[Follow] Sit if target is sitting, stand when they stand

Does object and ground sitting.
May fly to sitting target if they're in air
Ground sits as close as it can get if cannot reach ground sitting target

Optimizes following when within desired range of target

Moves sitting/standing autopilot cancels to more proper places

indra/newview/llagent.cpp

@@ -1730,6 +1730,15 @@ void LLAgent::stopAutoPilot(BOOL user_cancel)
 			mAutoPilotFinishedCallback(!user_cancel && dist_vec_squared(gAgent.getPositionGlobal(), mAutoPilotTargetGlobal) < (mAutoPilotStopDistance * mAutoPilotStopDistance), mAutoPilotCallbackData);
 			mAutoPilotFinishedCallback = NULL;
 		}
+
+		// Sit response during follow pilot, now complete, resume follow
+		if (!user_cancel && mAutoPilotBehaviorName == "Sit" && mLeaderID.notNull())
+		{
+			mAutoPilotBehaviorName = "Follow";
+			mAutoPilot = true;
+			return;
+		}
+
 		mLeaderID = LLUUID::null;
 		mAutoPilotNoProgressFrameCount = 0;
 
@@ -1758,14 +1767,54 @@ void LLAgent::autoPilot(F32 *delta_yaw)
 {
 	if (mAutoPilot && isAgentAvatarValid())
 	{
-		bool follow = !mLeaderID.isNull(); //mAutoPilotBehaviorName == "Follow";
+		U8 follow = mLeaderID.notNull(); //mAutoPilotBehaviorName == "Follow";
 		if (follow)
 		{
 			if (auto object = gObjectList.findObject(mLeaderID))
 			{
 				mAutoPilotTargetGlobal = object->getPositionGlobal();
 				if (const auto& av = object->asAvatar()) // Fly if avatar target is flying
+				{
 					setFlying(av->mInAir);
+					if (av->isSitting())
+					{
+						if (!rlv_handler_t::isEnabled() || !gRlvHandler.hasBehaviour(RLV_BHVR_SIT))
+						{
+							if (auto seat = av->getParent())
+							{
+								mAutoPilotNoProgressFrameCount = 0; // Ground Sit may have incremented this, reset it
+								if (gAgentAvatarp->getParent() != seat)
+								{
+									void handle_object_sit(LLViewerObject*, const LLVector3&);
+									handle_object_sit(static_cast<LLViewerObject*>(seat), LLVector3::zero);
+								}
+								return; // If sitting, we won't be moving, exit here
+							}
+							else // Ground sit, but only if near enough
+							{
+								if (dist_vec(av->getPositionAgent(), getPositionAgent()) <= mAutoPilotStopDistance) // We're close enough, sit.
+								{
+									if (!gAgentAvatarp->isSittingAvatarOnGround())
+										setControlFlags(AGENT_CONTROL_SIT_ON_GROUND);
+									mAutoPilotNoProgressFrameCount = 0; // Ground Sit may have incremented this, reset it now
+									return; // We're already sitting on the ground, we have nothing to do
+								}
+								else // We're not close enough yet
+								{
+									if (/*!gAgentAvatarp->isSitting() && */ // RLV takes care of sitting check for us inside standUp
+									  mAutoPilotNoProgressFrameCount <= AUTOPILOT_MAX_TIME_NO_PROGRESS * gFPSClamped) // Only stand up if we haven't exhausted our no progress frames
+										standUp(); // Unsit if need be, so we can move
+									follow = 2; // Indicate we want to groundsit
+								}
+							}
+						}
+					}
+					else if (gAgentAvatarp->isSitting()) // Leader isn't sitting, standUp if needed
+					{
+						standUp();
+						mAutoPilotNoProgressFrameCount = 0; // Ground Sit may have incremented this, reset it
+					}
+				}
 			}
 			else // We might still have a valid avatar pos
 			{
@@ -1777,12 +1826,19 @@ void LLAgent::autoPilot(F32 *delta_yaw)
 					stopAutoPilot();
 					return;
 				}
+				standUp(); // Leader not rendered, we mustn't be sitting
+				mAutoPilotNoProgressFrameCount = 0; // Ground Sit may have incremented this, reset it
 				mAutoPilotTargetGlobal = pos;
 				// Should we fly if the height difference is great enough here? Altitude is often invalid...
 			}
+
+			if (dist_vec(mAutoPilotTargetGlobal, getPositionGlobal()) <= mAutoPilotStopDistance)
+			{
+				follow = 3; // We're close enough, indicate no walking
+			}
 		}
 
-		if (!follow && gAgentAvatarp->mInAir && mAutoPilotAllowFlying)
+		if (follow % 2 == 0 && gAgentAvatarp->mInAir && mAutoPilotAllowFlying)
 		{
 			setFlying(TRUE);
 		}
@@ -1794,12 +1850,15 @@ void LLAgent::autoPilot(F32 *delta_yaw)
 
 		F32 target_dist = direction.magVec();
 
-		if (!follow && target_dist >= mAutoPilotTargetDist)
+		if (follow % 2 == 0 && target_dist >= mAutoPilotTargetDist)
 		{
 			mAutoPilotNoProgressFrameCount++;
 			if (mAutoPilotNoProgressFrameCount > AUTOPILOT_MAX_TIME_NO_PROGRESS * gFPSClamped)
 			{
-				stopAutoPilot();
+				if (follow) // Well, we tried to reach them, let's just ground sit for now.
+					setControlFlags(AGENT_CONTROL_SIT_ON_GROUND);
+				else
+					stopAutoPilot();
 				return;
 			}
 		}
@@ -1841,6 +1900,7 @@ void LLAgent::autoPilot(F32 *delta_yaw)
 		}
 
 		*delta_yaw = yaw;
+		if (follow == 3) return; // We're close enough, all we need to do is turn
 
 		// Compute when to start slowing down
 		F32 slow_distance;

indra/newview/llviewermenu.cpp

@@ -3897,8 +3897,6 @@ void handle_object_sit(LLViewerObject* object, const LLVector3& offset = LLVecto
 		}
 // [/RLVa:KB]
 
-		gAgent.stopAutoPilot(true);
-
 		gMessageSystem->newMessageFast(_PREHASH_AgentRequestSit);
 		gMessageSystem->nextBlockFast(_PREHASH_AgentData);
 		gMessageSystem->addUUIDFast(_PREHASH_AgentID, gAgent.getID());
@@ -3921,9 +3919,10 @@ void handle_object_sit_or_stand()
 		return;
 	}
 
+	gAgent.stopAutoPilot(true);
+
 	if (sitting_on_selection())
 	{
-		gAgent.stopAutoPilot(true);
 		gAgent.standUp();
 		return;
 	}
@@ -9649,6 +9648,7 @@ class ListObjectSit : public view_listener_t
 {
 	bool handleEvent(LLPointer<LLEvent> event, const LLSD& userdata)
 	{
+		gAgent.stopAutoPilot(true);
 		handle_object_sit(gObjectList.findObject(LFIDBearer::getActiveSelectedID()));
 		return true;
 	}