Android Integration

[farzaa]

Hey there everyone! I'm having a hard time getting Draco to work on an Android device. The documentation says:

To include Draco in an existing or new Android Studio project, reference it from the cmake file of an existing native project that has a minimum SDK version of 18 or higher. The project must support C++11. To add Draco to your project:

I'm not sure what it means to reference Draco from an "existing native project. If someone could please explain the steps on how to get this going that'd be awesome :).

[tomfinegan]

Can you clarify where you're having the problem? Are you starting with a new project, or adding Draco to one which already exists?

For either case the steps on https://github.com/google/draco#android-studio-project-integration still appear to be correct, but I haven't had time to test them lately.

[farzaa]

Hiya. So, I've made a bit of progress. I managed to create a static library (.a) using Android Studio for x86_84 which should work with an x86_84 emulator. \

Here's how I'm doing my decode from within JNI. The line LOGI("%s", "❌ Bad decode in triangular mesh\n"); always runs whenever I try and decode. This means I'm able to load a mesh, but once I begin to decode it it runs into a bit of a snag. This is happening with every mesh I try, including the bunny.ply given in the original readme.

If you could perhaps test out Android and see if its properly decoding a triangular mesh on your end as a sanity check, that'd be awesome. Also, I should mention I get this same behavior when trying to decode a point cloud as well.

But please do let me know if you see anything wrong with the code. Though, its almost a direct copy paste of code from draco_decoder.cc.

Any tips would be greatly appreciated.

Java_com_example_hellolibs_MainActivity_stringFromJNI(JNIEnv *env, jobject thiz) {

    LOGI("%s", "✅ Welcome to Draco by Flynn.");

    std::ifstream input_file("/storage/emulated/0/FLYNN/bunny.drc", std::ios::binary);

    if (!input_file) {
        LOGI("%s", "❌ Input file not found.");
        return;
    } else {
        LOGI("%s", "✅ Opened input file.");
    }

    // Read the file stream into a buffer.
    std::streampos file_size = 0;
    input_file.seekg(0, std::ios::end);
    file_size = input_file.tellg() - file_size;
    input_file.seekg(0, std::ios::beg);
    std::vector<char> data(file_size);
    input_file.read(data.data(), file_size);

    if (data.empty()) {
        LOGI("%s", "❌ Input file was empty");
        return;
    } else {
        LOGI("%s", "✅ Input file was not empty!");
    }

    draco::DecoderBuffer buffer;
    buffer.Init(data.data(), data.size());

    // Decode the input data into a geometry.
    std::unique_ptr<draco::PointCloud> pc;
    draco::Mesh *mesh = nullptr;
    auto type_statusor = draco::Decoder::GetEncodedGeometryType(&buffer);
    if (!type_statusor.ok()) {
        LOGI("%s", "❌ Decoded geometry type is messed up!");
        return;
    }

    LOGI("ANOTHER... %s", type_statusor.status().error_msg());
    const draco::EncodedGeometryType geom_type = type_statusor.value();
    if (geom_type == draco::TRIANGULAR_MESH) {

        draco::Decoder decoder;
        auto statusor = decoder.DecodeMeshFromBuffer(&buffer);
        LOGI("%s", statusor.status().error_msg());
        if (!statusor.ok()) {
            LOGI("%s", "❌ Bad decode in triangular mesh\n");
            return;
        }

        std::unique_ptr<draco::Mesh> in_mesh = std::move(statusor).value();

        if (in_mesh) {
            mesh = in_mesh.get();
            pc = std::move(in_mesh);
        }
    } else if (geom_type == draco::POINT_CLOUD) {
        // Failed to decode it as mesh, so let's try to decode it as a point cloud.
        draco::Decoder decoder;
        auto statusor = decoder.DecodePointCloudFromBuffer(&buffer);
        if (!statusor.ok()) {
            LOGI("%s", "❌ Bad decode in P.C mesh \n");
            return;
        }
        pc = std::move(statusor).value();

    }

    if (pc == nullptr) {
        LOGI("%s", "❌ Failed to decode the input file.\n");
    } else {
        LOGI("%s", "✅ Decoded!");
    }

}

[farzaa]

I've got it working! Here is my project ->

https://github.com/farzaa/DracoPortedToAndroid

Think I should make a PR to throw this in as an example for Android?

[tomfinegan]

I've got it working!

What was the fix?

Think I should make a PR to throw this in as an example for Android?

It depends on what the issue actually was behind the problem. At this point, no, I don't think that's necessary, but I could be convinced otherwise is the underlying issue is a complex issue that reproduces easily and impacts all developers attempting native integration with Draco.

[farzaa]

So for me, the fix was to actually just use the generated static libraries (.a) files and have the JNI call that. To generate the library, I followed the instructions on the repo readme. But, is this how the devs want us to do it? I much rather be able to call the Draco code directly from the JNI and not have to generate the static libraries and than link them to my app project.

[tomfinegan]

You should not need to build the static libraries separately. I think we need some more info in Draco's README.md. In addition to the steps noted for updating the CMakelists.txt currently listed in the README.md, I believe you need to add the following the app's build.gradle (within the cmake child of externalNativeBuild):

cppFlags "-DDRACO_POINT_CLOUD_COMPRESSION_SUPPORTED"
cppFlags "-DDRACO_MESH_COMPRESSION_SUPPORTED"
cppFlags "-DDRACO_STANDARD_EDGEBREAKER_SUPPORTED"
cppFlags "-DDRACO_PREDICTIVE_EDGEBREAKER_SUPPORTED"
arguments "-DANDROID_STL=c++_shared"

After adding the above you should be able to build Draco as part of your project instead of using the libs directly.

[tomfinegan]

https://github.com/google/draco/pull/377 updates README.md.

These aren't needed:

cppFlags "-DDRACO_POINT_CLOUD_COMPRESSION_SUPPORTED"
cppFlags "-DDRACO_MESH_COMPRESSION_SUPPORTED"
cppFlags "-DDRACO_STANDARD_EDGEBREAKER_SUPPORTED"
cppFlags "-DDRACO_PREDICTIVE_EDGEBREAKER_SUPPORTED"
arguments "-DANDROID_STL=c++_shared"

The existing README was nearly correct. It was only missing the ANDROID_STL setting from the cmake child of externalNativeBuild:

arguments "-DANDROID_STL=c++_shared"

With these updates I'm able to build Draco from within Android Studio and use it from a basic test application on my Android device by simply following the instructions in README.md. My test application is essentially a copy/paste of the code from draco_decoder.cc into native-lib.cpp. The only additional steps were related to file system access permissions.

Please feel free to comment or reopen. Closing this for now.