Question

I am attempting to implement a method to draw a bunch of cubes using vertexBufferObjects in OpenGL and Java however am running into a problem when calling the glDrawArrays command.

Essentially what this program does is cycle through x, y, z coordinates and calculates from there where the vertices of a cube centered at that coordinate are and then enters these vertices to a float buffer. (Note I am only entering the vertex data for one face at the moment as to keep the code simple while it is perfected)

The error that occurs is:

EXCEPTION_ACCESS_VIOLATION (0xc0000005) at pc=0x000000006056ec90, pid=6424, tid=7696

int verticesPerObject = 12; //number of vertices per square
int chunkSizeX = 4; //number of cubes in x direction
int chunkSizeY = 4; //number of cubes in y direction
int chunkSizeZ = 4; //number of cubes in z direction
FloatBuffer vertexData = BufferUtils.createFloatBuffer(chunkSizeX * chunkSizeY * chunkSizeZ * verticesPerObject);

    for (int x = 0; x < chunkSizeX; x++) {
        for (int y = 0; y < chunkSizeY; y++) {
            for (int z = 0; z < chunkSizeZ; z++) {
                vertexData.put(new float[]{
                        (float)x * blockWidth - blockWidth/2, (float)y * blockHeight - blockHeight/2, (float)z * blockDepth + blockDepth/2,
                        (float)x * blockWidth + blockWidth/2, (float)y * blockHeight - blockHeight/2, (float)z * blockDepth + blockDepth/2,
                        (float)x * blockWidth + blockWidth/2, (float)y * blockHeight + blockHeight/2, (float)z * blockDepth + blockDepth/2,
                        (float)x * blockWidth - blockWidth/2, (float)y * blockHeight + blockHeight/2, (float)z * blockDepth + blockDepth/2
                });
            }
        }
    }

    vertexData.flip();

    int vboVertexHandle = glGenBuffers();
    glBindBuffer(GL_ARRAY_BUFFER, vboVertexHandle);
    glBufferData(GL_ARRAY_BUFFER, vertexData, GL_STATIC_DRAW);
    glBindBuffer(GL_ARRAY_BUFFER, 0);

    glBindBuffer(GL_ARRAY_BUFFER, vboVertexHandle);
    glVertexPointer(verticesPerObject, GL_FLOAT, 0, 0L);

    glEnableClientState(GL_VERTEX_ARRAY);
    glDrawArrays(GL_QUADS, 0, verticesPerObject);
    glDisableClientState(GL_VERTEX_ARRAY);

Answer 1

Your call to glVertexPointer is wrong. Its first parameter is not the number of overall floats, but the number of floats (or rather components) of a single vertex, in your case 3. The reason for the access violation is just, that the glVertexPointer call fails and glDrawArrays then uses the default parameters, which might specify 4 components per vertex, or not use your buffer object or use some other unspecified parameters not matching your vertex data. So just replace it by

glVertexPointer(3, GL_FLOAT, 0, 0L);

The variable name verticesPerObject is a bit misleading anyway, since it doesn’t contain the number of vertices, but the number of floats, but this is mere cosmetics, the rest of its usage is correct.