geos-wasm

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geos/wasm

GEOS and WebAssembly.

Braindump:

I don't think WebAssembly will constitute a big performance advantage for geographical operations. However, what I do want is battle-tested geometry operations. I love Turf, and continue to contribute to Turf, but a lot of Turf's geometry algorithms are implemented from scratch and aren't nearly as robust as GEOS.

Then Turf uses JSTS for a few of its operations. JSTS - JavaScript port of JTS, which is a port of GEOS - has gotten a lot better. Maybe JSTS is the real best option: it gives roughly the code of GEOS, albeit removed two steps from the original, but doesn't have the full serialization cost of a WASM library.

That said, JSTS is large - we've been trying to remove it from Turf for years and years, and it's not exactly the same set of bugs as GEOS. If I have bugs, I want all of the GEOS things to have bugs! And the roaring success of, say, Shapely, indicates that GEOS's level of bugs is pretty tolerable.

So, the goal of GEOS/WASM is that maybe:

• We can get the same features/bugs as GEOS, with fewer steps to the source than JSTS.
• We can just use GEOS for a lot of stuff.
• Maybe it'll be fast, or small? I don't really know, this is all TBD. I've tinkered with WebAssembly but don't know that much about it.

Other routes

• Maybe rust-geo is robust? But it doesn't have buffering, so probably a no-go.

Implementation options

• Emscripten: oldest and most established option.
• Zig: I like Zig, and maybe this would make the toolchain simpler, and I'd much prefer to write Zig than C or C++. But on the other hand, maybe it'd make the process way less documented.
• Clang: looks like it does WASM directly, too. Looks like Emscripten uses LLVM's native support now.

Notes

Okay, so step one is as painful as expected. Getting the basic GEOS example to compile using any tool is hard. I can't get it compiled with Zig, Emscripten or cc. It's because of import paths and stuff. I haven't messed with C in ages.

Looks like there are other people compiling GEOS as a prereq for other stuff.

• https://github.com/bugra9/gdal3.js

Okay, so far seeing:

• I'll need to compile GEOS first, then compile the bindings per the docs. Trying to compile GEOS separately isn't working yet.

CXXFLAGS="-fexceptions -DRENAME_INTERNAL_LIBTIFF_SYMBOLS -s ERROR_ON_UNDEFINED_SYMBOLS=0" CFLAGS=" -fexceptions -DRENAME_INTERNAL_LIBTIFF_SYMBOLS -s ERROR_ON_UNDEFINED_SYMBOLS=0" emconfigure ./configure --enable-shared=no --disable-inline

• spl.js looks great. Doesn't compile cleanly for me - missing libcharset.a. But still, good to learn from.