Footsteps: Fix offset footstep and shallow water sound bugs

Fix footstep sounds coming from nodes to either side when walking on a
1 node wide row of nodebox slabs such as default:snow.
Fix sand footsteps when swimming in 1 node deep water.

Use a new function 'getFootstepNodePos()' instead of 'getStandingNodePos()'
to avoid using a horizontally-offset 'sneak node' for sounds.

Sound is selected from the node BS * 0.05 below the player's feet, so
that 1/16th slabs will play the slab sound but 1/32nd slabs will not.
If the player is not 'touching ground' the node detection position is
changed to BS * 0.5 below to preserve footstep sounds when landing after
a jump or fall.

src/game.cpp

@@ -3530,7 +3530,7 @@ void Game::updateSound(f32 dtime)
 	LocalPlayer *player = client->getEnv().getLocalPlayer();
 
 	ClientMap &map = client->getEnv().getClientMap();
-	MapNode n = map.getNodeNoEx(player->getStandingNodePos());
+	MapNode n = map.getNodeNoEx(player->getFootstepNodePos());
 	soundmaker->m_player_step_sound = nodedef_manager->get(n).sound_footstep;
 }
 

src/localplayer.cpp

@@ -655,6 +655,18 @@ v3s16 LocalPlayer::getStandingNodePos()
 	return floatToInt(getPosition() - v3f(0, BS, 0), BS);
 }
 
+v3s16 LocalPlayer::getFootstepNodePos()
+{
+	if (touching_ground)
+		// BS * 0.05 below the player's feet ensures a 1/16th height
+		// nodebox is detected instead of the node below it.
+		return floatToInt(getPosition() - v3f(0, BS * 0.05f, 0), BS);
+	// A larger distance below is necessary for a footstep sound
+	// when landing after a jump or fall. BS * 0.5 ensures water
+	// sounds when swimming in 1 node deep water.
+	return floatToInt(getPosition() - v3f(0, BS * 0.5f, 0), BS);
+}
+
 v3s16 LocalPlayer::getLightPosition() const
 {
 	return floatToInt(m_position + v3f(0,BS+BS/2,0), BS);

src/localplayer.h

@@ -68,6 +68,7 @@ public:
 	void applyControl(float dtime);
 
 	v3s16 getStandingNodePos();
+	v3s16 getFootstepNodePos();
 
 	// Used to check if anything changed and prevent sending packets if not
 	v3f last_position;