From ad65449cefefceb523d947ef9ed2633b879d0b21 Mon Sep 17 00:00:00 2001
From: Eric Wasylishen <ewasylishen@gmail.com>
Date: Mon, 11 Feb 2019 00:52:38 -0700
Subject: [PATCH] qbsp: add "-midsplitsurffraction n" option as an alt. to
 -maxnodesize

switch to midsplit if the node contains more than this fraction of the
model's total surfaces. Try 0.15 to 0.5. Works better than
maxNodeSize for maps with a 3D skybox (e.g. +-128K unit maps)
---
 include/qbsp/qbsp.hh |  8 ++++++++
 qbsp/qbsp.cc         |  8 ++++++++
 qbsp/solidbsp.cc     | 33 +++++++++++++++++++++++++++------
 3 files changed, 43 insertions(+), 6 deletions(-)

diff --git a/include/qbsp/qbsp.hh b/include/qbsp/qbsp.hh
index 4372b3db..7109b18b 100644
--- a/include/qbsp/qbsp.hh
+++ b/include/qbsp/qbsp.hh
@@ -358,6 +358,13 @@ public:
     int dxSubdivide;
     int dxLeakDist;
         int maxNodeSize;
+    /**
+     * if 0 (default), use maxNodeSize for deciding when to switch to midsplit bsp heuristic.
+     *
+     * if 0 < midsplitSurfFraction <=1, switch to midsplit if the node contains more than this fraction of the model's
+     * total surfaces. Try 0.15 to 0.5. Works better than maxNodeSize for maps with a 3D skybox (e.g. +-128K unit maps)
+     */
+    float midsplitSurfFraction;
     char szMapName[512];
     char szBSPName[512];
     char wadPath[512];
@@ -390,6 +397,7 @@ public:
         this->fixRotateObjTexture = true;
         this->fOldaxis = true;
         this->maxNodeSize = 1024;
+        this->midsplitSurfFraction = 0;
         this->on_epsilon = 0.0001;
         this->worldExtent = 65536;
     }
diff --git a/qbsp/qbsp.cc b/qbsp/qbsp.cc
index c825dc79..07c46bf3 100644
--- a/qbsp/qbsp.cc
+++ b/qbsp/qbsp.cc
@@ -854,6 +854,14 @@ ParseOptions(char *szOptions)
                 if (!szTok2)
                     Error("Invalid argument to option %s", szTok);
                 options.maxNodeSize= atoi(szTok2);
+                szTok = szTok2;
+            } else if (!Q_strcasecmp(szTok, "midsplitsurffraction")) {
+                szTok2 = GetTok(szTok + strlen(szTok) + 1, szEnd);
+                if (!szTok2)
+                    Error("Invalid argument to option %s", szTok);
+                options.midsplitSurfFraction = qclamp(atof(szTok2), 0.0f, 1.0f);
+                logprint("Switching to midsplit when node contains more than fraction %f of model's surfaces\n", options.midsplitSurfFraction);
+
                 szTok = szTok2;
             } else if (!Q_strcasecmp(szTok, "epsilon")) {
                 szTok2 = GetTok(szTok + strlen(szTok) + 1, szEnd);
diff --git a/qbsp/solidbsp.cc b/qbsp/solidbsp.cc
index 2f3f3ddc..269a6112 100644
--- a/qbsp/solidbsp.cc
+++ b/qbsp/solidbsp.cc
@@ -31,6 +31,11 @@ static int c_solid, c_empty, c_water, c_detail, c_detail_illusionary, c_detail_f
 static int c_illusionary_visblocker;
 static bool usemidsplit;
 
+/**
+ * Total number of surfaces in the map
+ */
+static int mapsurfaces;
+
 //============================================================================
 
 void
@@ -508,13 +513,24 @@ SelectPartition(surface_t *surfaces)
                 maxs[i] = surf->maxs[i];
         }
 
-    bool largenode = false;
-    if (options.maxNodeSize >= 64) {
-        const vec_t maxnodesize = options.maxNodeSize - ON_EPSILON;
+    // how much of the map are we partitioning?
+    double fractionOfMap = surfcount / (double)mapsurfaces;
 
-        largenode = (maxs[0] - mins[0]) > maxnodesize
-            || (maxs[1] - mins[1]) > maxnodesize
-            || (maxs[2] - mins[2]) > maxnodesize;
+    bool largenode = false;
+
+    // decide if we should switch to the midsplit method
+    if (options.midsplitSurfFraction != 0.0) {
+        // new way (opt-in)
+        largenode = (fractionOfMap > options.midsplitSurfFraction);
+    } else {
+        // old way (ericw-tools 0.15.2+)
+        if (options.maxNodeSize >= 64) {
+            const vec_t maxnodesize = options.maxNodeSize - ON_EPSILON;
+
+            largenode = (maxs[0] - mins[0]) > maxnodesize
+                        || (maxs[1] - mins[1]) > maxnodesize
+                        || (maxs[2] - mins[2]) > maxnodesize;
+        }
     }
 
     if (usemidsplit || largenode) // do fast way for clipping hull
@@ -1044,6 +1060,11 @@ SolidBSP(const mapentity_t *entity, surface_t *surfhead, bool midsplit)
     c_detail_illusionary = 0;
     c_detail_fence = 0;
     c_illusionary_visblocker = 0;
+    // count map surfaces; this is used when deciding to switch between midsplit and the expensive partitioning
+    mapsurfaces = 0;
+    for (surface_t *surf = surfhead; surf; surf = surf->next) {
+        mapsurfaces++;
+    }
 
     PartitionSurfaces(surfhead, headnode);