exportSvg doesn't hide edges that are partially visible

[MarcSallent]

This code generates two boxes, one of them crossing the other one. When exporting to SVG with exportSvg, edges that start in a visible area and then intersect the other object are rendered incorrectly.
If they go behind the other object, they are rendered correctly.

Incorrect
from cadquery import cq, Compound
nl = list()
nl.append(cq.Workplane("XY").box(.1, 2, .1, centered=(True, True, True)).val())
nl.append(cq.Workplane("XY").box(2, 1, 1, centered=(True, True, True)).val())
comp = Compound.makeCompound(nl)
cq.Workplane(comp).exportSvg("boxes.svg")

Correct
from cadquery import cq, Compound
nl = list()
nl.append(cq.Workplane("XY").box(.1, 2, .1, centered=(True , True, True)).translate((0,0,-1)).val())
nl.append(cq.Workplane("XY").box(2, 1, 1, centered=(True, True, True)).val())
comp = Compound.makeCompound(nl)
cq.Workplane(comp).exportSvg("boxes2.svg")

Cadquery 2.0 - Python 3.7 - Windows,

[MarcSallent]

To add more info doing Union on the solids works as expected

ra = (cq.Workplane("XY")
      .box(.1, 2, .1, centered=(True , True, True))
      .union(cq.Workplane("XY")
             .box(2, 1, 1, centered=(True, True, True))
             )
      )
ra.exportSvg("boxes3.svg")

[adam-urbanczyk]

This seems to do the trick for me:

from cadquery import cq, Compound
nl = list()
nl.append(cq.Workplane("XY").box(.1, 2, .1, centered=(True, True, True)).val())
nl.append(cq.Workplane("XY").box(2, 1, 1, centered=(True, True, True)).val())
comp = Compound.makeCompound(nl).fuse()

cq.Workplane(comp).exportSvg("boxes.svg")

[adam-urbanczyk]

You want to have internal edges, I assume. Another bool op needs to be used. I think one from here: #449

[MarcSallent]

I will try #449 , but I now understand that an edge crossing a solid through one of their faces (not holes) is not a natural occurence, so maybe this is not actually an issue / worth solving.
Seeing that fuse() or union() perform as expected, I would understand that this issue is closed. (I was avoiding using them to make the export faster)

[adam-urbanczyk]

I'll leave the issue open. It might be good to at leas mention this in the docs.

[njourdane]

I have a similar problem. This code generates glitched svg images:

import cadquery as cq
from cadquery.cq import Workplane as WP

def rod(wp):
    return WP(wp).circle(1).extrude(8)

fig = WP('XY').box(5, 5, 5).add(rod('XY')).add(rod('XZ'))

show_object(fig)
cq.exporters.export(fig, 'figure.svg', opt={
    'projectionDir': (0.3, -0.2, 0.1),
    'showHidden': False
})

CQ-editor VS svg-export:

And if I use union instead add it works as expected:

fig = WP('XY').box(5, 5, 5).union(rod('XY')).union(rod('XZ'))

Does it really make sense to have different behaviors for add and union? Is it for performance purpose?

It might be good to at leas mention this in the docs.

Feel free to use those code / images in the docs if necessary.

[marcus7070]

Does it really make sense to have different behaviors for add and union?

I can see why a user would think they are related methods, but internally they are pretty much unrelated. If you look at the source you can see they do completely different things. It would be very rare you use add.

[adam-urbanczyk]

The solution is to implement #449 and use it before SVG export. The HLR algo does not know what to do with interfering but unrelated solids. It is arguably a very weird use case.