VRPN 06.04

An application can open a dial device, like a knob, which can send differential orientation values back. This class is similar to the vrpn_Analog class, but it deals with dials or other orienters that can turn forever. The same device may be treated as both an analog and a dial by a server program; the client selects which behavior by connecting the appropriate remote class to the server.

Selections from the #include file

//----------------------------------------------------------
// User routine to handle a change in dial values.  This is called when
// the dial callback is called (when a message from its counterpart
// across the connetion arrives).

typedef	struct {
    struct timeval  msg_time;   // Timestamp when change happened
    vrpn_int32      dial;       // which dial changed
    vrpn_float64    change;     // Fraction of a revolution it changed
} vrpn_DIALCB;

typedef void (*vrpn_DIALCHANGEHANDLER) (void * userdata, const vrpn_DIALCB info);

// Open a dial device that is on the other end of a connection
// and handle updates from it.  This is the type of device
// that user code will deal with.

class vrpn_Dial_Remote: public vrpn_Dial {
  public:
    // The name of the device to connect to.
    // Optional argument to be used when the Remote MUST listen on
    // a connection that is already open.
    vrpn_Dial_Remote (const char * name, vrpn_Connection * c = NULL);
    ~vrpn_Dial_Remote();

    // This routine calls the mainloop of the connection it's on
    virtual void mainloop();

    // (un)Register a callback handler to handle dial updates
    virtual int register_change_handler(void *userdata,
        vrpn_DIALCHANGEHANDLER handler);
    virtual int unregister_change_handler(void *userdata,
        vrpn_DIALCHANGEHANDLER handler);
};

Using vrpn_Dial_Remote

A vrpn_Dial_Remote object is used by passing the name of the dial device you want to connect to as a parameter to the constructor, and then using the dial device interface to read in values of different dials. Here is a simple example program that just prints the new value of each dial as the reports arrive:

#include <stdlib.h> 
#include <stdio.h> 
#include <vrpn_Dial.h> 

/***************************************************************************** 
 * 
   Callback handler 
 * 
 *****************************************************************************/ 
 
void	handle_dial (void *, const vrpn_DIALCB d)
{
	printf("Dial %ld spun by %lf\n", d.dial, d.change);
}
 
int main(int argc, char *argv[]) 
{   int done = 0; 
    vrpn_Dial_Remote *dial; 
 
    /* initialize the dial */ 
    dial = new vrpn_Dial_Remote("Dial0@ioglab"); 
 
    // Set up the dial callback handler 
    dial->register_change_handler(NULL, handle_dial); 
 
    /*  
     * main interactive loop 
     */ 
    while ( ! done ) { 
        // Let the dial device do its thing 
        dial->mainloop(); 
    } 
}   /* main */