Add `align_z` argument to pack() Method.

[roman-dvorak]

Hi,

I've added a new argument align_z to the pack() method. When you enable this, it aligns all objects to the same Z axis.

Motivation and Context

I made this change to help with preparing print plates for 3D printing (set of multiple 3D bodies). The current pack() method only arranges objects in the X and Y coordinates. With the new align_z option, it becomes much easier to prepare objects for printing without needing to adjust them by a slicer.

How Has This Been Tested?

I did some manual testing to make sure the objects align correctly in the Z axis. See following images:

Without z_align (default)

parts = [box, lid]
p = pack(parts, padding=5, align_z=False)
show(p, reset_camera=Camera.KEEP)

With z_align

parts = [box, lid]
p = pack(parts, padding=5, align_z=True)
show(p, reset_camera=Camera.KEEP)

Thank you!

[gumyr]

The original implementation didn't have the complete docstring - would you add the following (or with any improvements you can think of) to the pack function?

    """Pack objects in a squarish area in Plane.XY.

    Args:
        objects (Collection[Shape]): objects to arrange
        padding (float): space between objects
        align_z (bool, optional): align shape bottoms to Plane.XY. Defaults to False.

    Returns:
        Collection[Shape]: rearranged objects
    """

Thanks for the submission!

[roman-dvorak]

Thanks for the comment. I added it as you wrote it, I have no problem with it and it is correct. Thanks for the help.

I would also like to expand the documentation because the mention of pack function is quite hidden in between 'tips'. I would probably look for such information in the 'assemblies' section. So I would do that in a separate page and additional PR. Do you have any suggestions on where to place it in the documentation?

[gumyr]

Knowing where folks look for stuff is on of the difficult parts of writing good documentation so if you think you'd look in Assemblies I'm okay with that. Maybe a reference in the 3D exporters section would be helpful as well if the next step is to 3D print their objects?

I've merged the PR - thanks again!