How to load and display .obj file in Android with OpenGL-ES 2

Question

I am trying to load an .obj file into my Android application and display it using OpenGL 2.

You can find the file here: EDIT: I removed the file, you can use any .obj file that contains the values mentiones below for testing.

There are a lot of similar questions on stackoverflow but I did not find a simple solution that does not require some large library.

The file only contains the following value types:

• g
• v
• vt
• vn
• f

I tried libgdx, which worked ok, but it is a bit overkill for what I need.

I tried the oObjLoader https://github.com/seanrowens/oObjLoader without the LWJGL. The parsing seems to work, but how can I display the values in a simple scene?

The next step is to attach an image as a texture to the object. But for now I would be happy to display the file as it is.

I am open to different solutions like pre-converting the file, because it will only be this one ever within the application.

Thanks!

Status update Basic loading and displaying works now, as shown in my own answer.

Answer 1

I ended up writing a new parser, it can be used like this to build FloatBuffers to use in your Renderer:

ObjLoader objLoader = new ObjLoader(context, "Mug.obj");

numFaces = objLoader.numFaces;

// Initialize the buffers.
positions = ByteBuffer.allocateDirect(objLoader.positions.length * mBytesPerFloat)
        .order(ByteOrder.nativeOrder()).asFloatBuffer();
positions.put(objLoader.positions).position(0);

normals = ByteBuffer.allocateDirect(objLoader.normals.length * mBytesPerFloat)
        .order(ByteOrder.nativeOrder()).asFloatBuffer();
normals.put(objLoader.normals).position(0);

textureCoordinates = ByteBuffer.allocateDirect(objLoader.textureCoordinates.length * mBytesPerFloat)
        .order(ByteOrder.nativeOrder()).asFloatBuffer();
textureCoordinates.put(objLoader.textureCoordinates).position(0);

and here's the parser:

public final class ObjLoader {

    public final int numFaces;

    public final float[] normals;
    public final float[] textureCoordinates;
    public final float[] positions;

    public ObjLoader(Context context, String file) {

        Vector<Float> vertices = new Vector<>();
        Vector<Float> normals = new Vector<>();
        Vector<Float> textures = new Vector<>();
        Vector<String> faces = new Vector<>();

        BufferedReader reader = null;
        try {
            InputStreamReader in = new InputStreamReader(context.getAssets().open(file));
            reader = new BufferedReader(in);

            // read file until EOF
            String line;
            while ((line = reader.readLine()) != null) {
                String[] parts = line.split(" ");
                switch (parts[0]) {
                    case "v":
                        // vertices
                        vertices.add(Float.valueOf(parts[1]));
                        vertices.add(Float.valueOf(parts[2]));
                        vertices.add(Float.valueOf(parts[3]));
                        break;
                    case "vt":
                        // textures
                        textures.add(Float.valueOf(parts[1]));
                        textures.add(Float.valueOf(parts[2]));
                        break;
                    case "vn":
                        // normals
                        normals.add(Float.valueOf(parts[1]));
                        normals.add(Float.valueOf(parts[2]));
                        normals.add(Float.valueOf(parts[3]));
                        break;
                    case "f":
                        // faces: vertex/texture/normal
                        faces.add(parts[1]);
                        faces.add(parts[2]);
                        faces.add(parts[3]);
                        break;
                }
            }
        } catch (IOException e) {
            // cannot load or read file
        } finally {
            if (reader != null) {
                try {
                    reader.close();
                } catch (IOException e) {
                    //log the exception
                }
            }
        }

        numFaces = faces.size();
        this.normals = new float[numFaces * 3];
        textureCoordinates = new float[numFaces * 2];
        positions = new float[numFaces * 3];
        int positionIndex = 0;
        int normalIndex = 0;
        int textureIndex = 0;
        for (String face : faces) {
            String[] parts = face.split("/");

            int index = 3 * (Short.valueOf(parts[0]) - 1);
            positions[positionIndex++] = vertices.get(index++);
            positions[positionIndex++] = vertices.get(index++);
            positions[positionIndex++] = vertices.get(index);

            index = 2 * (Short.valueOf(parts[1]) - 1);
            textureCoordinates[normalIndex++] = textures.get(index++);
            // NOTE: Bitmap gets y-inverted
            textureCoordinates[normalIndex++] = 1 - textures.get(index);

            index = 3 * (Short.valueOf(parts[2]) - 1);
            this.normals[textureIndex++] = normals.get(index++);
            this.normals[textureIndex++] = normals.get(index++);
            this.normals[textureIndex++] = normals.get(index);
        }
    }
}