Fix shape index in multiple physics queries with Bullet

Two main changes:

- Better handling of concave shapes to make sure the queries don't
return a triangle index instead of shape index.
Note: A concave shape within a compound shape will always return a shape
index of 0 because of Bullet limitations.

- Extra check for compound shapes in some queries to avoid undefined
behavior, because the shape index can have an uninitialized value with
convex shapes in some cases.

(cherry picked from commit 02d40de30d727bb23ae7ed9dc003a36e6d5f4764)

modules/bullet/godot_result_callbacks.cpp

@@ -113,7 +113,14 @@ btScalar GodotAllConvexResultCallback::addSingleResult(btCollisionWorld::LocalCo
 
 	PhysicsDirectSpaceState::ShapeResult &result = m_results[count];
 
-	result.shape = convexResult.m_localShapeInfo->m_triangleIndex; // "m_triangleIndex" Is a odd name but contains the compound shape ID
+	// Triangle index is an odd name but contains the compound shape ID.
+	// A shape part of -1 indicates the index is a shape index and not a triangle index.
+	if (convexResult.m_localShapeInfo && convexResult.m_localShapeInfo->m_shapePart == -1) {
+		result.shape = convexResult.m_localShapeInfo->m_triangleIndex;
+	} else {
+		result.shape = 0;
+	}
+
 	result.rid = gObj->get_self();
 	result.collider_id = gObj->get_instance_id();
 	result.collider = 0 == result.collider_id ? nullptr : ObjectDB::get_instance(result.collider_id);
@@ -179,11 +186,14 @@ bool GodotClosestConvexResultCallback::needsCollision(btBroadphaseProxy *proxy0)
 }
 
 btScalar GodotClosestConvexResultCallback::addSingleResult(btCollisionWorld::LocalConvexResult &convexResult, bool normalInWorldSpace) {
-	if (convexResult.m_localShapeInfo) {
-		m_shapeId = convexResult.m_localShapeInfo->m_triangleIndex; // "m_triangleIndex" Is a odd name but contains the compound shape ID
+	// Triangle index is an odd name but contains the compound shape ID.
+	// A shape part of -1 indicates the index is a shape index and not a triangle index.
+	if (convexResult.m_localShapeInfo && convexResult.m_localShapeInfo->m_shapePart == -1) {
+		m_shapeId = convexResult.m_localShapeInfo->m_triangleIndex;
 	} else {
 		m_shapeId = 0;
 	}
+
 	return btCollisionWorld::ClosestConvexResultCallback::addSingleResult(convexResult, normalInWorldSpace);
 }
 
@@ -228,10 +238,22 @@ btScalar GodotAllContactResultCallback::addSingleResult(btManifoldPoint &cp, con
 		CollisionObjectBullet *colObj;
 		if (m_self_object == colObj0Wrap->getCollisionObject()) {
 			colObj = static_cast<CollisionObjectBullet *>(colObj1Wrap->getCollisionObject()->getUserPointer());
-			result.shape = cp.m_index1;
+			// Checking for compound shape because the index might be uninitialized otherwise.
+			// A partId of -1 indicates the index is a shape index and not a triangle index.
+			if (colObj1Wrap->getCollisionObject()->getCollisionShape()->isCompound() && cp.m_partId1 == -1) {
+				result.shape = cp.m_index1;
+			} else {
+				result.shape = 0;
+			}
 		} else {
 			colObj = static_cast<CollisionObjectBullet *>(colObj0Wrap->getCollisionObject()->getUserPointer());
-			result.shape = cp.m_index0;
+			// Checking for compound shape because the index might be uninitialized otherwise.
+			// A partId of -1 indicates the index is a shape index and not a triangle index.
+			if (colObj0Wrap->getCollisionObject()->getCollisionShape()->isCompound() && cp.m_partId0 == -1) {
+				result.shape = cp.m_index0;
+			} else {
+				result.shape = 0;
+			}
 		}
 
 		result.collider_id = colObj->get_instance_id();
@@ -322,14 +344,26 @@ btScalar GodotRestInfoContactResultCallback::addSingleResult(btManifoldPoint &cp
 		CollisionObjectBullet *colObj;
 		if (m_self_object == colObj0Wrap->getCollisionObject()) {
 			colObj = static_cast<CollisionObjectBullet *>(colObj1Wrap->getCollisionObject()->getUserPointer());
-			m_result->shape = cp.m_index1;
+			// Checking for compound shape because the index might be uninitialized otherwise.
+			// A partId of -1 indicates the index is a shape index and not a triangle index.
+			if (colObj1Wrap->getCollisionObject()->getCollisionShape()->isCompound() && cp.m_partId1 == -1) {
+				m_result->shape = cp.m_index1;
+			} else {
+				m_result->shape = 0;
+			}
 			B_TO_G(cp.getPositionWorldOnB(), m_result->point);
 			B_TO_G(cp.m_normalWorldOnB, m_result->normal);
 			m_rest_info_bt_point = cp.getPositionWorldOnB();
 			m_rest_info_collision_object = colObj1Wrap->getCollisionObject();
 		} else {
 			colObj = static_cast<CollisionObjectBullet *>(colObj0Wrap->getCollisionObject()->getUserPointer());
-			m_result->shape = cp.m_index0;
+			// Checking for compound shape because the index might be uninitialized otherwise.
+			// A partId of -1 indicates the index is a shape index and not a triangle index.
+			if (colObj0Wrap->getCollisionObject()->getCollisionShape()->isCompound() && cp.m_partId0 == -1) {
+				m_result->shape = cp.m_index0;
+			} else {
+				m_result->shape = 0;
+			}
 			B_TO_G(cp.m_normalWorldOnB * -1, m_result->normal);
 			m_rest_info_bt_point = cp.getPositionWorldOnA();
 			m_rest_info_collision_object = colObj0Wrap->getCollisionObject();

modules/bullet/godot_result_callbacks.h

@@ -74,8 +74,10 @@ public:
 	virtual bool needsCollision(btBroadphaseProxy *proxy0) const;
 
 	virtual btScalar addSingleResult(btCollisionWorld::LocalRayResult &rayResult, bool normalInWorldSpace) {
-		if (rayResult.m_localShapeInfo) {
-			m_shapeId = rayResult.m_localShapeInfo->m_triangleIndex; // "m_triangleIndex" Is a odd name but contains the compound shape ID
+		// Triangle index is an odd name but contains the compound shape ID.
+		// A shape part of -1 indicates the index is a shape index and not a triangle index.
+		if (rayResult.m_localShapeInfo && rayResult.m_localShapeInfo->m_shapePart == -1) {
+			m_shapeId = rayResult.m_localShapeInfo->m_triangleIndex;
 		} else {
 			m_shapeId = 0;
 		}