Exception at glDrawElements - c++

Question

I'm trying to load a model into my project and I get an exception at glDrawElements.
I read the model file (.nfg), and retain the vertices and indices into vectors, and I use Vertex Buffer Object to bind my model.
I tried this:
I modified the fourth parameter from (GLvoid*)(sizeof(Vector3) * x)
to (GLvoid*)(offset(Vertex, attribute)), but didn't do anything (in the link, the problem was that he was sending memory address in the 4th parameter, and I thought maybe I was sending the wrong parameter to the wrong attribute, which still, would be a problem when actually showing the model).
I'm using OpenGL ES 2.0 and I'm not doing this project for neither Android or iOS; currently working in Visual Studio 2013 on Windows 8.1
The model loader:
void loadModelNfg(const std::string &filename,
GLuint &vbo, GLuint &ibo, GLuint &num, Shaders shaders){
// put here the verteces and indices from the file
std::vector<Vertex> vertices;
std::vector<GLushort> indices;
_loadModelNfg(filename, vertices, indices);
std::cout << "Mesh Loader: loaded file: " << filename << "\n";
// creates OpenGL objects necessary for drawing
GLuint gl_vertex_buffer_object, gl_index_buffer_object;
// vertex buffer object -> object in which to keep the vertices
glGenBuffers(1, &gl_vertex_buffer_object);
glBindBuffer(GL_ARRAY_BUFFER, gl_vertex_buffer_object);
glBufferData(GL_ARRAY_BUFFER, vertices.size() * sizeof(Vertex),
&vertices[0], GL_STATIC_DRAW);
glBindBuffer(GL_ARRAY_BUFFER, 0);
// index buffer object -> object in which to keep the indices
glGenBuffers(1, &gl_index_buffer_object);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, gl_index_buffer_object);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, indices.size() * sizeof(GLushort),
&indices[0], GL_STATIC_DRAW);
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
vbo = gl_vertex_buffer_object;
ibo = gl_index_buffer_object;
num = indices.size();
}
Calling the previous function:
// for now, global variables:
GLuint vbo, ibo, num;
Shader myShaders;
int Init ( ESContext* esContext ) {
glClearColor ( 0.0f, 0.0f, 0.0f, 0.0f );
// this one works: tried with a triangle
int ret = myShaders.Init("../Resources/Shaders/TriangleShaderVS.vs",
"../Resources/Shaders/TriangleShaderFS.fs");
if (ret == 0)
loadModelNfg("../../ResourcesPacket/Models/Bila.nfg", vbo, ibo, num, myShaders);
return ret;
}
Drawing the model:
void Draw(ESContext* esContext) {
Matrix world;
world.SetIdentity();
Matrix view = c.getView();
Matrix persp = c.getPerspective();
Matrix trans = world * view *persp;
glClear(GL_COLOR_BUFFER_BIT);
glUseProgram(myShaders.program);
glBindBuffer(GL_ARRAY_BUFFER, vbo);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ibo);
if (myShaders.positionAttribute != -1) {
glEnableVertexAttribArray(myShaders.positionAttribute);
glVertexAttribPointer(myShaders.positionAttribute, 3, GL_FLOAT,
GL_FALSE, sizeof(Vertex), (GLvoid*)(offsetof(Vertex, pos)));
}
if (myShaders.normalAttribute != -1) {
glEnableVertexAttribArray(myShaders.normalAttribute);
glVertexAttribPointer(myShaders.normalAttribute, 3, GL_FLOAT,
GL_FALSE, sizeof(Vertex), (GLvoid*)(offsetof(Vertex, norm)));
}
if (myShaders.binormalAttribute != -1) {
glEnableVertexAttribArray(myShaders.binormalAttribute);
glVertexAttribPointer(myShaders.binormalAttribute, 3, GL_FLOAT,
GL_FALSE, sizeof(Vertex), (GLvoid*)(offsetof(Vertex, binorm)));
}
if (myShaders.tangentAttribute != -1) {
glEnableVertexAttribArray(myShaders.tangentAttribute);
glVertexAttribPointer(myShaders.tangentAttribute, 3, GL_FLOAT,
GL_FALSE, sizeof(Vertex), (GLvoid*)(offsetof(Vertex, tgt)));
}
if (myShaders.texcoordAttribute != -1) {
glEnableVertexAttribArray(myShaders.texcoordAttribute);
glVertexAttribPointer(myShaders.texcoordAttribute, 2, GL_FLOAT,
GL_FALSE, sizeof(Vertex), (GLvoid*)(offsetof(Vertex, uv)));
}
if (myShaders.colorAttribute != -1) {
glEnableVertexAttribArray(myShaders.colorAttribute);
glVertexAttribPointer(myShaders.colorAttribute, 3, GL_FLOAT,
GL_FALSE, sizeof(Vertex), (GLvoid*)(offsetof(Vertex, col)));
}
if (myShaders.MVPuniform != -1) {
glUniformMatrix4fv(myShaders.MVPuniform, 1, GL_FALSE, (GLfloat*) trans.m);
}
// HERE GETS EXCEPTION
glDrawElements(GL_TRIANGLES, num, GL_UNSIGNED_SHORT, (GLvoid*) 0);
eglSwapBuffers (esContext->eglDisplay, esContext->eglSurface);
}
I am not sure that I am correctly binding the buffers in the loadModelNfg() function.
From what can this problem come and how can it be resolved?
EDIT:
GL_VENDOR: Imagination Technologies (Host GL: 'Intel');
GL_RENDERER: PowerVR PVRVFrame 4.2SGX 530 (Host 'Intel(R) HD Graphics 400');
GL_VERSION: OpenGL ES 2.0 (SDK build: 2.04.24.0809)
EDIT:
I surrounded the function with try-catch statement, but it still breaks when calling it:
try {
glDrawElements(GL_TRIANGLES, num, GL_UNSIGNED_SHORT, (GLvoid*)0);
}
catch (const std::exception& e) {
std::cout << e.what() << "\n";
}
I forgot to mention that the project/solution builds successful (after cleaning, or by rebuild).

Answer 1

After learning that OpenGL doesn't throw exceptions, I started looking how it handles errors. I found out that it "returns" error codes (or 0 if success), which can be found with glGetError().
Going withglGetError() through the code, I found out that the error was caused by glUseProgram(myShaders.program);.
Knowing that, I went through the functions which used myShaders variable, and I found that, after calling loadModelNfg("../../ResourcesPacket/Models/Bila.nfg", vbo, ibo, num, myShaders);, the variable got change.
Remembering that I don't use it anymore, I just removed it, and everything was fine.
What is strange is that I didn't modified the myShaders variable anywhere in that function (the code in the question is the final one). The problem, I think, is that I didn't declared the parameter const Shaders shaders.
So, the conclusion:
use glGetError() and breakpoints in code to find the real problem. It may not be the where it breaks!
PS: I hope it's ok that I put this as an answer. If it's not, I'll update the question.