example of compiling geos to JS because why not

geos-voronoi-in-js.c

/*
  To compile:
  first, get a version of geos and put it in `geos` relative path. then...
  
  cd geos
  emconfigure ./configure
  emmake make
  cd ..
  emcc \
    -s EXPORTED_FUNCTIONS='["_get_voronoi"]' \
    -s ASSERTIONS=2 \
    -s DEMANGLE_SUPPORT=1 \
    src/example.c \
    -lgeos_c \
    -Lgeos/capi/.libs/ \
    -Igeos/capi/ \
    -Igeos/include \
    -lgeos \
    -Lgeos/src/.libs/
*/
#include <geos_c.h>
#include <stdio.h>
#include <stdlib.h>
#include <emscripten.h>

char* get_voronoi() {
  initGEOS( (GEOSMessageHandler) printf, (GEOSMessageHandler) printf);

  // 2 points with dimension, 2.
  int size = 100;
  GEOSCoordSequence *inputSequence = GEOSCoordSeq_create(size, 2);
  if (inputSequence == NULL) {
    printf("unable to initialize coordinate. Exiting...\n");
    exit(1);
  }

  for (int i = 0; i < size; i++) {
    GEOSCoordSeq_setX(inputSequence, i, emscripten_random() * 10);
    GEOSCoordSeq_setY(inputSequence, i, emscripten_random() * 10);
  }

  GEOSGeometry *geometry = GEOSGeom_createLineString(inputSequence);
  if (geometry == NULL) {
    printf("geometry is null\n");
    exit(1);
  }
  GEOSGeometry *envelope = NULL;
  double tolerance = 0.0;
  int onlyEdges = 0;
  GEOSGeometry* voronoi = GEOSVoronoiDiagram(
    geometry,
    envelope,
    tolerance,
    onlyEdges
  );
  if (voronoi == NULL) {
    printf("unable to compute voronoi\n");
  }
  GEOSWKTWriter* wktWriter = GEOSWKTWriter_create();
  char *wkt = GEOSWKTWriter_write(wktWriter, voronoi);
  GEOSWKTWriter_destroy(wktWriter);
  wktWriter = NULL;
  finishGEOS();
  return wkt;
}