How to handle index buffer in OpenGL ES 1.1

Question

I want to render a model loaded from an .obj file using OPENGL ES 1.1 for Android. I have vertices, vertice normals and faces. When I render the model using GL10.GL_POINTS the model looks fine:

When I use GL10.GL_TRIANGLES I get a mess of shapes like this:

Here's my drawing method. I tried both glDrawArrays and glDrawElements but got the same results.

public void draw(GL10 gl){
    gl.glEnable(GL10.GL_CULL_FACE);
    gl.glFrontFace(GL10.GL_CCW);
    gl.glCullFace(GL10.GL_BACK);

    gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);
    gl.glVertexPointer(COORDS_PER_VERTEX, GL10.GL_FLOAT, BYTES_PER_VERTEX, m_vertexBuffer);

    gl.glEnableClientState(GL10.GL_NORMAL_ARRAY);
    gl.glNormalPointer(COORDS_PER_VERTEX, BYTES_PER_VERTEX, m_normalBuffer);

    gl.glColor4f(m_color[0], m_color[1], m_color[2], m_color[3]);
    gl.glScalef(0.1f, 0.1f, 0.1f);

    // gl.glDrawArrays(GL10.GL_TRIANGLES, 0, m_numNormals);
    gl.glDrawElements(GL10.GL_TRIANGLES, m_numIndices, GL10.GL_UNSIGNED_SHORT, m_indexBuffer);

    gl.glDisableClientState(GL10.GL_VERTEX_ARRAY);
    gl.glDisableClientState(GL10.GL_NORMAL_ARRAY);
    gl.glDisable(GL10.GL_CULL_FACE);
}

Here are sample lines from the .obj file:

v 1.012781 -1.591947 1.752353
...
vn 0.495193 0.342204 0.798517
...
# same indices within pairs
f 14978//14978 14977//14977 22659//22659
...
# different indices
f 34422//34418 34375//34371 34374//34370

What's interesting about the face lines is that sometimes the pairs of v//vn consist of the same indices and sometimes they don't. Also in total there are 4 normals less than vertices. I suspect this is what's causing the problems. But how would I deal with that? When I use glDrawElements, which indices should I pass?

This is how I initialize my Buffers:

public void setVertices(float[] coordinates, int size){
    final ByteBuffer bb = ByteBuffer.allocateDirect(size * 4);
    bb.order(ByteOrder.nativeOrder());
    m_vertexBuffer = bb.asFloatBuffer();
    m_vertexBuffer.put(coordinates, 0, size);
    m_vertexBuffer.position(0);
    m_numVertices = size / COORDS_PER_VERTEX;
}

public void setNormals(float[] coordinates, int size){
    final ByteBuffer bb = ByteBuffer.allocateDirect(size * 4);
    bb.order(ByteOrder.nativeOrder());
    m_normalBuffer = bb.asFloatBuffer();
    m_normalBuffer.put(coordinates, 0, size);
    m_normalBuffer.position(0);
    m_numNormals = size / COORDS_PER_VERTEX;
}

// array contains vertices and normals in the order read from the .obj file
// ie every even index is a vertex, every odd index is a normal
public void setIndices(int[] array, int size){
    m_numIndices = size / 2;
    final ByteBuffer bb = ByteBuffer.allocateDirect(m_numIndices * 4);
    bb.order(ByteOrder.nativeOrder());
    m_indexBuffer = bb.asIntBuffer();
    for(int i = 0; i < size; i+=2)
        m_indexBuffer.put(array[i]);
    m_indexBuffer.position(0);
}

Can you maybe give me a hint how to initialize and use the index buffer?

EDIT: here's the model: bunny.obj

Answer 1

maybe this will help you i used it to import an .obj file and it worked with a texture and everything, you will have to pick it apart to whats relevant to your project its tied into all these other classes, like the instance of GLGame and GLGraphics are used for file input and getting an instance of GL10, good luck, hope this helps

object loader

public class ObjLoader {
    public static Vertices3 load(GLGame game, String file) {
        InputStream in = null;
        try {
            in = game.getFileIO().readAsset(file);
            List<String> lines = readLines(in);

            float[] vertices = new float[lines.size() * 3];
            float[] normals = new float[lines.size() * 3];
            float[] uv = new float[lines.size() * 2];

            int numVertices = 0;
            int numNormals = 0;
            int numUV = 0;
            int numFaces = 0;

            int[] facesVerts = new int[lines.size() * 3];
            int[] facesNormals = new int[lines.size() * 3];
            int[] facesUV = new int[lines.size() * 3];
            int vertexIndex = 0;
            int normalIndex = 0;
            int uvIndex = 0;
            int faceIndex = 0;

            for (int i = 0; i < lines.size(); i++) {
                String line = lines.get(i);
                if (line.startsWith("v ")) {
                    String[] tokens = line.split("[ ]+");
                    vertices[vertexIndex] = Float.parseFloat(tokens[1]);
                    vertices[vertexIndex + 1] = Float.parseFloat(tokens[2]);
                    vertices[vertexIndex + 2] = Float.parseFloat(tokens[3]);
                    vertexIndex += 3;
                    numVertices++;
                    continue;
                }

                if (line.startsWith("vn ")) {
                    String[] tokens = line.split("[ ]+");
                    normals[normalIndex] = Float.parseFloat(tokens[1]);
                    normals[normalIndex + 1] = Float.parseFloat(tokens[2]);
                    normals[normalIndex + 2] = Float.parseFloat(tokens[3]);
                    normalIndex += 3;
                    numNormals++;
                    continue;
                }

                if (line.startsWith("vt")) {
                    String[] tokens = line.split("[ ]+");
                    uv[uvIndex] = Float.parseFloat(tokens[1]);
                    uv[uvIndex + 1] = Float.parseFloat(tokens[2]);
                    uvIndex += 2;
                    numUV++;
                    continue;
                }

                if (line.startsWith("f ")) {
                    String[] tokens = line.split("[ ]+");

                    String[] parts = tokens[1].split("/");
                    facesVerts[faceIndex] = getIndex(parts[0], numVertices);
                    if (parts.length > 2)
                        facesNormals[faceIndex] = getIndex(parts[2], numNormals);
                    if (parts.length > 1)
                        facesUV[faceIndex] = getIndex(parts[1], numUV);
                    faceIndex++;

                    parts = tokens[2].split("/");
                    facesVerts[faceIndex] = getIndex(parts[0], numVertices);
                    if (parts.length > 2)
                        facesNormals[faceIndex] = getIndex(parts[2], numNormals);
                    if (parts.length > 1)
                        facesUV[faceIndex] = getIndex(parts[1], numUV);
                    faceIndex++;

                    parts = tokens[3].split("/");
                    facesVerts[faceIndex] = getIndex(parts[0], numVertices);
                    if (parts.length > 2)
                        facesNormals[faceIndex] = getIndex(parts[2], numNormals);
                    if (parts.length > 1)
                        facesUV[faceIndex] = getIndex(parts[1], numUV);
                    faceIndex++;
                    numFaces++;
                    continue;
                }
            }

            float[] verts = new float[(numFaces * 3)
                    * (3 + (numNormals > 0 ? 3 : 0) + (numUV > 0 ? 2 : 0))];

            for (int i = 0, vi = 0; i < numFaces * 3; i++) {
                int vertexIdx = facesVerts[i] * 3;
                verts[vi++] = vertices[vertexIdx];
                verts[vi++] = vertices[vertexIdx + 1];
                verts[vi++] = vertices[vertexIdx + 2];

                if (numUV > 0) {
                    int uvIdx = facesUV[i] * 2;
                    verts[vi++] = uv[uvIdx];
                    verts[vi++] = 1 - uv[uvIdx + 1];
                }

                if (numNormals > 0) {
                    int normalIdx = facesNormals[i] * 3;
                    verts[vi++] = normals[normalIdx];
                    verts[vi++] = normals[normalIdx + 1];
                    verts[vi++] = normals[normalIdx + 2];
                }
            }

            Vertices3 model = new Vertices3(game.getGLGraphics(), numFaces * 3,
                    0, false, numUV > 0, numNormals > 0);
            model.setVertices(verts, 0, verts.length);
            return model;
        } catch (Exception ex) {
            throw new RuntimeException("couldn't load '" + file + "'", ex);
        } finally {
            if (in != null)
                try {
                    in.close();
                } catch (Exception ex) {

                }
        }
    }

    static int getIndex(String index, int size) {
        int idx = Integer.parseInt(index);
        if (idx < 0)
            return size + idx;
        else
            return idx - 1;
    }

    static List<String> readLines(InputStream in) throws IOException {
        List<String> lines = new ArrayList<String>();

        BufferedReader reader = new BufferedReader(new InputStreamReader(in));
        String line = null;
        while ((line = reader.readLine()) != null)
            lines.add(line);
        return lines;
    }
}

vertices3

public class Vertices3 {
    final GLGraphics glGraphics;
    final boolean hasColor;
    final boolean hasTexCoords;
    final boolean hasNormals;
    final int vertexSize;
    final IntBuffer vertices;
    final int[] tmpBuffer;
    final ShortBuffer indices;

    public Vertices3(GLGraphics glGraphics, int maxVertices, int maxIndices,
            boolean hasColor, boolean hasTexCoords, boolean hasNormals) {
        this.glGraphics = glGraphics;
        this.hasColor = hasColor;
        this.hasTexCoords = hasTexCoords;
        this.hasNormals = hasNormals;
        this.vertexSize = (3 + (hasColor ? 4 : 0) + (hasTexCoords ? 2 : 0) + (hasNormals ? 3
                : 0)) * 4;
        this.tmpBuffer = new int[maxVertices * vertexSize / 4];

        ByteBuffer buffer = ByteBuffer.allocateDirect(maxVertices * vertexSize);
        buffer.order(ByteOrder.nativeOrder());
        vertices = buffer.asIntBuffer();

        if (maxIndices > 0) {
            buffer = ByteBuffer.allocateDirect(maxIndices * Short.SIZE / 8);
            buffer.order(ByteOrder.nativeOrder());
            indices = buffer.asShortBuffer();
        } else {
            indices = null;
        }
    }

    public void setVertices(float[] vertices, int offset, int length) {
        this.vertices.clear();
        int len = offset + length;
        for (int i = offset, j = 0; i < len; i++, j++)
            tmpBuffer[j] = Float.floatToRawIntBits(vertices[i]);
        this.vertices.put(tmpBuffer, 0, length);
        this.vertices.flip();
    }

    public void setIndices(short[] indices, int offset, int length) {
        this.indices.clear();
        this.indices.put(indices, offset, length);
        this.indices.flip();
    }

    public void bind() {
        GL10 gl = glGraphics.getGL();

        gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);
        vertices.position(0);
        gl.glVertexPointer(3, GL10.GL_FLOAT, vertexSize, vertices);

        if (hasColor) {
            gl.glEnableClientState(GL10.GL_COLOR_ARRAY);
            vertices.position(3);
            gl.glColorPointer(4, GL10.GL_FLOAT, vertexSize, vertices);
        }

        if (hasTexCoords) {
            gl.glEnableClientState(GL10.GL_TEXTURE_COORD_ARRAY);
            vertices.position(hasColor ? 7 : 3);
            gl.glTexCoordPointer(2, GL10.GL_FLOAT, vertexSize, vertices);
        }

        if (hasNormals) {
            gl.glEnableClientState(GL10.GL_NORMAL_ARRAY);
            int offset = 3;
            if (hasColor)
                offset += 4;
            if (hasTexCoords)
                offset += 2;
            vertices.position(offset);
            gl.glNormalPointer(GL10.GL_FLOAT, vertexSize, vertices);
        }
    }

    public void draw(int primitiveType, int offset, int numVertices) {
        GL10 gl = glGraphics.getGL();

        if (indices != null) {
            indices.position(offset);
            gl.glDrawElements(primitiveType, numVertices,
                    GL10.GL_UNSIGNED_SHORT, indices);
        } else {
            gl.glDrawArrays(primitiveType, offset, numVertices);
        }
    }

    public void unbind() {
        GL10 gl = glGraphics.getGL();
        if (hasTexCoords)
            gl.glDisableClientState(GL10.GL_TEXTURE_COORD_ARRAY);

        if (hasColor)
            gl.glDisableClientState(GL10.GL_COLOR_ARRAY);

        if (hasNormals)
            gl.glDisableClientState(GL10.GL_NORMAL_ARRAY);
    }

    public int getNumIndices() {
        return indices.limit();
    }

    public int getNumVertices() {
        return vertices.limit() / (vertexSize / 4);
    }
}