Allocates shared memory to use for passing data to the display processes, and returns a pointer to one block for the computation process to use. size is the size of the block in bytes. Four blocks of memory are actually allocated - the one that is returned, one for the display processes to use, and two others that are used in staging the data when it is sent by CAVEPassDisplayData(). The blocks are all allocated using CAVEMalloc(), so its shared arena must be large enough to hold the four blocks, plus any other shared data the application will allocate (the size can be set by CAVESetOption()).
When this function is used instead of CAVEAllocDisplayDataByID(), the application must make sure that all the calls occur in one process, in the same order on all machines.