2d export

[jrmobley]

I have refactored the SVG and DXF export into three classes. The Drawing class creates an XY planar projection of a shape and provides the hidden and visible edges. The ExportDXF and ExportSVG classes provide multi-layer export of XY planar shapes to DXF and SVG files respectively.

All b-splines are reduced to at most 3rd degree. B-Splines are converted to poly-bézier curves for SVG export. Conics other than circles and ellipses are exported as b-splines/béziers. Bézier curves are exported to DXF as b-splines. Otherwise edges are exported in their original form.

The interfaces of ExportDXF and ExportSVG are both modeled after features of DXF as exposed by the ezdxf library. I have attempted to make the SVG output match DXF output as closely as possible.

I took the liberty of making some biggish decisions in this PR, so I wanted to get it posted for discussion and feedback.

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: -7.73 ⚠️

Comparison is base (5bf490d) 92.01% compared to head (75b1da5) 84.29%.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #190      +/-   ##
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- Coverage   92.01%   84.29%   -7.73%     
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  Files          13       14       +1     
  Lines        4673     5101     +428     
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  Hits         4300     4300              
- Misses        373      801     +428     

Impacted Files	Coverage Δ
src/build123d/exporters.py	0.00% <0.00%> (ø)

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[gumyr]

This is excellent work, a huge thank you. Please remove "draft" so it can be merged and we can play with it.

The user would do something like:

svg_file = ExportSVG(unit=Unit.MILLIMETER, line_weight=0.5)
svg_file.add_layer(name="template", line_weight=.., line_type=..)
svg_file.add_shape(template_edges, layer="template")
svg_file.add_layer(name="main", ...)
svg_file.add_shape(my_objects, layer="main")
svg_file.write(...)

?
Currently there is a simple cad_objects.export_svg(...) interface, it doesn't even seem worth keeping this.

@jdegenstein you've done a lot of SVG - what do you think?

[jrmobley]

Ok, I'll mark this ready for review.

Here is one of my usage examples:

        svg = ExportSVG(margin=5, line_weight=0.13)
        svg.add_shape(dwg.visible_lines)
        svg.add_layer("hidden", color=ColorIndex.LIGHT_GRAY, line_weight=0.09, line_type=LineType.ISO_DASH_SPACE)
        svg.add_shape(dwg.hidden_lines, layer="hidden")
        svg.write("dev-drawing.svg")

Shapes added without a layer argument are added to the default layer. The default layer properties are supplied you construct the exporter.

Here is how I make a section for export. The exporter expects all topology to be in the XY plane.

with BuildPart() as x:
    Add(pcb)
    Section(m3_plane)
section: Compound = m3_plane.to_local_coords(x.part)

Regarding the cad_objects.export_svg(...) interfaces, you could ditch them or just re-implement them with the new exporters. I'm ambivalent about that one.

[jdegenstein]

Looks very interesting! I haven't tried it yet, but I would like to create e.g. the build123d logo without using inkscape. I want to be able to control line width/color and fill color. Is this possible with the new changes?

[jrmobley]

Looks very interesting! I haven't tried it yet, but I would like to create e.g. the build123d logo without using inkscape. I want to be able to control line width/color and fill color. Is this possible with the new changes?

I'm afraid it isn't really possible right now. With the Drawing in particular, I don't think the underlying OCCT hidden-line removal algorithm maintains or reconstructs any information about faces. So the output has no closed shapes to fill, it's just a line soup. Maybe there is a completely different algorithm available that would be more suitable? Research required.

For 2D sections, it is also currently processed as a line soup, but there does exist the possibility of traversing down the topology tree and organizing the output into fillable shapes. But as the implementation stands currently, no the user cannot get filled output.

Regarding per-line colors and filled output, @gumyr I know you mention this in issue 56, and I was thinking about implementation. The primary obstacle I see is that below the level of Compound in the topology tree, you have to rely upon OCCT to enumerate the child objects, and so you get OCCT objects without the b3d wrappers, so it seems like color assignments would be lost. AFAICT.

[gumyr]

@jrmobley by "you have to rely upon OCCT to enumerate the child objects" is this being done with OCCT methods or edges(). I ask because (in the algebra branch) I've made modifications such that edges() assigns a new topo_parent instance variable (this was done so the parent shape doesn't need to be provided in a fillet). Thus is would be easy to find a parent's color and use that.

[jrmobley]

The exporters right now are using edges() so that topo_parent could enable some stuff. I was picturing a tree traversal like you do in show_topology() in order to keep the structure intact when exporting SVG, but maybe that is overkill?