3d Convex Hull #489

geoffder · 2023-07-13T08:25:07Z

This adds a 3d convex hull operation to Manifold. Implementation is a port of what I have in OCADml, which is a port of BOSL2. I've made some effort to get the performance reasonable (for this algorithm anyway, there may be smarter ones out there). From my rough measurement, the vast majority of the time is spent on the DistanceToPlane operation, so I'm not sure what can be wrung out.

I've set it up to try and preserve some properties info, but I'm not too familiar with that API, so I'm hoping that what I've missed can get filled in with review.

codecov · 2023-07-13T08:46:23Z

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.09 ⚠️

Comparison is base (da3f323) 90.35% compared to head (aaca0c8) 90.27%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #489      +/-   ##
==========================================
- Coverage   90.35%   90.27%   -0.09%     
==========================================
  Files          35       35              
  Lines        4396     4410      +14     
==========================================
+ Hits         3972     3981       +9     
- Misses        424      429       +5

Impacted Files	Coverage Δ
src/manifold/include/manifold.h	`100.00% <ø> (ø)`
src/manifold/src/manifold.cpp	`95.63% <100.00%> (+0.29%)`	⬆️

... and 5 files with indirect coverage changes

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src/manifold/src/manifold.cpp

elalish

I guess before we go any further we should figure out the performance of this algorithm. If we're not close to what other libraries achieve, we should probably take a dependency, because our n will tend to be quite large.

src/manifold/src/manifold.cpp

test/manifold_test.cpp

src/manifold/src/manifold.cpp

geoffder · 2023-07-13T15:53:30Z

RE: libraries this one is the top result, and seems like it'd be easy to vendor and use if we want to just go the dependency route. It's an implementation of QuickHull which I believe is better than what I have here. It also supports multithreading but via OMP, maybe forking and adapting it to Manifold's flexible OMP/TBB use via thrust would be worthwhile.

There are a couple papers that say they have something faster than QHull but I just looked at summaries/abstracts last night.

This was a good experience in imperative-izing and general C++ practice anyways 😅.

This is the other article about 3d hull algorithms with example implementations that I meant to link before (deleted wrong paste for 2d).

While I'm listing options, here are some simpler to consume quickhull implementations that I've come across for reference:

geoffder · 2023-07-13T23:35:02Z

I'll go ahead try out the header quickhulls implementations that I linked above on then. Not necessary to start with I don't think, but might be interesting to try out a strategy like described here in this video and article in the future. I'm curious how this and another similar paper I've seen along the way actually play out with the kind of inputs we'd have in Manifold, since many of the benchmarks that are shown off in these things are clouds rather than separate sphere meshes (that are already hollow) for example.

geoffder · 2023-07-14T18:38:01Z

So far out of the non-qhull options, akuuka performs the best, as in it doesn't blow up and OOM my 32GM completely at circularSegments = 1000 (does at 10000) in the basic tictac hull test, but it is capping out the resolution below even that level (the hull output has lower resolution triangles than the input).

I guess I'm going to actually have to try qhull next to see if it has similar limitations.

edit: Actually, when using double rather than float it maintains the resolution at 1000.

At 5000 (2 * 6250038 vertex spheres) it completed in 140s capping out at about 15GB ram.

geoffder · 2023-07-17T00:28:14Z

After trying the above mentioned libs it seems like Akuukka's QuickHull implementation is the way to go, with very few lines of code and CMakeLists.txt required to get it working to boot.

geoffder · 2023-07-17T01:41:24Z

The time to hull I mentioned before was actually an over-estimate since it included the time to get the huge mesh and export it 😅, here is a rough idea of scaling over vertex count.

TEST(Manifold, TictacBench) {
  const float tictacRad = 100;
  const float tictacHeight = 500;
  const float tictacMid = tictacHeight - 2 * tictacRad;
  const std::vector<int> tictacSegs{36,   360,  720,  1000, 2000,
                                    3000, 4000, 5000, 6000};
  for (int seg : tictacSegs) {
    auto sphere = Manifold::Sphere(tictacRad, seg);
    auto spheres = sphere + sphere.Translate({0, 0, tictacMid});
    auto t0 = std::chrono::system_clock::now();
    auto tictac = spheres.Hull();
    double ms = std::chrono::duration_cast<std::chrono::milliseconds>(
                    std::chrono::system_clock::now() - t0)
                    .count();
    std::printf("segs = %i; verts = %i; time = %f\n", seg, spheres.NumVert(),
                ms);
  }
}

segs = 36; verts = 652; time = 9.000000
segs = 360; verts = 64804; time = 154.000000
segs = 720; verts = 259204; time = 696.000000
segs = 1000; verts = 500004; time = 1453.000000
segs = 2000; verts = 2000004; time = 6134.000000
segs = 3000; verts = 4500004; time = 14119.000000
segs = 4000; verts = 8000004; time = 26975.000000
segs = 5000; verts = 12500004; time = 48744.000000
segs = 6000; verts = 18000004; time = 77166.000000

elalish

I like this library you found, thanks!

src/manifold/src/manifold.cpp

elalish · 2023-07-17T05:23:45Z

src/manifold/src/manifold.cpp

+
+Manifold Manifold::Hull() const {
+  auto mesh = GetMeshGL();


So this is to get 1:1 properties to positions? Of course that means we'll get duplicate positions with different properties, so it's going to be basically random which properties end up in the output. Also, it'll be hard to make sense of them without an originalID, since some of those properties might mean different things. Actually it's worse that than: you could end up with a face interpolating UV coordinates into vertex colors or something, since there's no guarantee the verts are from the same input object.

I wonder if we should just remove properties from the Hull entirely and do just geometry for this reason. I can't think of a way to make it sensical otherwise.

I wasn't really sure myself since I don't know much about theesh properties business. I just did it this way to try and preserve properties as you said, hoping that you or pca could point out what more I should be preserving (or not). I did consider triangles ending up with weirdly disparate properties as a possibility, but I don't know/understand what is done with properties during booleans either.

The nice thing about Booleans is we can guarantee a bunch of things: every result triangle is a subset of exactly one input triangle, so it will only every interpolate properties from that triangle. Our decimator is also aware, so it won't merge triangles that don't come from the same original triangle.

Each triangle in a hull is either an input triangle, or a new triangle. I suppose we could try to maintain properties (and faceIDs) for input triangles, but we'd have no choice but to drop them for new triangles. Personally I think it sounds like more trouble than it's worth.

Ok, sounds good 👍. I've stripped out all of the properties stuff and just get the vertices via GetMesh.

src/manifold/src/manifold.cpp

src/third_party/CMakeLists.txt

elalish

Thanks!

src/manifold/src/manifold.cpp

geoffder · 2023-07-17T22:39:41Z

I'll follow up soon with some bindings updates (2d and 3d hull).

Add convex hull methods to Manifold using newly vendored https://github.com/akuukka/quickhull

pca006132 reviewed Jul 13, 2023

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elalish requested changes Jul 13, 2023

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geoffder added 9 commits July 13, 2023 12:55

WIP 3d hull implementation

4818f99

First pass port, unran, untested

4fd9301

Handle remaining dropped triangles

6a23049

WIP debugging

faad606

Basic tictac example working

a488313

Optimize triangle skipping with kept vector

d6cb1f2

Add some basic tests

88fa2f7

Add manifold vector overload

720b8dc

Move forgotten export ifdefs

579b054

geoffder force-pushed the manifold-hull branch from b54fc4b to 579b054 Compare July 13, 2023 19:56

Replace slow impl with Akuukka QuickHull

300b444

quickhull + cxx17 features (try to fix mac build)

5d355ef

elalish requested changes Jul 17, 2023

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geoffder added 6 commits July 16, 2023 23:39

WIP test cases for invalid hull construction

19166d5

Compose rather than boolean for batch Hull

af60a55

Explicit source files for quickhull

8930393

Drop props and return empty on too few pts

f91da6d

Use manifold vec overload for tictac test

935d78f

Add doc comments

37f224d

elalish approved these changes Jul 17, 2023

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Remove uneeded includes

aaca0c8

geoffder merged commit 2f22b92 into elalish:master Jul 18, 2023
22 checks passed

geoffder deleted the manifold-hull branch July 18, 2023 00:12

elalish mentioned this pull request Nov 3, 2023

V2.2.1 #589

Merged

cartesian-theatrics pushed a commit to SovereignShop/manifold that referenced this pull request Mar 11, 2024

3d Convex Hull via Akuukka QuickHull (elalish#489)

73bfe8f

Add convex hull methods to Manifold using newly vendored https://github.com/akuukka/quickhull

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3d Convex Hull #489

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3d Convex Hull #489

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