XEEN: Fix object 0 not being removable, _objNumber cleanup

The original used 0 as "unset", and object index + 1 to indicate the
object at the current location. Given all the +1/-1 usages, I've
simplified the use of _objNumber to use -1 as unset, allowing the
direct object index to be used otherwise

4 files changed, 17 insertions, 18 deletions

diff --git a/engines/xeen/interface_scene.cpp b/engines/xeen/interface_scene.cpp
index 043ef2cbbe..2fcb378537 100644
--- a/engines/xeen/interface_scene.cpp
+++ b/engines/xeen/interface_scene.cpp
@@ -380,7 +380,7 @@ InterfaceScene::InterfaceScene(XeenEngine *vm): _vm(vm) {
 	_flipDefaultGround = false;
 	_isAttacking = false;
 	_charsShooting = false;
-	_objNumber = 0;
+	_objNumber = -1;
 	_combatFloatCounter = 0;
 	_thinWall = false;
 	_isAnimReset = false;
@@ -392,9 +392,8 @@ void InterfaceScene::drawScene() {
 	Map &map = *_vm->_map;
 	Scripts &scripts = *_vm->_scripts;
 
-	MazeObject &objObject = map._mobData._objects[_objNumber];
+	MazeObject *obj = (_objNumber == -1) ? nullptr : &map._mobData._objects[_objNumber];
 	Direction partyDirection = _vm->_party->_mazeDirection;
-	int objNum = _objNumber - 1;
 
 	// Loop to update the frame numbers for each maze object, applying the animation frame
 	// limits as specified by the map's _animationInfo listing
@@ -407,9 +406,9 @@ void InterfaceScene::drawScene() {
 			mazeObject._frame = animEntry._frame1._frames[directionIndex];
 		} else {
 			++mazeObject._frame;
-			if ((int)idx == objNum && scripts._animCounter > 0 && (
-				objObject._spriteId == (_vm->_files->_ccNum ? 15 : 16) ||
-				objObject._spriteId == 58 || objObject._spriteId == 73)) {
+			if ((int)idx == _objNumber && scripts._animCounter > 0 && (
+				obj->_spriteId == (_vm->_files->_ccNum ? 15 : 16) ||
+				obj->_spriteId == 58 || obj->_spriteId == 73)) {
 				if (mazeObject._frame > 4 || mazeObject._spriteId == 58)
 					mazeObject._frame = 1;
 			} else if (mazeObject._frame >= animEntry._frame2._frames[directionIndex]) {
@@ -599,7 +598,7 @@ void InterfaceScene::drawIndoorsScene() {
 	_isAnimReset = false;
 
 	// Code in the original that's not being used
-	//MazeObject &objObject = map._mobData._objects[_objNumber - 1];
+	//MazeObject &objObject = map._mobData._objects[_objNumber];
 
 	// Only the front rank of pow points result in a Pow splatter effect
 	for (int idx = 0; idx < 3; ++idx) {
@@ -2652,7 +2651,7 @@ void InterfaceScene::setIndoorsObjects() {
 	Common::Point mazePos = _vm->_party->_mazePosition;
 	Direction dir = _vm->_party->_mazeDirection;
 	Common::Point pt;
-	_objNumber = 0;
+	_objNumber = -1;
 
 	Common::Array<MazeObject> &objects = _vm->_map->_mobData._objects;
 	for (uint idx = 0; idx < objects.size(); ++idx) {
@@ -3361,6 +3360,7 @@ void InterfaceScene::setOutdoorsObjects() {
 	const Common::Point &pt = party._mazePosition;
 	Direction dir = party._mazeDirection;
 	int posIndex;
+	_objNumber = -1;
 
 	for (uint idx = 0; idx < map._mobData._objects.size(); ++idx) {
 		MazeObject &obj = map._mobData._objects[idx];
diff --git a/engines/xeen/map.cpp b/engines/xeen/map.cpp
index 19312b6bcc..b0c269cdab 100644
--- a/engines/xeen/map.cpp
+++ b/engines/xeen/map.cpp
@@ -636,7 +636,7 @@ void Map::load(int mapId) {
 	PleaseWait waitMsg(intf._falling);
 	waitMsg.show();
 
-	intf._objNumber = 0;
+	intf._objNumber = -1;
 	party._stepped = true;
 	party._mazeId = mapId;
 	saveMaze();
diff --git a/engines/xeen/party.cpp b/engines/xeen/party.cpp
index 31a43be0a4..d92a4952cc 100644
--- a/engines/xeen/party.cpp
+++ b/engines/xeen/party.cpp
@@ -1439,8 +1439,8 @@ bool Party::giveExt(int mode1, uint val1, int mode2, uint val2, int mode3, uint
 	Sound &sound = *g_vm->_sound;
 	Character &c = _itemsCharacter;
 
-	if (intf._objNumber && !scripts._animCounter) {
-		MazeObject &obj = map._mobData._objects[intf._objNumber - 1];
+	if (intf._objNumber != -1 && !scripts._animCounter) {
+		MazeObject &obj = map._mobData._objects[intf._objNumber];
 		switch (obj._spriteId) {
 		case 15:
 			if (!files._ccNum)
diff --git a/engines/xeen/scripts.cpp b/engines/xeen/scripts.cpp
index 3a3c9d6d65..896387f4d3 100644
--- a/engines/xeen/scripts.cpp
+++ b/engines/xeen/scripts.cpp
@@ -210,8 +210,8 @@ int Scripts::checkEvents() {
 	if (party._treasure._hasItems || party._treasure._gold || party._treasure._gems)
 		party.giveTreasure();
 
-	if (_animCounter > 0 && intf._objNumber) {
-		MazeObject &selectedObj = map._mobData._objects[intf._objNumber - 1];
+	if (_animCounter > 0 && intf._objNumber != -1) {
+		MazeObject &selectedObj = map._mobData._objects[intf._objNumber];
 
 		if (selectedObj._spriteId == (ccNum ? 15 : 16)) {
 			for (uint idx = 0; idx < 16; ++idx) {
@@ -240,8 +240,8 @@ int Scripts::checkEvents() {
 
 	if (_scriptExecuted)
 		intf.clearEvents();
-	if (_scriptExecuted || !intf._objNumber || _dirFlag) {
-		if (_dirFlag && !_scriptExecuted && intf._objNumber && !map._currentIsEvent) {
+	if (_scriptExecuted || intf._objNumber == -1 || _dirFlag) {
+		if (_dirFlag && !_scriptExecuted && intf._objNumber != -1 && !map._currentIsEvent) {
 			sound.playFX(21);
 		}
 	} else {
@@ -496,8 +496,7 @@ bool Scripts::cmdTeleport(ParamsIterator &params) {
 
 	party._stepped = true;
 	if (mapId != party._mazeId) {
-		int spriteId = (intf._objNumber == 0) ? -1 :
-			map._mobData._objects[intf._objNumber - 1]._spriteId;
+		int spriteId = (intf._objNumber == -1) ? -1 : map._mobData._objects[intf._objNumber - 1]._spriteId;
 
 		switch (spriteId) {
 		case 47:
@@ -798,7 +797,7 @@ bool Scripts::cmdRemove(ParamsIterator &params) {
 	Interface &intf = *_vm->_interface;
 	Map &map = *_vm->_map;
 
-	if (intf._objNumber) {
+	if (intf._objNumber != -1) {
 		// Give the active object a completely way out of bounds position
 		MazeObject &obj = map._mobData._objects[intf._objNumber];
 		obj._position = Common::Point(128, 128);