From d2ae49c97633a4bf4217f6fae82fdfa27f7cf718 Mon Sep 17 00:00:00 2001
From: Eric Wasylishen <ewasylishen@gmail.com>
Date: Sat, 16 Apr 2022 02:09:11 -0600
Subject: [PATCH] qbsp: fix void faces in qbsp_simple_sealed2.map

---
 qbsp/surfaces.cc  | 68 +++++++++++++++++++++++++++++++++++++++++++++--
 qbsp/test_qbsp.cc |  7 +++++
 2 files changed, 73 insertions(+), 2 deletions(-)

diff --git a/qbsp/surfaces.cc b/qbsp/surfaces.cc
index 8067da57..908ee09f 100644
--- a/qbsp/surfaces.cc
+++ b/qbsp/surfaces.cc
@@ -523,6 +523,66 @@ void MakeMarkFaces(mapentity_t* entity, node_t* node)
     MakeMarkFaces(entity, node->children[1]);
 }
 
+static std::list<face_t *> ClipFacesToTree_r(node_t *node, std::list<face_t *> faces)
+{
+    if (node->planenum == PLANENUM_LEAF) {
+        if (node->contents.is_solid(options.target_game)) {
+            // solids eat any faces that reached this point
+            return {};
+        }
+        // other content types let the faces thorugh
+        // fixme-brushbsp: detail?
+        return faces;
+    }
+
+    const qbsp_plane_t &splitplane = map.planes[node->planenum];
+
+    std::list<face_t *> front, back;
+
+    for (auto *face : faces) {
+        auto [frontFragment, backFragment] = SplitFace(face, splitplane);
+        if (frontFragment) {
+            front.push_back(frontFragment);            
+        }
+        if (backFragment) {
+            back.push_back(backFragment);
+        }
+    }
+
+    front = ClipFacesToTree_r(node->children[0], front);
+    back = ClipFacesToTree_r(node->children[1], back);
+
+    // merge lists
+    front.splice(front.end(), back);
+
+    return front;
+}
+
+static std::list<face_t*> ClipFacesToTree(node_t* node, std::list<face_t*> faces)
+{
+    // handles the first level - faces are all supposed to be lying exactly on `node`
+    for (auto *face : faces) {
+        Q_assert(face->planenum == node->planenum);
+    }
+
+    std::list<face_t *> front, back;
+    for (auto *face : faces) {
+        if (face->planeside == 0) {
+            front.push_back(face);
+        } else {
+            back.push_back(face);
+        }
+    }
+
+    front = ClipFacesToTree_r(node->children[0], front);
+    back = ClipFacesToTree_r(node->children[1], back);
+
+    // merge lists
+    front.splice(front.end(), back);
+
+    return front;
+}
+
 static void AddFaceToTree_r(mapentity_t* entity, face_t *face, brush_t *srcbrush, node_t* node)
 {
     if (node->planenum == PLANENUM_LEAF) {
@@ -537,9 +597,13 @@ static void AddFaceToTree_r(mapentity_t* entity, face_t *face, brush_t *srcbrush
         ++c_nodefaces;
 
         // csg it
-        auto csgfaces = CSGFace(face, entity, srcbrush, node);
+        std::list<face_t *> faces = CSGFace(face, entity, srcbrush, node);
 
-        for (face_t *csgface : csgfaces) {
+        // clip them to the descendant parts of the BSP
+        // (otherwise we could have faces floating in the void on this node)
+        faces = ClipFacesToTree(node, faces);
+
+        for (face_t *csgface : faces) {
             // subdivide large faces
             // fixme-brushbsp: weird calling convention
             auto parts = std::list<face_t *>{csgface};
diff --git a/qbsp/test_qbsp.cc b/qbsp/test_qbsp.cc
index e590bbbb..932c7142 100644
--- a/qbsp/test_qbsp.cc
+++ b/qbsp/test_qbsp.cc
@@ -40,6 +40,9 @@ static mbsp_t LoadTestmap(const std::filesystem::path &name)
 {
     map.reset();
 
+    options.nopercent.setValue(true);
+    options.noprogress.setValue(true);
+
     options.szMapName = std::filesystem::path(testmaps_dir) / name;
     options.szBSPName = options.szMapName;
     options.szBSPName.replace_extension(".bsp");
@@ -265,4 +268,8 @@ TEST(qsbsp, simple_sealed2)
     ASSERT_EQ(result.dleafs[0].contents, CONTENTS_SOLID);
     ASSERT_EQ(result.dleafs[1].contents, CONTENTS_EMPTY);
     ASSERT_EQ(result.dleafs[2].contents, CONTENTS_EMPTY);
+
+    // L-shaped room
+    // 2 ceiling + 2 floor + 6 wall faces
+    ASSERT_EQ(result.dfaces.size(), 10);
 }