Problem with Vertex Buffer/Index Buffer Combination [Qt 4.8, C++]

[Christian Lohr]

Hello,
I have the problem, that when I use Vertex Buffer Array in combination with Index Buffer Arrays, nothing appears on the screen. If I'm using only a Vertex Buffer Array, that works fine. I uploaded the project: example_VertexAttrib.zip (works with Qt 4.8 and above)

My Header includes both arrays:

    QVector<float> vertices_;
    QVector<short> indices_;

I'm initializing both arrays in the Constructor:

    /* Push back all vertices */
    vertices_.reserve(16);
    vertices_
            << -1 << -1 << -1     // a 0
            << 1 << -1 << -1      // b 1
            << 1 << 1 << -1      // c 2
            << -1 << 1 << -1       // d 3
 
            << -1 << -1 << 1       // e 4
            << 1 << -1 << 1       // f 5
            << 1 << 1 << 1       // g 6
            << -1 << 1 << 1;    // h 7
 
    /* Push back all indices */
    indices_.reserve(16);
    indices_
            << 0 << 1 << 2 << 3      // front
            << 4 << 5 << 6 << 7      // rear
            << 1 << 5 << 6 << 2      // right
            << 4 << 0 << 3 << 7;    // left

Buffer Objects are prepared inside QGLWidget::initializeGL()

static const int VERTICES = 0;
static const int INDICES = 1;
 
    // -- Buffer Objects --
    GLuint bufferObjectVertices;
    GLuint bufferObjectIndices;
 
    QGLFunctions::glGenBuffers(1, &bufferObjectVertices);
    QGLFunctions::glGenBuffers(1, &bufferObjectIndices);
 
    QGLFunctions::glBindBuffer(GL_ARRAY_BUFFER, bufferObjectVertices);
    QGLFunctions::glBufferData(GL_ARRAY_BUFFER, vertices_.size() * sizeof(float), &vertices_.front(), GL_STATIC_DRAW);
 
    QGLFunctions::glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, bufferObjectIndices);
    QGLFunctions::glBufferData(GL_ELEMENT_ARRAY_BUFFER, indices_.size() * sizeof(short), &indices_.front(), GL_STATIC_DRAW);
 
    QGLFunctions::glVertexAttribPointer(VERTICES, 3, GL_FLOAT, false, 0, 0);
    QGLFunctions::glEnableVertexAttribArray(VERTICES);
 
    GLuint programId = shaderProg_.programId();
 
    QGLFunctions::glBindAttribLocation(programId, VERTICES, "Vertex");

And I'm trying to draw them inside QGLWidget:aintGL()

glDrawElements(GL_QUADS, indices_.size(), GL_SHORT, 0);

[V-man]

Did you check if all is OK? Did you use glGetError()?

http://www.opengl.org/wiki/Common_Mistakes#glGetError

[Christian Lohr]

Good idea. I fixed it (it was an invalid enum). Instead of

glDrawElements(GL_QUADS, indices_.size(), GL_SHORT, 0);

I wrote

glDrawElements(GL_QUADS, indices_.size(), GL_UNSIGNED_SHORT, 0);