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Hanno Braun 2023-08-18 11:11:35 +02:00
parent 6bedfeb841
commit f18424749f
1 changed files with 14 additions and 13 deletions
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27
crates/fj-core/src/algorithms/approx/edge.rs
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@ -43,10 +43,10 @@ impl Approx for (&HalfEdge, &Surface) {
let first = ApproxPoint::new(position_surface, position_global);
let points = {
// We cache approximated `HalfEdge`s using the `GlobalEdge`s they
// reference as the key. That bakes in the undesirable assumption
// that all coincident `HalfEdge`s are also congruent. Let me
// explain.
// We cache approximated `HalfEdge`s using the `Curve`s they
// reference and their boundary on that curve as the key. That bakes
// in the undesirable assumption that all coincident `HalfEdge`s are
// also congruent. Let me explain.
//
// When two `HalfEdge`s are coincident, we need to make sure their
// approximations are identical where they overlap. Otherwise, we'll
@ -54,7 +54,7 @@ impl Approx for (&HalfEdge, &Surface) {
// approximations.
//
// Caching works like this: We check whether there already is a
// cache entry for the `GlobalEdge`. If there isn't, we create the
// cache entry for the curve/boundary. If there isn't, we create the
// 3D approximation from the 2D `HalfEdge`. Next time we check for a
// coincident `HalfEdge`, we'll find the cache and use that, getting
// the exact same 3D approximation, instead of generating a slightly
@ -62,11 +62,11 @@ impl Approx for (&HalfEdge, &Surface) {
//
// So what if we had two coincident `HalfEdge`s that aren't
// congruent? Meaning, they overlap partially, but not fully. Then
// obviously, they wouldn't refer to the same `GlobalEdge`, because
// they are not the same edge, in global coordinates. And since the
// `GlobalEdge` is the key in our cache, those `HalfEdge`s would not
// share an approximation where they overlap, leading to exactly the
// problems that the cache is supposed to avoid.
// obviously, they wouldn't refer to the same combination of curve
// and boundary. And since those are the key in our cache, those
// `HalfEdge`s would not share an approximation where they overlap,
// leading to exactly the problems that the cache is supposed to
// prevent.
//
// As of this writing, it is a documented (but not validated)
// limitation, that coincident `HalfEdge`s must always be congruent.
@ -74,9 +74,10 @@ impl Approx for (&HalfEdge, &Surface) {
// forward, as it is, well, too limiting. This means things here
// will need to change.
//
// What we need here, is more intelligent caching based on `Curve`
// and the edge boundaries, instead of `GlobalEdge`. The cache needs
// to be able to deliver partial results for a given boundary, then
// What we need here, is more intelligent caching, that can reuse
// already cached curve approximations where the boundaries overlap,
// even if those boundaries aren't identical. The cache needs to be
// able to deliver partial results for a given boundary, then
// generating (and caching) the rest of it on the fly.
let cached_approx =
cache.get_edge(half_edge.curve().clone(), half_edge.boundary());