basic opengl black screen when adding IBO

Question

When i only have a VBO and a VAO all works fine but when adding an IBO i'm getting a black screen. Here is the code:

initialisation:

GLuint vbo = 0;
glGenBuffers(1, &vbo);
glBindBuffer(GL_ARRAY_BUFFER, vbo);
glBufferData(GL_ARRAY_BUFFER, sizeof(points), points, GL_STATIC_DRAW);

GLuint  ibo;
glGenBuffers(1, &ibo);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ibo);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);

GLuint vao = 0;
glGenVertexArrays(1, &vao);
glBindVertexArray(vao);
glBindBuffer(GL_ARRAY_BUFFER, vbo);

glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, sizeof(float), NULL);

glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ibo);
glBindVertexArray(0);

inside loop:

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glUseProgram(shader_programme);
glBindVertexArray(vao);
glDrawElements(GL_TRIANGLES, 14, GL_UNSIGNED_INT, NULL);
glBindVertexArray(0);

vertices and indicies:

float   points[] = {
    -1.0, -1.0,  1.0,
    1.0, -1.0,  1.0,
    -1.0,  1.0,  1.0,
    1.0,  1.0,  1.0,
    -1.0, -1.0, -1.0,
    1.0, -1.0, -1.0,
    -1.0,  1.0, -1.0,
    1.0,  1.0, -1.0,
};

float   indices[] = {
    0, 1, 2, 3, 7, 1, 5, 4, 7, 6, 2, 4, 0, 1
};

Answer 1

The 5th parameter of glVertexAttribPointer is the byte offset between consecutive generic vertex attributes. If it is 0 then the vertex attributes are understood to be tightly packed.

Your vertices consists of three components of type float, so the stride is 3*sizeof(float):

glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3*sizeof(float), NULL);

Since the vertices are tightly packed, you can also pass 0 to the paramter:

glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, NULL);     

---

The type of the indices is GL_UNSIGNED_INT. The type of the index array has to be an integral data type which corresponds to GL_UNSIGNED_INT. In your case it has to be unsigned int.

unsigned int indices[] = { .... }; 

Further, the primitive type GL_TRIANGLES consists of a list of indices where each 3 form a triangle. Indices 0, 1, 2 for ma triangle, indices 4, 5, 6 form the next triangle and so on. So the number of indices has to be dividable by 3.

If you want to draw a cube, then the list of indices may look like this:

unsigned int indices[] = {
    0,1,2,    0,2,3,
    1,5,6,    1,6,2,
    5,4,7,    5,7,6,
    4,0,3,    4,3,7,
    3,2,6,    3,6,7,
    1,0,4,    1,4,5 
};

glDrawElements(GL_TRIANGLES, 36, GL_UNSIGNED_INT, NULL);