From 42f96b768cbf2b82db82f0af7982fdce4ea5ca1d Mon Sep 17 00:00:00 2001
From: Zeno Rogue <zeno@attnam.com>
Date: Sun, 4 Dec 2022 14:48:12 +0100
Subject: [PATCH] improvements to sphere flipping

---
 basegraph.cpp | 2 +-
 drawing.cpp   | 6 +++---
 graph.cpp     | 3 ++-
 hypgraph.cpp  | 8 +++++---
 vr.cpp        | 2 +-
 5 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/basegraph.cpp b/basegraph.cpp
index 0b4ba2ae..de13a17a 100644
--- a/basegraph.cpp
+++ b/basegraph.cpp
@@ -927,7 +927,7 @@ EX int rhypot(int a, int b) { return (int) sqrt(a*a - b*b); }
 EX ld realradius() {
   ld vradius = current_display->radius;
   if(sphere) {
-    if(sphereflipped()) 
+    if(flip_sphere())
       vradius /= sqrt(pconf.alpha*pconf.alpha - 1);
     else
       vradius = 1e12; // use the following
diff --git a/drawing.cpp b/drawing.cpp
index 84081eb5..6bd48f90 100644
--- a/drawing.cpp
+++ b/drawing.cpp
@@ -2184,7 +2184,7 @@ EX void quickqueue() {
 
 /* todo */
 ld xintval(const shiftpoint& h) {
-  if(sphereflipped()) return -h.h[2];
+  if(sphere_flipped) return -h.h[2];
   if(hyperbolic) return -h.h[2];
   return -intval(h.h, C0);
   }
@@ -2198,7 +2198,7 @@ int qp[PMAX], qp0[PMAX];
 
 color_t darken_color(color_t& color, bool outline) {
   int alpha = color & 255;
-  if(sphere && pmodel == mdDisk && pconf.alpha <= 1)
+  if(sphere && pmodel == mdDisk && pconf.alpha <= 0.99)
     return 0;
   else {
     if(outline && alpha < 255) 
@@ -2279,7 +2279,7 @@ EX void draw_backside() {
         ptd->draw();
     }
 
-  spherespecial = sphereflipped() ? 1 : -1;
+  spherespecial = sphere_flipped ? 1 : -1;
   reset_projection();
   
   if(pmodel == mdRotatedHyperboles) {
diff --git a/graph.cpp b/graph.cpp
index 9db5f0c8..343aab1e 100644
--- a/graph.cpp
+++ b/graph.cpp
@@ -5030,7 +5030,8 @@ EX bool nonisotropic_weird_transforms;
 
 EX void make_actual_view() {
   sphereflip = Id;
-  if(sphereflipped()) sphereflip[LDIM][LDIM] = -1;
+  sphere_flipped = flip_sphere();
+  if(sphere_flipped) sphereflip[LDIM][LDIM] = -1;
   actual_view_transform = sphereflip;  
   if(vid.yshift && WDIM == 2) actual_view_transform = ypush(vid.yshift) * actual_view_transform;
   #if MAXMDIM >= 4
diff --git a/hypgraph.cpp b/hypgraph.cpp
index b961c405..ba6b93cb 100644
--- a/hypgraph.cpp
+++ b/hypgraph.cpp
@@ -11,9 +11,11 @@ namespace hr {
 hyperpoint ghxy, ghgxy;
 shiftpoint ghpm = shiftless(C02);
 
-#if HDR
-inline bool sphereflipped() { return sphere && pconf.alpha > 1.1; }
-#endif
+EX ld flip_limit = 1.1;
+
+EX bool flip_sphere() { return sphere && pconf.alpha > flip_limit; }
+
+EX bool sphere_flipped;
 
 void ghcheck(hyperpoint &ret, const shiftpoint &H) {
   if(hypot_d(2, ret-ghxy) < hypot_d(2, ghgxy-ghxy)) {
diff --git a/vr.cpp b/vr.cpp
index 0ae46b8e..455003e7 100644
--- a/vr.cpp
+++ b/vr.cpp
@@ -577,7 +577,7 @@ EX hyperpoint model_location(shiftpoint h, bool& bad) {
     h.h = hmd_pre_for[2] * h.h;
     eModel md = pmodel_3d_version();
     apply_other_model(h, hscr, md);
-    bad = in_vr_sphere && get_side(hscr) == (sphereflipped() ? -1 : 1);
+    bad = in_vr_sphere && get_side(hscr) == (sphere_flipped ? -1 : 1);
   
     hscr[3] = 1;
     return hscr;