add the ability to specify a chop order; this is to help with "nested" func_groups and layers, since TB makes them an implicit object at random spots in the BSP. Now you can be sure your objects will chop in the right order.

include/qbsp/map.hh

@@ -108,6 +108,7 @@ public:
     mapentity_t *func_areaportal = nullptr;
     bool is_hint = false; // whether we are a hint brush or not (at least one side is "hint" or SURF_HINT)
     bool no_chop = false; // don't chop this
+    int32_t chop_index = 0; // chopping order; higher numbers chop lower numbers
 };
 
 struct lumpdata

qbsp/map.cc

@@ -3161,10 +3161,19 @@ void ProcessMapBrushes()
                 brush.func_areaportal = areaportal;
                 brush.is_hint = MapBrush_IsHint(brush);
 
+                // _chop signals that a brush does not partake in the BSP chopping phase.
+                // this allows brushes embedded in others to be retained.
                 if (entity.epairs.has("_chop") && !entity.epairs.get_int("_chop")) {
                     brush.no_chop = true;
                 }
 
+                // brushes are sorted by their _chop_order; higher numbered brushes
+                // will "eat" lower numbered brushes. This effectively overrides the
+                // brush order of the map.
+                if (entity.epairs.has("_chop_order")) {
+                    brush.chop_index = entity.epairs.get_int("_chop_order");
+                }
+
                 // calculate brush bounds
                 CalculateBrushBounds(brush);
 

qbsp/qbsp.cc

@@ -1036,6 +1036,14 @@ static void ProcessEntity(mapentity_t &entity, hull_index_t hullnum)
 
     // always chop the other hulls to reduce brush tests
     if (qbsp_options.chop.value() || hullnum.value_or(0)) {
+        std::sort(brushes.begin(), brushes.end(), [](const bspbrush_t::ptr &a, const bspbrush_t::ptr &b) -> bool {
+            if (a->mapbrush->chop_index == b->mapbrush->chop_index) {
+                return a->mapbrush->line.line_number < b->mapbrush->line.line_number;
+            }
+
+            return a->mapbrush->chop_index < b->mapbrush->chop_index;
+        });
+
         ChopBrushes(brushes, qbsp_options.chopfragment.value());
     }