Validation precision issues with large objects

[IamTheCarl]

Good morning. I started implementing a custom scripting language built around Fornjot. I'll showcase it later when it's more complete.
Two of the key features of this scripting language are that it has type safety revolving around the dimensions of measurements and automatic unit conversion.

The following is an example of how the unit conversion can look. Note that the interpreter is currently configured to convert all inputs to Fornjot as millimeters (this is configurable).

new_region(struct Circle { center = [1m, 2m], radius = 3m })

This would result in Fornjot being fed something similar to this:

Region::circle(
    [1000, 2000],
    3000,
    &mut context.global_resources.fornjot_services,
)

This results in the following validation error:

`Cycle` validation error

Caused by:
	Adjacent `HalfEdge`s are not connected
- End position of first `HalfEdge`: [4000.0, 1999.9999999999993]
- Start position of second `HalfEdge`: [4000.0, 2000.0]
- Distance between vertices: 0.0000000000006821210263296962
- `HalfEdge`s: [
    HalfEdge @ 0x7f0e76dd7010 => HalfEdge {
        path: Circle(
            Circle {
                center: [
                    1000.0,
                    2000.0,
                ],
                a: [
                    3000.0,
                    0.0,
                ],
                b: [
                    0.0,
                    3000.0,
                ],
            },
        ),
        boundary: CurveBoundary {
            inner: [
                [
                    0.0,
                ],
                [
                    6.283185307179586,
                ],
            ],
        },
        curve: Curve @ 0x7f0e481a34a0 => Curve,
        start_vertex: Vertex @ 0x7f0e481a77f0 => Vertex,
    },
    HalfEdge @ 0x7f0e76dd7010 => HalfEdge {
        path: Circle(
            Circle {
                center: [
                    1000.0,
                    2000.0,
                ],
                a: [
                    3000.0,
                    0.0,
                ],
                b: [
                    0.0,
                    3000.0,
                ],
            },
        ),
        boundary: CurveBoundary {
            inner: [
                [
                    0.0,
                ],
                [
                    6.283185307179586,
                ],
            ],
        },
        curve: Curve @ 0x7f0e481a34a0 => Curve,
        start_vertex: Vertex @ 0x7f0e481a77f0 => Vertex,
    },
]

The statement 1999.9999999999993 != 2000.0 is true, so it makes sense we got this failure. I can probably just setup my scripting language to preset this as a warning rather than a hard error, especially for how unrealistic of a situation this is (imagine that big of a 3D printer). But I do think it would be bad to get engineers into the habit of ignoring warnings, so I think it's best to fix false positives.

Could we possibly set an epsilon for comparisons in validation? We can default it to 0.0 and if the engineer is aware that they are making a massive unit conversion like this, they could set the epsilon to be reasonably large.

[hannobraun]

Good morning. I started implementing a custom scripting language built around Fornjot. I'll showcase it later when it's more complete.

Sounds awesome! Looking forward to seeing it!

Could we possibly set an epsilon for comparisons in validation? We can default it to 0.0 and if the engineer is aware that they are making a massive unit conversion like this, they could set the epsilon to be reasonably large.

We can! Here:

fornjot/crates/fj-core/src/core.rs

Lines 22 to 26 in fb6a21b

	/// Construct an instance of `Instance`, using the provided configuration
	pub fn with_validation_config(config: ValidationConfig) -> Self {
	let layers = Layers::with_validation_config(config);
	Self { layers }
	}

This configuration has existed since forever, but it has only recently been exposed through Services (see #2060, #2150). This is not in a release yet.

I'm going to close this issue, as I think this has been addressed. If you have suggestions for specific improvements (like better default values, or maybe automatic adjustment of the settings in some way), feel free to open another issue or pull request!

(I don't know exactly when the next release, which will include the new API, will be out. I hope that I can get to it very soon, but there are a few other items on my list that I have to address first.)

[IamTheCarl]

Ah perfect! That would explain why I didn't find it, as I've been using the release on crates.io assuming it would be just a smidge more stable.

I'll update my scripting language to be able to configure the validation when that feature is ready.