.

Author: tmcw

README.md

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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](https://github.com/georust/geo/issues/641), 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](https://emscripten.org/docs/compiling/Building-Projects.html#using-libraries).
+  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
+```

build.sh

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+FLAGS=`geos-config --cflags`
+LIBS=`geos-config --clibs`
+
+
+cc $LIBS hello_world.c $FLAGS -o hello_world
+emcc $LIBS hello_world.c $FLAGS -o hello_world

hello_world

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+/* geos_hello_world.c */
+
+#include <stdio.h>  /* for printf */
+#include <stdarg.h> /* for va_list */
+
+/* Only the CAPI header is required */
+#include <geos_c.h>
+
+/*
+* GEOS requires two message handlers to return
+* error and notice message to the calling program.
+*
+*   typedef void(* GEOSMessageHandler) (const char *fmt,...)
+*
+* Here we stub out an example that just prints the
+* messages to stdout.
+*/
+static void
+geos_msg_handler(const char* fmt, ...)
+{
+    va_list ap;
+    va_start(ap, fmt);
+    vprintf (fmt, ap);
+    va_end(ap);
+}
+
+int main()
+{
+    /* Send notice and error messages to the terminal */
+    initGEOS(geos_msg_handler, geos_msg_handler);
+
+    /* Read WKT into geometry object */
+    GEOSWKTReader* reader = GEOSWKTReader_create();
+    GEOSGeometry* geom_a = GEOSWKTReader_read(reader, "POINT(1 1)");
+
+    /* Convert result to WKT */
+    GEOSWKTWriter* writer = GEOSWKTWriter_create();
+    char* wkt = GEOSWKTWriter_write(writer, geom_a);
+    printf("Geometry: %s\n", wkt);
+
+    /* Clean up allocated objects */
+    GEOSWKTReader_destroy(reader);
+    GEOSWKTWriter_destroy(writer);
+    GEOSGeom_destroy(geom_a);
+    GEOSFree(wkt);
+
+    /* Clean up the global context */
+    finishGEOS();
+    return 0;
+}