Revert of Perform BSP polygon splitting and orientation selection in a single step.

cc/output/bsp_tree.cc

Index: cc/output/bsp_tree.cc
diff --git a/cc/output/bsp_tree.cc b/cc/output/bsp_tree.cc
index 300ba2aebb98a3e5527818c4c776fbb203d36b54..080866f58f9a9bd8c9ed222d802906a48f6eac6c 100644
--- a/cc/output/bsp_tree.cc
+++ b/cc/output/bsp_tree.cc
@@ -44,24 +44,46 @@
   // find a splitting plane, then classify polygons as either in front of
   // or behind that splitting plane.
   while (!polygon_list->empty()) {
-    std::unique_ptr<DrawPolygon> polygon;
-    std::unique_ptr<DrawPolygon> new_front;
-    std::unique_ptr<DrawPolygon> new_back;
-    // Time to split this geometry, *it needs to be split by node_data.
-    polygon = PopFront(polygon_list);
-    bool is_coplanar;
-    node->node_data->SplitPolygon(std::move(polygon), &new_front, &new_back,
-                                  &is_coplanar);
-    if (is_coplanar) {
-      if (new_front)
-        node->coplanars_front.push_back(std::move(new_front));
-      if (new_back)
-        node->coplanars_back.push_back(std::move(new_back));
-    } else {
-      if (new_front)
+    // Is this particular polygon in front of or behind our splitting polygon.
+    BspCompareResult comparer_result =
+        GetNodePositionRelative(*polygon_list->front(), *(node->node_data));
+
+    // If it's clearly behind or in front of the splitting plane, we use the
+    // heuristic to decide whether or not we should put it at the back
+    // or front of the list.
+    switch (comparer_result) {
+      case BSP_FRONT:
+        front_list.push_back(PopFront(polygon_list));
+        break;
+      case BSP_BACK:
+        back_list.push_back(PopFront(polygon_list));
+        break;
+      case BSP_SPLIT:
+      {
+        std::unique_ptr<DrawPolygon> polygon;
+        std::unique_ptr<DrawPolygon> new_front;
+        std::unique_ptr<DrawPolygon> new_back;
+        // Time to split this geometry, *it needs to be split by node_data.
+        polygon = PopFront(polygon_list);
+        bool split_result =
+            polygon->Split(*(node->node_data), &new_front, &new_back);
+        DCHECK(split_result);
+        if (!split_result) {
+          break;
+        }
         front_list.push_back(std::move(new_front));
-      if (new_back)
         back_list.push_back(std::move(new_back));
+        break;
+      }
+      case BSP_COPLANAR_FRONT:
+        node->coplanars_front.push_back(PopFront(polygon_list));
+        break;
+      case BSP_COPLANAR_BACK:
+        node->coplanars_back.push_back(PopFront(polygon_list));
+        break;
+      default:
+        NOTREACHED();
+        break;
     }
   }
 
@@ -78,6 +100,11 @@
   }
 }
 
+BspCompareResult BspTree::GetNodePositionRelative(const DrawPolygon& node_a,
+                                                  const DrawPolygon& node_b) {
+  return DrawPolygon::SideCompare(node_a, node_b);
+}
+
 // The base comparer with 0,0,0 as camera position facing forward
 BspCompareResult BspTree::GetCameraPositionRelative(const DrawPolygon& node) {
   if (node.normal().z() > 0.0f) {