From 04141aa59d5dc6bdc31d1eb397ddd7d6d6806336 Mon Sep 17 00:00:00 2001
From: Jonathan Westhues <jwesthues@cq.cx>
Date: Thu, 7 Feb 2008 01:57:59 -0800
Subject: [PATCH] Go back to randomizing the faces before adding to the BSP,
 rather than sorting by area. I had hoped that would help with normal
 accuracy, but I don't think it helped much, and it sometimes became very
 slow.

[git-p4: depot-paths = "//depot/solvespace/": change = 1850]
---
 bsp.cpp | 27 +++++++--------------------
 1 file changed, 7 insertions(+), 20 deletions(-)

diff --git a/bsp.cpp b/bsp.cpp
index adfeab4d..177ea296 100644
--- a/bsp.cpp
+++ b/bsp.cpp
@@ -3,22 +3,6 @@
 SBsp2 *SBsp2::Alloc(void) { return (SBsp2 *)AllocTemporary(sizeof(SBsp2)); }
 SBsp3 *SBsp3::Alloc(void) { return (SBsp3 *)AllocTemporary(sizeof(SBsp3)); }
 
-static int ByArea(const void *av, const void *bv) {
-    STriangle *a = (STriangle *)av;
-    STriangle *b = (STriangle *)bv;
-
-    double fa = a->Normal().Magnitude();
-    double fb = b->Normal().Magnitude();
-
-    if(fa > fb) {
-        return -1;
-    } else if(fa < fb) {
-        return 1;
-    } else {
-        return 0;
-    }
-}
-
 SBsp3 *SBsp3::FromMesh(SMesh *m) {
     SBsp3 *bsp3 = NULL;
     int i;
@@ -28,10 +12,13 @@ SBsp3 *SBsp3::FromMesh(SMesh *m) {
         mc.AddTriangle(&(m->l.elem[i]));
     }
 
-    // The larger-area triangles have more trustworthy normals. By inserting
-    // those first, we hope to improve the numerical accuracy of our
-    // split planes.
-    qsort(mc.l.elem, mc.l.n, sizeof(mc.l.elem[0]), ByArea);
+    srand(0); // Let's be deterministic, at least!
+    int n = mc.l.n;
+    while(n > 1) {
+        int k = rand() % n;
+        n--;
+        SWAP(STriangle, mc.l.elem[k], mc.l.elem[n]);
+    }
 
     for(i = 0; i < mc.l.n; i++) {
         bsp3 = bsp3->Insert(&(mc.l.elem[i]), NULL);