Questions on OpenGL VBOs

Question

I'm currently trying to make a basic game with cubey terrain, similar to Minecraft classic. My first question:

How do I store a list of cubes in a VBO and then rebuild the list when I change that data? I currently render cubes like this:

vertices = BufferUtils.createFloatBuffer(3 * 4 * 6);
    vertices.put(new float[] {
            -1.0f, -1.0f, 1.0f,
            1.0f, -1.0f, 1.0f,
            1.0f, 1.0f, 1.0f,
            -1.0f, 1.0f, 1.0f,

            -1.0f, -1.0f, -1.0f,
            -1.0f, 1.0f, -1.0f,
            1.0f, 1.0f, -1.0f,
            1.0f, -1.0f, -1.0f,

            -1.0f, 1.0f, -1.0f,
            -1.0f, 1.0f, 1.0f,
            1.0f, 1.0f, 1.0f,
            1.0f, 1.0f, -1.0f,

            -1.0f, -1.0f, -1.0f,
            1.0f, -1.0f, -1.0f,
            1.0f, -1.0f, 1.0f,
            -1.0f, -1.0f, 1.0f,

            1.0f, -1.0f, -1.0f,
            1.0f, 1.0f, -1.0f,
            1.0f, 1.0f, 1.0f,
            1.0f, -1.0f, 1.0f,

            -1.0f, -1.0f, -1.0f,
            -1.0f, -1.0f, 1.0f,
            -1.0f, 1.0f, 1.0f,
            -1.0f, 1.0f, -1.0f});
    vertices.rewind();

    vertexBufferID = createVBOID();
    bufferData(vertexBufferID, vertices);

         public static int createVBOID() {
        if (GLContext.getCapabilities().GL_ARB_vertex_buffer_object) {
            IntBuffer buffer = BufferUtils.createIntBuffer(1);
            ARBVertexBufferObject.glGenBuffersARB(buffer);
            return buffer.get(0);
        }
        return 0;
    }

 public static void bufferData(int id, FloatBuffer buffer) {
        ARBVertexBufferObject.glBindBufferARB(ARBVertexBufferObject.GL_ARRAY_BUFFER_ARB, id);
        ARBVertexBufferObject.glBufferDataARB(ARBVertexBufferObject.GL_ARRAY_BUFFER_ARB, buffer, ARBVertexBufferObject.GL_DYNAMIC_DRAW_ARB);
    } 

public void renderGL() {
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glClearColor(0.0f, 0.0f, 0.0f, 0.5f);
    glViewport(0, 0, Display.getWidth(), Display.getHeight());
    glLoadIdentity();

    glRotatef(xrot, 1.0f, 0.0f, 0.0f);
    glRotatef(yrot, 0.f, 1.0f, 0.0f);
    glTranslated(-xpos, -ypos - 19, -zpos - 5);

    glEnableClientState(GL_VERTEX_ARRAY);
    ARBVertexBufferObject.glBindBufferARB(ARBVertexBufferObject.GL_ARRAY_BUFFER_ARB, vertexBufferID);
    glVertexPointer(3, GL_FLOAT, 0, 0);

    for (int y = 0; y < 16; y++) {
        for (int x = 0; x < 16; x++) {
            for (int z = 0; z < 16; z++) {
                glPushMatrix();
                glTranslatef(x, y, z);
                glDrawArrays(GL_QUADS, 0, 24);
                glPopMatrix();
            }
        }

    }
    glDisableClientState(GL_VERTEX_ARRAY);
}

I know I need to use glMapBuffer and glUnMapBuffer to modify the VBO, but how do I store the cubes and remove them when needed? Should I use an ArrayList? Also, I've been told my way of rendering the cubes is wrong because everyone says I'm rendering one cube only with new coordinates. They say my vertex data stays the same, what do they mean by that?

So basically my questions are, 1. How do I use a Array to hold a list of cubes and load them into a VBO and then remove some of the cubes? 2. How can I change my vertex data so I'm rendering different cubes, not just one cube over and over?

I would just make one vbo and translate it to different places. — antonijn

Spektre Spektre · Accepted Answer · 2013-09-13T15:19:37

as antonijn wrote you can have 1 cube as VBO and translating its modelview matrix
- the translation is sometimes slower (when there are too much cubes).
- the translation can be done even inside shader by some uniform offset which is little bit faster than matrix translations
faster way is to have all of the cubes in VBO
- it wastes memory but cubes are not that much big (6 faces only)
I would have the cubes stored permanently in CPU accessible memory
- when scene changes copy it to VBO for rendering.
- do not transfering data between CPU<->GPU back and forward
- only copy data from CPU to GPU.
also is better to use non indexed VBOs (drawarrays not drawelements)
- indexing is not very good supported
- often slows thing down even crashes on bad drivers

for the code look here: https://stackoverflow.com/a/18672821/2521214 but that post use VAO+VBO for GLSL purposes so if you not using GLSL then some changes are needed.

Questions on OpenGL VBOs

2 Answers