Selected Vertical Speed change in a C gauge... (Redux)

Note, this was a post from Aug 20 2005 originally. The forum software change following the "hack attack" managed to FUBAR the original code. Also, I've changed from trigger_key_event to send_key_event to eliminate potential conflicts with keyboard input.
Here's one way to get "Vertical Speed Change" working in a C autopilot. VS is selected via the "knob" to descend or ascend. Clicking on the knob's center will "cancel" SVS (Selected Vertical Speed) and return the AP HOLD (current altitude. For brevity, I've only included the relevant parts of the C source code:

/* The two FLOAT64 values may be simple "float" if you wish. 
I have to use FLOAT64 because of the need to convert to WCHAR for a GDI+ string */ 

FLOAT64 vspeed = 0; 

// This variable is used for display of the AUTOPILOT_VERTICAL_HOLD_VAR FLOAT64 dvspeed = 0; 

// This variable is needed because the AUTOPILOT_VERTICAL_HOLD_VAR cannot be "changed" when in ALT HOLD mode 
FLOAT64 oldAlt = 0;

MODULE_VAR AUTOPILOT_ALTITUDE_LOCKvar = {AUTOPILOT_ALTITUDE_LOCK}; 
MODULE_VAR AUTOPILOT_ACTIVEvar = {AUTOPILOT_ACTIVE}; 
MODULE_VAR AUTOPILOT_HEADING_LOCKvar = {AUTOPILOT_HEADING_LOCK}; 
MODULE_VAR AUTOPILOT_NAV1_LOCKvar = {AUTOPILOT_NAV1_LOCK}; 
MODULE_VAR GPS_GROUND_TRACKvar = {GPS_GROUND_TRACK};
MODULE_VAR AUTOPILOT_VERTICAL_HOLD_VARvar = {AUTOPILOT_VERTICAL_HOLD_VAR};
MODULE_VAR AUTOPILOT_VERTICAL_HOLDvar = {AUTOPILOT_VERTICAL_HOLD}; 
MODULE_VAR AUTOPILOT_ATTITUDE_HOLDvar = { AUTOPILOT_ATTITUDE_HOLD }; 
case PANEL_SERVICE_PRE_UPDATE: 
	lookup_var(&AUTOPILOT_ALTITUDE_LOCKvar); 
	lookup_var(&AUTOPILOT_ACTIVEvar); 
	lookup_var(&AUTOPILOT_NAV1_LOCKvar);
	lookup_var(&AUTOPILOT_VERTICAL_HOLD_VARvar); 
	lookup_var(&AUTOPILOT_ATTITUDE_HOLDvar); 
	vspeed = (AUTOPILOT_VERTICAL_HOLD_VARvar.var_value.n);
	lookup_var(&AUTOPILOT_HEADING_LOCKvar); 
	lookup_var(&AUTOPILOT_HEADING_LOCK_DIRvar); 
	hdg = (AUTOPILOT_HEADING_LOCK_DIRvar.var_value.n); 
	lookup_var(&HSI_OBI_NEEDLEvar); 
	crs = (HSI_OBI_NEEDLEvar.var_value.n); 
	lookup_var(&GPS_GROUND_TRACKvar); 
	dtk = RAD_TO_DEG(GPS_GROUND_TRACKvar.var_value.n); 
	break; 

case PANEL_SERVICE_PRE_DRAW: { 
	/* Update Routines */ 
	/* The dvspeed variable is set via the "knob turn" in the mouse callback. */ 
	/* This line ensures that the "selected altitude" is always different (plus or minus) than current altitude! */ 
	if ((ALT_FROM_BAROMETRIC_PRESSUREvar.var_value.n != oldAlt) || (dvspeed != olddvspeed)) 
		{ send_key_event(KEY_AP_ALT_VAR_SET_ENGLISH, (ALT_FROM_BAROMETRIC_PRESSUREvar.var_value.n + dvspeed) ); 
		oldAlt = ALT_FROM_BAROMETRIC_PRESSUREvar.var_value.n; olddvspeed = dvspeed; 
		} 
	}
	break; 
	
	/* This is the DECREASE mousepoint */ 
	BOOL FSAPI DF_mouse_cb2( PPIXPOINT relative_point, FLAGS32 mouse_flags) 
	{ if (mode == 3 || mode == 5) { dvspeed = dvspeed - 100; 
	send_key_event(KEY_AP_VS_VAR_SET_ENGLISH, dvspeed);
	send_key_event(KEY_AP_WING_LEVELER_OFF,0); 
	} 
	return FALSE; } 
	
	/* This is the INCREASE mousepoint */ 
	BOOL FSAPI DF_mouse_cb3( PPIXPOINT relative_point, FLAGS32 mouse_flags) 
	{ if (mode == 3 || mode == 5) { dvspeed = dvspeed + 100; 
	send_key_event(KEY_AP_VS_VAR_SET_ENGLISH, dvspeed); 
	send_key_event(KEY_AP_WING_LEVELER_OFF,0); } return FALSE; 

	} /* This is the CANCEL mousepoint */ 
	BOOL FSAPI DF_mouse_cb4( PPIXPOINT relative_point, FLAGS32 mouse_flags) 
	{ if (mode == 3 || mode == 5 ) { dvspeed = 0; 
	send_key_event(KEY_AP_VS_VAR_SET_ENGLISH, dvspeed); 
	send_key_event(KEY_AP_ALT_VAR_SET_ENGLISH, (ALT_FROM_BAROMETRIC_PRESSUREvar.var_value.n) ); 
	send_key_event(KEY_AP_WING_LEVELER_OFF,0); send_key_event(KEY_AP_PANEL_VS_OFF, 0); 
	}
	}