qbsp: import BaseWindingForNode from qbsp3

include/qbsp/qbsp.hh

@@ -355,6 +355,7 @@ struct portal_t;
 struct node_t
 {
     aabb3d bounds; // bounding volume, not just points inside
+    node_t *parent;
 
     // information for decision nodes
     int planenum; // -1 = leaf node

qbsp/portals.cc

@@ -225,6 +225,39 @@ static void CheckLeafPortalConsistancy(node_t *node)
 
 //============================================================================
 
+/*
+================
+BaseWindingForNode
+
+Creates a winding from the given node plane, clipped by all parent nodes.
+================
+*/
+#define	BASE_WINDING_EPSILON	0.001
+#define	SPLIT_WINDING_EPSILON	0.001
+
+std::optional<winding_t> BaseWindingForNode(node_t *node)
+{
+    auto plane = map.planes.at(node->planenum);
+
+    std::optional<winding_t> w = BaseWindingForPlane(plane);
+
+    // clip by all the parents
+    for (node_t *np = node->parent; np && w; )
+    {
+        plane = map.planes.at(np->planenum);
+
+        const side_t keep = (np->children[0] == node) ?
+            SIDE_FRONT : SIDE_BACK;
+
+        w = w->clip(plane, BASE_WINDING_EPSILON, false)[keep];
+
+        node = np;
+        np = np->parent;
+    }
+
+    return w;
+}
+
 /*
 ================
 CutNodePortals_r

qbsp/solidbsp.cc

@@ -865,7 +865,9 @@ static void PartitionBrushes(std::vector<std::unique_ptr<brush_t>> brushes, node
     splitnodes++;
 
     node->children[0] = new node_t{};
+    node->children[0]->parent = node;
     node->children[1] = new node_t{};
+    node->children[1]->parent = node;
     node->planenum = FindPositivePlane(split->planenum);
 
     node->detail_separator = AllDetail(brushes);
@@ -933,9 +935,11 @@ tree_t *BrushBSP(mapentity_t *entity, bool midsplit)
         headnode->children[0] = new node_t{};
         headnode->children[0]->planenum = PLANENUM_LEAF;
         headnode->children[0]->contents = options.target_game->create_empty_contents();
+        headnode->children[0]->parent = headnode;
         headnode->children[1] = new node_t{};
         headnode->children[1]->planenum = PLANENUM_LEAF;
         headnode->children[1]->contents = options.target_game->create_empty_contents();
+        headnode->children[1]->parent = headnode;
 
         tree->headnode = headnode;
         tree->bounds = headnode->bounds;