Passing a pointer to an array to glGenBuffers

Question

I'm currently passing an array to a function, then attempting to use glGenBuffers with the array that is passed to the function. I can't figure out a way to get glGenBuffers to work with the array that I've passed. I have a decent grasp of the basics of pointers, but this is beyond me.

Buffers are generated (and deleted) elsewhere. I can render everything if I do it fixed, but this makes it more flexible. The current issue is "&renderArray[0]". If I move this (everything into the function) out so that it is in the main drawing code, it works. I also have something very similar that uses a constant array working as well.

This is basically how the render code works. It's a bit more complex, (colours using the same array idea, also not working) but the basic idea is as follows:

void drawFoo(const GLfloat *renderArray, GLuint verticeBuffer) {
    glBindBuffer(GL_ARRAY_BUFFER, verticeBuffer);
    glBufferData(GL_ARRAY_BUFFER, sizeof(renderArray)*sizeof(GLfloat), &renderArray[0], GL_STATIC_DRAW);
    glVertexPointer(2, GL_FLOAT, 0, 0);

    glEnableClientState(GL_VERTEX_BUFFER);
    glDrawArrays(GL_TRIANGLE_FAN, 0, 45);
    glDisableClientState(GL_VERTEX_BUFFEr);
}

Thanks in advance for the help

Answer 1

If you pass an array as a pointer, you lose its associated type information:

GLfloat array[N];
GLfloat* pointer = array;
sizeof(array  ); // => sizeof(GLfloat) * N
sizeof(pointer); // => sizeof(GLfloat*);

sizeof is a compile time operator which gives you the size of the type of its operand, which in your case is GLfloat*.

You need to pass the size of the array as an additional parameter:

void drawFoo(const GLfloat* renderArray, size_t nFloats, GLuint verticeBuffer) {
    // ...
    glBufferData(GL_ARRAY_BUFFER, nFloats * sizeof(GLFloat), 
                 renderArray, GL_STATIC_DRAW);

Also note that the &array[0] syntax is redundant, renderArray already is a pointer. Even with arrays such an expression is not needed as arrays can implicitly decay to a pointer to their first element.