vertexAttribPointer method
Implementation
void vertexAttribPointer(
    int index, int size, int type, bool normalized, int stride, int offset) {
  var offsetPointer = Pointer<Void>.fromAddress(offset);
  gl.glVertexAttribPointer(index, size, type, normalized ? 1 : 0, stride,
      offsetPointer.cast<Void>());
}