OSX programmatically invoke sound level graphic - macos

Question

I have an app which can change the volume under OSX. What it lacks is the visual feedback provided when one presses the sound up/down keys. Does anyone know how to programmatically invoke that behavior?
Thanks

Answer 1

Here's a little code from George Warner and Casey Fleser that does this trick. Think carefully that this is really the way you want to do things.
// Save as sound_up.m
// Compile: gcc -o sound_up sound_up.m -framework IOKit -framework Cocoa
#import <Cocoa/Cocoa.h>
#import <IOKit/hidsystem/IOHIDLib.h>
#import <IOKit/hidsystem/ev_keymap.h>
static io_connect_t get_event_driver(void)
{
static mach_port_t sEventDrvrRef = 0;
mach_port_t masterPort, service, iter;
kern_return_t kr;
if (!sEventDrvrRef)
{
// Get master device port
kr = IOMasterPort( bootstrap_port, &masterPort );
check( KERN_SUCCESS == kr);
kr = IOServiceGetMatchingServices( masterPort, IOServiceMatching( kIOHIDSystemClass ), &iter );
check( KERN_SUCCESS == kr);
service = IOIteratorNext( iter );
check( service );
kr = IOServiceOpen( service, mach_task_self(),
kIOHIDParamConnectType, &sEventDrvrRef );
check( KERN_SUCCESS == kr );
IOObjectRelease( service );
IOObjectRelease( iter );
}
return sEventDrvrRef;
}
static void HIDPostAuxKey( const UInt8 auxKeyCode )
{
NXEventData event;
kern_return_t kr;
IOGPoint loc = { 0, 0 };
// Key press event
UInt32 evtInfo = auxKeyCode << 16 | NX_KEYDOWN << 8;
bzero(&event, sizeof(NXEventData));
event.compound.subType = NX_SUBTYPE_AUX_CONTROL_BUTTONS;
event.compound.misc.L[0] = evtInfo;
kr = IOHIDPostEvent( get_event_driver(), NX_SYSDEFINED, loc, &event, kNXEventDataVersion, 0, FALSE );
check( KERN_SUCCESS == kr );
// Key release event
evtInfo = auxKeyCode << 16 | NX_KEYUP << 8;
bzero(&event, sizeof(NXEventData));
event.compound.subType = NX_SUBTYPE_AUX_CONTROL_BUTTONS;
event.compound.misc.L[0] = evtInfo;
kr = IOHIDPostEvent( get_event_driver(), NX_SYSDEFINED, loc, &event, kNXEventDataVersion, 0, FALSE );
check( KERN_SUCCESS == kr );
}
int main(int argc, char *argv[]) {
HIDPostAuxKey(NX_KEYTYPE_SOUND_UP);
}
Other interesting keycodes include: NX_KEYTYPE_SOUND_DOWN, NX_KEYTYPE_MUTE, NX_KEYTYPE_PLAY.

Answer 2

I would implement this by simulating the physical press of the up/down volume keys, and letting the OS deal with the details. Perhaps the user has disabled the visual feedback, perhaps it changes, etc. - this is the safest way of pulling it off.
Have a look at this: Simulating key press events in Mac OS X