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Fix floating point accuracy issue in triangulation #81

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Jan 25, 2022
Merged

Fix floating point accuracy issue in triangulation #81

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37 changes: 30 additions & 7 deletions src/kernel/topology/faces.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -108,18 +108,41 @@ impl Face {
let outside = aabb.maxs * 2.;

triangles.retain(|triangle| {
for segment in triangle.edges() {
'outer: for segment in triangle.edges() {
let mut inverted_segment = segment;
inverted_segment.swap();

let triangle_segment_is_face_edge = face_as_polygon
.contains(&segment)
|| face_as_polygon.contains(&inverted_segment);

// If the segment is an edge of the face, we don't need
// to take a closer look.
if triangle_segment_is_face_edge {
continue;
//
// We can't use `contains` here, as that compares the
// segments directly, without taking floating point
// accuracy into account.
//
// This is not great. See this issue:
// https://github.com/hannobraun/Fornjot/issues/78
for s in &face_as_polygon {
// This epsilon value is small enough to not mistake
// different vertices as equal, for common use
// cases, while still being a few orders of
// magnitude larger than the differences between
// equal vertices that I've seen so far.
let eps = 1e-12;

let aa = (s.a - segment.a).magnitude();
let bb = (s.b - segment.b).magnitude();
let ab = (s.a - segment.b).magnitude();
let ba = (s.b - segment.a).magnitude();

let segment_is_face_edge = aa < eps && bb < eps;
let segment_is_inverted_face_edge =
ab < eps && ba < eps;

if segment_is_face_edge
|| segment_is_inverted_face_edge
{
continue 'outer;
}
}

// To determine if the edge is within the polygon, we
Expand Down