Apriltag port to JS using Emscripten.
https://github.com/terraswarm/apriltagJS
This is an attempt at porting the Apriltag visual fiducial system from C to JavaScript using Emscripten.
Sadly, the result is very slow, in part because the Emscripten output is single threaded.
One possible solution is to use lower resolution images.
-
Download Emscripten
-
View the README.md and install. Under Mac:
./emsdk update
./emsdk install latest
./emsdk activate latest
source ./emsdk_env.sh
- Optional: Create a file and compile it:
bash-3.2$ cat main.c
#include <stdio.h>
int main() {
printf("hello, world!\n");
return 0;
}
bash-3.2$ emcc main.c
INFO:root:generating system library: libc.bc... (this will be cached in "/Users/cxh/.emscripten_cache/asmjs/libc.bc" for subsequent builds)
INFO:root: - ok
INFO:root:generating system library: dlmalloc.bc... (this will be cached in "/Users/cxh/.emscripten_cache/asmjs/dlmalloc.bc" for subsequent builds)
INFO:root: - ok
bash-3.2$ node a.out
hello, world!
bash-3.2$
- Build in apriltag:
cd apriltag
make
- Run an example while in the apriltag/ directory:
bash-3.2$ ./example/apriltag_demo ../tag36_11_00586.jpg
loading ../tag36_11_00586.jpg
pjepg: Unknown marker ee at offset 0f56
detection 0: id (36x11)-586 , hamming 0, goodness 0.000, margin 119.062
0 init 0.008000 ms 0.008000 ms
1 blur/sharp 0.001000 ms 0.009000 ms
2 threshold 4.221000 ms 4.230000 ms
3 unionfind 8.689000 ms 12.919000 ms
4 make clusters 3.575000 ms 16.494000 ms
5 fit quads to clusters 22.117000 ms 38.611000 ms
6 quads 1.430000 ms 40.041000 ms
7 decode+refinement 1.049000 ms 41.090000 ms
8 reconcile 0.002000 ms 41.092000 ms
9 debug output 0.002000 ms 41.094000 ms
10 cleanup 0.011000 ms 41.105000 ms
hamm 1 0 0 0 0 0 0 0 0 0 41.097 1
Summary
hamm 1 0 0 0 0 0 0 0 0 0 41.097 1
bash-3.2$
- Use Emscripten to build the JS version:
make apriltags_demo.js
- Run an example:
bash-3.2$ node apriltags_demo.js /working/tag36_11_00586.jpg
Arg: /working/tag36_11_00586.jpg
enlarged memory arrays from 16777216 to 67108864, took 18 ms (has ArrayBuffer.transfer? false)
Warning: Enlarging memory arrays, this is not fast! 16777216,67108864
loading /working/tag36_11_00586.jpg
pjepg: Unknown marker ee at offset 0f56
enlarged memory arrays from 67108864 to 134217728, took 36 ms (has ArrayBuffer.transfer? false)
Warning: Enlarging memory arrays, this is not fast! 67108864,134217728
detection 0: id (36x11)-586 , hamming 0, goodness 0.000, margin 119.062
0 init 1.000000 ms 1.000000 ms
1 blur/sharp 0.000000 ms 1.000000 ms
2 threshold 467.000000 ms 468.000000 ms
3 unionfind 82.000000 ms 550.000000 ms
4 make clusters 467.000000 ms 1017.000000 ms
5 fit quads to clusters 418.000000 ms 1435.000000 ms
6 quads 976.000000 ms 2411.000000 ms
7 decode+refinement 190.000000 ms 2601.000000 ms
8 reconcile 1.000000 ms 2602.000000 ms
9 debug output 2655.000000 ms 5257.000000 ms
10 cleanup 1.000000 ms 5258.000000 ms
hamm 1 0 0 0 0 0 0 0 0 0 5257.000 1
Summary
hamm 1 0 0 0 0 0 0 0 0 0 5257.000 1
bash-3.2$
- Note that the JavaScript version using Emscripten is over 100x slower than the C version.
-
The getopt library was not well supported, so that code is commented out in
apriltag/example/apriltag_demo.c -
To pass files in to code compiled with Emscripten, we need to define use the Emscripten Filesystem API. So, we define a path called
/working, so we add the following to apriltag/example/apriltag_demo.js
#ifdef JS
#include <emscripten.h>
#endif
int main(int argc, char *argv[])
{
#ifdef JS
EM_ASM(
FS.mkdir('/working');
FS.mount(NODEFS, { root: '.' }, '/working');
);
#endif
- Emscripten has pthreads support but it only works with FireFox Nightly channel: "Any code that is compiled with pthreads support enabled will currently only work in the Firefox Nightly channel, since the SharedArrayBuffer specification is still in an experimental research stage before standardization. " So, if apriltag_demo.c is modified so that only one thread is used:
td->nthreads = 1;
For more information, see https://www.icyphy.org/accessors/wiki/Notes/AprilTags