Using glDrawElements does not draw my .obj file - c++

Question

I am trying to correctly import an .OBJ file from 3ds Max. I got this working using glBegin() & glEnd() from a previous question on here, but had really poor performance obviously, so I am trying to use glDrawElements now.
I am importing a chessboard, its game pieces, etc. The board, each game piece, and each square on the board is stored in a struct GroupObject. The way I store the data is like this:
struct Vertex
{
float position[3];
float texCoord[2];
float normal[3];
float tangent[4];
float bitangent[3];
};
struct Material
{
float ambient[4];
float diffuse[4];
float specular[4];
float shininess; // [0 = min shininess, 1 = max shininess]
float alpha; // [0 = fully transparent, 1 = fully opaque]
std::string name;
std::string colorMapFilename;
std::string bumpMapFilename;
std::vector<int> indices;
int id;
};
//A chess piece or square
struct GroupObject
{
std::vector<Material *> materials;
std::string objectName;
std::string groupName;
int index;
};
All vertices are triangles, so there are always 3 points. When I am looping through the faces f section in the obj file, I store the v0, v1, & v2 in the Material->indices. (I am doing v[0-2] - 1 to account for obj files being 1-based and my vectors being 0-based.
So when I get to the render method, I am trying to loop through every object, which loops through every material attached to that object. I set the material information and try and use glDrawElements. However, the screen is black. I was able to draw the model just fine when I looped through each distinct material with all the indices associated with that material, and it drew the model fine. This time around, so I can use the stencil buffer for selecting GroupObjects, I changed up the loop, but the screen is black.
UPDATE
Replaced original render loop with current one and screenshot of it's result
Here is my render loop. The only thing I changed was the for loop(s) so they go through each object, and each material in the object in turn.
void GLEngine::drawModel()
{
ModelTextures::const_iterator iter;
GLuint texture = 0;
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
// Vertex arrays setup
glEnableClientState( GL_VERTEX_ARRAY );
glVertexPointer(3, GL_FLOAT, model.getVertexSize(), model.getVertexBuffer()->position);
glEnableClientState( GL_NORMAL_ARRAY );
glNormalPointer(GL_FLOAT, model.getVertexSize(), model.getVertexBuffer()->normal);
glClientActiveTexture( GL_TEXTURE0 );
glEnableClientState( GL_TEXTURE_COORD_ARRAY );
glTexCoordPointer(2, GL_FLOAT, model.getVertexSize(), model.getVertexBuffer()->texCoord);
glUseProgram(blinnPhongShader);
objects = model.getObjects();
// Loop through objects...
for( int i=0 ; i < objects.size(); ++i )
{
ModelOBJ::GroupObject *object = objects[i];
// Loop through materials used by object...
for( int j=0 ; j<object->materials.size() ; ++j )
{
ModelOBJ::Material *pMaterial = object->materials[j];
glMaterialfv(GL_FRONT_AND_BACK, GL_AMBIENT, pMaterial->ambient);
glMaterialfv(GL_FRONT_AND_BACK, GL_DIFFUSE, pMaterial->diffuse);
glMaterialfv(GL_FRONT_AND_BACK, GL_SPECULAR, pMaterial->specular);
glMaterialf(GL_FRONT_AND_BACK, GL_SHININESS, pMaterial->shininess * 128.0f);
if (pMaterial->bumpMapFilename.empty())
{
//Bind the color map texture.
texture = nullTexture;
if (enableTextures)
{
iter = modelTextures.find(pMaterial->colorMapFilename);
if (iter != modelTextures.end())
texture = iter->second;
}
glActiveTexture(GL_TEXTURE0);
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, texture);
//Update shader parameters.
glUniform1i(glGetUniformLocation(
blinnPhongShader, "colorMap"), 0);
glUniform1f(glGetUniformLocation(
blinnPhongShader, "materialAlpha"), pMaterial->alpha);
}
//glDrawElements( GL_TRIANGLES, pMaterial->triangleCount * 3, GL_UNSIGNED_INT, &pMaterial->indices.front() );
glDrawElements( GL_TRIANGLES, pMaterial->triangleCount * 3, GL_UNSIGNED_INT, model.getIndexBuffer() + pMaterial->startIndex );
}
}
glDisableClientState(GL_NORMAL_ARRAY);
glDisableClientState(GL_TEXTURE_COORD_ARRAY);
glDisableClientState(GL_VERTEX_ARRAY);
glBindTexture(GL_TEXTURE_2D, 0);
glUseProgram(0);
glDisable(GL_BLEND);
}
Here is what the above method draws:
http://img844.imageshack.us/img844/3793/chess4.png
I don't know what I am missing that's important. If it's also helpful, here is where I read a 'f' face line and store the info in the obj importer in the pMaterial->indices.
else if (sscanf(buffer, "%d/%d/%d", &v[0], &vt[0], &vn[0]) == 3) // v/vt/vn
{
fscanf(pFile, "%d/%d/%d", &v[1], &vt[1], &vn[1]);
fscanf(pFile, "%d/%d/%d", &v[2], &vt[2], &vn[2]);
v[0] = (v[0] < 0) ? v[0] + numVertices - 1 : v[0] - 1;
v[1] = (v[1] < 0) ? v[1] + numVertices - 1 : v[1] - 1;
v[2] = (v[2] < 0) ? v[2] + numVertices - 1 : v[2] - 1;
currentMaterial->indices.push_back(v[0]);
currentMaterial->indices.push_back(v[1]);
currentMaterial->indices.push_back(v[2]);
UPDATE 2
Current output: http://img337.imageshack.us/img337/860/chess4s.png

Answer 1

I was able to fix the model with the following code
glDrawElements( GL_TRIANGLES, pMaterial->triangleCount * 3, GL_UNSIGNED_INT, model.getIndexBuffer() + pMaterial->startIndex );
When I was done importing the model, I went through running a triangleCount & set the startIndex like so. This was my solution:
for (int i = 0; i < static_cast<int>(m_attributeBuffer.size()); i++)
{
if (m_attributeBuffer[i] != materialId)
{
materialId = m_attributeBuffer[i];
++numMaterials;
}
}
// Allocate memory for the materials and reset counters.
m_numberOfObjectMaterials = numMaterials;
m_materials.resize(m_numberOfObjectMaterials);
numMaterials = 0;
materialId = -1;
// Build the meshes. One mesh for each unique material.
for (int i = 0; i < static_cast<int>(m_attributeBuffer.size()); i++)
{
if (m_attributeBuffer[i] != materialId)
{
materialId = m_attributeBuffer[i];
m = m_ObjectMaterials[materialId];
m->startIndex = i * 3;
m->triangleCount = 0;
++m->triangleCount;
}
else
{
++m->triangleCount;
}
}