, but this works fine in 2D matplotlib plots because it ignores all data outside the axis limits. For 3D it seems to have unsuspected behavior relative to 2D plots. You can see in the matplotlib issues and stackoverflow questions that this is just a limitation of the 3D axes and it isn't so easy to define these limits.

So either there is a workaround to make it behave like 2D plots or maybe symmeplot could plot to a 2D axes also.

[tjstienstra]

Yeah, having 2D plots was originally also the idea of #13, which I've just reopened.

[moorepants]

I just noticed that matplotlib 3.10 added 3D clipping: https://matplotlib.org/stable/users/prev_whats_new/whats_new_3.10.0.html#data-in-3d-plots-can-now-be-dynamically-clipped-to-the-axes-view-limits