WaveFront .obj loader doesn't display the object like it should (VBO & VAO)

Question

I'm working on a WaveFront .obj Loader and my first goal is to get all the vertices and indices loaded from the following .obj file (displays a cube with curved edges).

# Blender v2.62 (sub 0) OBJ File: 'Cube.blend'
# www.blender.org
o Cube
v 0.900000 -1.000000 -0.900000
v 0.900000 -1.000000 0.900000
v -0.900000 -1.000000 0.900000
v -0.900000 -1.000000 -0.900000
v 0.900000 1.000000 -0.900000
v 0.899999 1.000000 0.900001
v -0.900000 1.000000 0.900000
v -0.900000 1.000000 -0.900000
v 1.000000 -0.900000 -1.000000
v 1.000000 -0.900000 1.000000
v -1.000000 -0.900000 1.000000
v -1.000000 -0.900000 -1.000000
v 1.000000 0.905000 -0.999999
v 0.999999 0.905000 1.000001
v -1.000000 0.905000 1.000000
v -1.000000 0.905000 -1.000000
f 1//1 2//1 3//1
f 1//1 3//1 4//1
f 13//2 9//2 12//2
f 13//2 12//2 16//2
f 5//3 13//3 16//3
f 5//3 16//3 8//3
f 15//4 7//4 8//4
f 15//5 8//5 16//5
f 11//6 15//6 16//6
f 11//6 16//6 12//6
f 14//7 6//7 7//7
f 14//7 7//7 15//7
f 10//8 14//8 11//8
f 14//8 15//8 11//8
f 13//9 5//9 6//9
f 13//9 6//9 14//9
f 9//10 13//10 10//10
f 13//11 14//11 10//11
f 9//12 1//12 4//12
f 9//12 4//12 12//12
f 3//13 11//13 12//13
f 3//14 12//14 4//14
f 2//15 10//15 11//15
f 2//15 11//15 3//15
f 1//16 9//16 10//16
f 1//16 10//16 2//16
f 5//17 8//17 7//17
f 5//17 7//17 6//17

I've loaded all the vertices and the indices in two vectors called verticesVec and indicesVec and I've checked them both (they have all the input in the correct order, verticesVec[0] = 0.9 and indicesVec[0] = 1). I load the vertices in a VertexBufferObject and the indices in a VerticArrayObject together with the shader fields settings.

However, when I'm rendering the cube I get the following image which is not correct. I've rechecked all my code but I can't find the part where I'm going wrong. Has it something to do with the vectors and the size in bytes of the vectors?

The following code is from my Draw/Render method that does all the rendering.

    glUseProgram(theProgram);
    GLuint modelToCameraMatrixUnif = glGetUniformLocation(theProgram, "modelToCameraMatrix");
    GLuint perspectiveMatrixUnif = glGetUniformLocation(theProgram, "cameraToClipMatrix");
    glUniformMatrix4fv(perspectiveMatrixUnif, 1, GL_FALSE, glm::value_ptr(cameraToClipMatrix));

    glm::mat4 identity(1.0f);
    glutil::MatrixStack stack(identity); // Load identity Matrix

    // Push for Camera Stuff
    glutil::PushStack camera(stack);
    stack.Translate(glm::vec3(camX, camY, camZ));

    //Push one step further to fix object 1
    glutil::PushStack push(stack);

    stack.Translate(glm::vec3(0.0f, 0.0f, 3.0f));
    // Draw Blender object
    glBindVertexArray(this->load.vertexArrayOBject);
    glUniformMatrix4fv(modelToCameraMatrixUnif, 1, GL_FALSE, glm::value_ptr(stack.Top()));
    glDrawElements(GL_TRIANGLES, this->load.indicesVec.size(), GL_UNSIGNED_SHORT, 0);

    // Pop camera (call destructor to de-initialize all dynamic memory)
    camera.~PushStack();

    // Now reset all buffers/programs
    glBindVertexArray(0);
    glUseProgram(0);

And the initialisation of buffer objects in my .obj loader:

void Loader::generateVertexBufferObjects()
{
     // Fils the vertex buffer object with data
    glGenBuffers(1, &vertexBufferObject);
    glBindBuffer(GL_ARRAY_BUFFER, vertexBufferObject);
    glBufferData(GL_ARRAY_BUFFER, verticesVec.size() * 4, &verticesVec[0], GL_STATIC_DRAW);
    glBindBuffer(GL_ARRAY_BUFFER, 0);


    // Fills the index buffer object with its data
    glGenBuffers(1, &indexBufferObject);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexBufferObject);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, indicesVec.size() * 4, &indicesVec[0], GL_STATIC_DRAW);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
}

void Loader::generateVertexArrayObjects()
{
    glGenVertexArrays(1, &vertexArrayOBject);
    glBindVertexArray(vertexArrayOBject);

    glBindBuffer(GL_ARRAY_BUFFER, vertexBufferObject);
    glEnableVertexAttribArray(0);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexBufferObject);

    glBindVertexArray(0);
}

Check your indices. The indices in the obj start at 1, but in openGL they start at zero, so you may have to subtract one from all the indices. — Vaughn Cato, Sep 14 '12 at 13:35
@VaughnCato: Good one! Never thought about that. I added a index--; before adding it to the vector but unfortanetly it's still one messy cube so there is something more wrong than just the indices :(. — Joey Dewd, Sep 14 '12 at 13:38
Are your indices really shorts? You've allocated 4 bytes per value, but then told OpenGL they are unsigned short. — Tim, Sep 14 '12 at 15:02
@Tim: Tim, I applaud you. That was indeed the problem, for some reason my mind thought that unsigned shorts were used for ints but they aren't ofcourse. Changed it to GL_UNSIGNED_INT and it worked! If you turn your comment into an answer I'll accept it as the final answer. Thank you :) — Joey Dewd, Sep 14 '12 at 16:07

score 4 · Accepted Answer · answered Sep 14 '12 at 16:09

4

You're creating your indexes as unsigned ints, but you're passing to OpenGL that they are of type GL_UNSIGNED_SHORT. The type argument to glDrawElements must match the type of data uploaded to the index buffer.

answered Sep 14 '12 at 16:09

Tim

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This is the answer; you can actually see the rendering of positive vertices in the example picture. – Krythic May 09 '15 at 19:38

WaveFront .obj loader doesn't display the object like it should (VBO & VAO)

1 Answers1