Problems using VBOs to render vertices - OpenGL

Question

I am transferring over my vertex arrays functions to VBOs to increase the speed of my application.

Here was my original working vertex array rendering function:

void BSP::render()
{
    glFrontFace(GL_CCW);

    // Set up rendering states
    glEnableClientState(GL_VERTEX_ARRAY);
    glEnableClientState(GL_TEXTURE_COORD_ARRAY);

    glVertexPointer(3, GL_FLOAT, sizeof(Vertex), &vertices[0].x);

    glTexCoordPointer(2, GL_FLOAT, sizeof(Vertex), &vertices[0].u);

    // Draw
    glDrawElements(GL_TRIANGLES, numIndices, GL_UNSIGNED_SHORT, indices);

    // End of rendering - disable states
    glDisableClientState(GL_VERTEX_ARRAY);
    glDisableClientState(GL_TEXTURE_COORD_ARRAY);
}

Worked great!

Now I am moving them into VBOs and my program actually caused my graphics card to stop responding. The setup on my vertices and indices are exactly the same.

New setup:

vboId is setup in the bsp.h like so: GLuint vboId[2];

I get no error when I just run the createVBO() function!

void BSP::createVBO()
{

    // Generate buffers
    glGenBuffers(2, vboId);

    // Bind the first buffer (vertices)
    glBindBuffer(GL_ARRAY_BUFFER, vboId[0]);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

    // Now save indices data in buffer
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, vboId[1]);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);

}

And the rendering code for the VBOS. I am pretty sure it's in here. Just want to render whats in the VBO like I did in the vertex array.

Render:

void BSP::renderVBO()
{
    glBindBuffer(GL_ARRAY_BUFFER, vboId[0]);         // for vertex coordinates
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, vboId[1]); // for indices

    // do same as vertex array except pointer
    glEnableClientState(GL_VERTEX_ARRAY);             // activate vertex coords array
    glVertexPointer(3, GL_FLOAT, 0, 0);               // last param is offset, not ptr

    // draw the bsp area
    glDrawElements(GL_TRIANGLES, numVertices, GL_UNSIGNED_BYTE, BUFFER_OFFSET(0));

    glDisableClientState(GL_VERTEX_ARRAY);            // deactivate vertex array

    // bind with 0, so, switch back to normal pointer operation
    glBindBuffer(GL_ARRAY_BUFFER, 0);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
}

Not sure what the error is but I am pretty sure I have my rendering function wrong. Wish there was a more unified tutorial on this as there are a bunch online but they are often contradicting eachother.

Answer 1

In addition what Miro said (the GL_UNSIGNED_BYTE should be GL_UNSIGNED_SHORT), I don't think you want to use numVertices but numIndices, like in your non-VBO call.

glDrawElements(GL_TRIANGLES, numIndices, GL_UNSIGNED_SHORT, 0);

Otherwise your code looks quite valid and if this doesn't fix your problem, maybe the error is somewhere else.

And by the way the BUFFER_OFFSET(i) thing is usuaully just a define for ((char*)0+(i)), so you can also just pass in the byte offset directly, especially when it's 0.

EDIT: Just spotted another one. If you use the exact data structures you use for the non-VBO version (which I assumed above), then you of course need to use sizeof(Vertex) as stride parameter in glVertexPointer.