From ecfdcd67fb6767a7fc2ada8d42ad7d04a1c74ce8 Mon Sep 17 00:00:00 2001
From: pca006132 <john.lck40@gmail.com>
Date: Sun, 5 Jun 2022 22:15:45 +0800
Subject: [PATCH] flatten the tree on the fly if possible

---
 manifold/src/csg_tree.cpp | 16 ++++++++++++----
 manifold/src/csg_tree.h   |  3 ++-
 2 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/manifold/src/csg_tree.cpp b/manifold/src/csg_tree.cpp
index c7c027e3c..652bf19b6 100644
--- a/manifold/src/csg_tree.cpp
+++ b/manifold/src/csg_tree.cpp
@@ -216,12 +216,16 @@ CsgOpNode::CsgOpNode(const std::vector<std::shared_ptr<CsgNode>> &children,
                      Manifold::OpType op)
     : children_(children) {
   SetOp(op);
+  // opportunisticly flatten the tree without costly evaluation
+  GetChildren(false);
 }
 
 CsgOpNode::CsgOpNode(std::vector<std::shared_ptr<CsgNode>> &&children,
                      Manifold::OpType op)
     : children_(children) {
   SetOp(op);
+  // opportunisticly flatten the tree without costly evaluation
+  GetChildren(false);
 }
 
 std::shared_ptr<CsgNode> CsgOpNode::Transform(const glm::mat4x3 &m) const {
@@ -230,6 +234,7 @@ std::shared_ptr<CsgNode> CsgOpNode::Transform(const glm::mat4x3 &m) const {
   node->op_ = op_;
   node->transform_ = m * glm::mat4(transform_);
   node->simplified = simplified;
+  node->flattened = flattened;
   return node;
 }
 
@@ -382,25 +387,28 @@ void CsgOpNode::BatchUnion() const {
 
 /**
  * Flatten the children to a list of leaf nodes and return them.
+ * If finalize is true, the list will be guaranteed to be a list of leaf nodes
+ * (i.e. no ops). Otherwise, the list may contain ops.
  * Note that this function will not apply the transform to children, as they may
  * be shared with other nodes.
  */
-std::vector<std::shared_ptr<CsgNode>> &CsgOpNode::GetChildren() const {
-  if (children_.empty() || simplified) return children_;
+std::vector<std::shared_ptr<CsgNode>> &CsgOpNode::GetChildren(bool finalize) const {
+  if (children_.empty() || (simplified && !finalize) || flattened) return children_;
   simplified = true;
+  flattened = finalize;
   std::vector<std::shared_ptr<CsgNode>> newChildren;
 
   CsgNodeType op = op_;
   for (auto &child : children_) {
     if (child->GetNodeType() == op) {
       auto grandchildren =
-          std::dynamic_pointer_cast<CsgOpNode>(child)->GetChildren();
+          std::dynamic_pointer_cast<CsgOpNode>(child)->GetChildren(finalize);
       int start = children_.size();
       for (auto &grandchild : grandchildren) {
         newChildren.push_back(grandchild->Transform(child->GetTransform()));
       }
     } else {
-      if (child->GetNodeType() == CsgNodeType::LEAF) {
+      if (!finalize || child->GetNodeType() == CsgNodeType::LEAF) {
         newChildren.push_back(child);
       } else {
         newChildren.push_back(child->ToLeafNode());
diff --git a/manifold/src/csg_tree.h b/manifold/src/csg_tree.h
index c1ac601bd..5962eef8c 100644
--- a/manifold/src/csg_tree.h
+++ b/manifold/src/csg_tree.h
@@ -72,6 +72,7 @@ class CsgOpNode final : public CsgNode {
   mutable std::vector<std::shared_ptr<CsgNode>> children_;
   mutable std::shared_ptr<CsgLeafNode> cache_ = nullptr;
   mutable bool simplified = false;
+  mutable bool flattened = false;
 
   void SetOp(Manifold::OpType);
 
@@ -81,7 +82,7 @@ class CsgOpNode final : public CsgNode {
 
   void BatchUnion() const;
 
-  std::vector<std::shared_ptr<CsgNode>> &GetChildren() const;
+  std::vector<std::shared_ptr<CsgNode>> &GetChildren(bool finalize = true) const;
 };
 
 }  // namespace manifold