losing track of colors below Part level

[wjcarpenter]

I know that build123d only allows a single color per Part, which I think is reasonable.

I'm fiddling with some relatively complex code that builds up Part objects in several nested Python layers. I'm OK with extruding individual Part objects out of the lower level Faces (which get their colors in the lower-level logic), but I'm struggling to get build123d to do the color bookkeeping for me. I've tried a lot of variations of Faces added to BuildSketch, sketches wrapped in Compounds, etc. No matter what I've tried, I can't find the color attributes anywhere when I get to the top.

The only way I have found to do this is to keep track of the colored Faces on the side, manually adjusting locations as things are aggregated into other things. I then use that on-the-side bookkeeping to extrude the Faces into Parts. That all works fine, but it obviously sort of ignores all the other work that build123d is doing for me for nested objects.

Is what I'm looking for not there, or have I just not been clever enough to figure it out?

[gumyr]

Color needs to be applied to the individual shapes and doesn't get propagated during any CAD operations. So if you assign a color to a Face and then extrude it into a Solid it won't have a color - at least not currently. The expectation is that once the part is created a color will be assigned to it.

Are you trying to build assemblies of parts and finding that the colors are lost?

[gumyr]

When those faces are combined new faces will be generated so no attempt is made to keep the color as there is no way to know what would be correct. Why not just assign a color once the part is complete?

[wjcarpenter]

Why not just assign a color once the part is complete?

Here's an example of the kind of thing I'm working with (obviously just sample data):

The "R", "G", and "B" are created in lower-level code which has logic to figure out what color they want to be. That gets aggregated with other stuff as the logic moves up the software stack. At the top, I do separate extrusions for each of "R", "G", and "B", each into its own Part. With my on-the-side bookkeeping, I know what colors to assign to those various parts.

When those faces are combined new faces will be generated

In this case, everything is in the same plane, and I'm just using Sketches added to Sketches, so it's not really necessary to generate new faces. I realized that the build123d code probably does that without looking for this special case. But in the top level Sketch topology (before extrusions), the number of faces is exactly the same as the stuff I am keeping track of on the side.

I'm still a little hazy on Sketch vs Shape vs whatever. I know that when I show_topology of that top-level Sketch, it looks like this:

Compound                   at 0x7901c62b8fb0, Center(-0.07574994999999873, 1.1008896230061855, 0.0)
└── Compound               at 0x7901c82780f0, Center(-0.07574994999999873, 1.1008896230061855, 0.0)
    ├── Face               at 0x790211702930, Center(-6.807406575520833, 1.1564527740478519, 0.0)
    │   ├── Wire           at 0x7901c4de5af0, Center(-6.807406575520833, 1.1564527740478519, 0.0)
    │   │   ├── Edge       at 0x7901c43f5e70, Center(-5.024766438802083, -1.4190472259521483, 0.0)
    │   │   │   ├── Vertex at 0x7901c4db5730, Center(-4.646016438802083, -2.525000513712565, 0.0)
 ....

But I guess the bottom line is that I need my separate bookkeeping to do my color stuff. Thanks for your time in answering.

[gumyr]

In this example the “R” would need to be assigned a color after the extrusion once it’s a 3d part. Is there some reason why this must be done in 2d?

[wjcarpenter]

I think I get what you're saying ... if the low-level code could create the Parts and color them and then the higher levels in the software stack keeps track of Parts instead of Sketches, then the colors would travel along with those Parts. That might work (for my use case). I guess the aggregation thing in that case would be Compounds. Let me push that around a little bit in my code.

Thanks!

[wjcarpenter]

That did the trick. Thanks again for the guidance.