SCI32: Add feature detection for plane id base

This provides a generic fix for AddScreenItem crashes in early SCI32
floppy games that have previously required individual script patches.

3 files changed, 13 insertions, 3 deletions

diff --git a/engines/sci/engine/features.cpp b/engines/sci/engine/features.cpp
index 06fa046228..df57655d8a 100644
--- a/engines/sci/engine/features.cpp
+++ b/engines/sci/engine/features.cpp
@@ -628,6 +628,14 @@ MessageTypeSyncStrategy GameFeatures::getMessageTypeSyncStrategy() const {
 	return kMessageTypeSyncStrategyNone;
 }
 
+int GameFeatures::detectPlaneIdBase() {
+	if (getSciVersion() == SCI_VERSION_2 &&
+	    g_sci->getGameId() != GID_PQ4)
+		return 0;
+	else
+		return 20000;
+}
+	
 bool GameFeatures::autoDetectMoveCountType() {
 	// Look up the script address
 	reg_t addr = getDetectionAddr("Motion", SELECTOR(doit));
diff --git a/engines/sci/engine/features.h b/engines/sci/engine/features.h
index 7a1c6f59aa..d776495c2f 100644
--- a/engines/sci/engine/features.h
+++ b/engines/sci/engine/features.h
@@ -228,6 +228,8 @@ public:
 	 */
 	MoveCountType detectMoveCountType();
 
+	int detectPlaneIdBase();
+	
 	bool handleMoveCount() { return detectMoveCountType() == kIncrementMoveCount; }
 
 	bool usesCdTrack() { return _usesCdTrack; }
diff --git a/engines/sci/graphics/plane32.cpp b/engines/sci/graphics/plane32.cpp
index 46a8aedbb0..c85965e755 100644
--- a/engines/sci/graphics/plane32.cpp
+++ b/engines/sci/graphics/plane32.cpp
@@ -44,8 +44,8 @@ void DrawList::add(ScreenItem *screenItem, const Common::Rect &rect) {
 
 #pragma mark -
 #pragma mark Plane
-uint16 Plane::_nextObjectId = 20000;
-uint32 Plane::_nextCreationId = 0;
+uint16 Plane::_nextObjectId; // Will be initialized in Plane::init()
+uint32 Plane::_nextCreationId; // ditto
 
 Plane::Plane(const Common::Rect &gameRect, PlanePictureCodes pictureId) :
 _creationId(_nextCreationId++),
@@ -132,7 +132,7 @@ void Plane::operator=(const Plane &other) {
 }
 
 void Plane::init() {
-	_nextObjectId = 20000;
+	_nextObjectId = g_sci->_features->detectPlaneIdBase();
 	_nextCreationId = 0;
 }