From e8e6d0aa252e5957f1228aec61172e4f171d2b61 Mon Sep 17 00:00:00 2001
From: Zeno Rogue <zeno@attnam.com>
Date: Thu, 16 Sep 2021 22:26:23 +0200
Subject: [PATCH] two-sided display of hyperbolic disk with -1<pconf.alpha<0

---
 drawing.cpp | 5 ++++-
 shaders.cpp | 2 +-
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/drawing.cpp b/drawing.cpp
index 08e6b60a..0b9ae85f 100644
--- a/drawing.cpp
+++ b/drawing.cpp
@@ -306,7 +306,7 @@ EX bool two_sided_model() {
   if(in_vr_sphere) return true;
   if(pmodel == mdHyperboloid) return !euclid && !in_vr;
   // if(pmodel == mdHemisphere) return true;
-  if(pmodel == mdDisk) return sphere;
+  if(pmodel == mdDisk) return sphere || (hyperbolic && pconf.alpha < 0 && pconf.alpha > -1);
   if(pmodel == mdRetroLittrow) return sphere;
   if(pmodel == mdRetroHammer) return sphere;
   if(pmodel == mdHemisphere) return !in_vr;
@@ -333,6 +333,9 @@ EX int get_side(const hyperpoint& H) {
     double horizon = curnorm / pconf.alpha;
     return (H[2] <= -horizon) ? -1 : 1;
     }
+  if(pmodel == mdDisk && hyperbolic && pconf.alpha < 0 && pconf.alpha > -1) {
+    return (H[2] * (H[2] + pconf.alpha) < sqhypot_d(2, H)) ? -1 : 1;
+    }
   if(pmodel == mdRetroLittrow && sphere) {
     return H[2] >= 0 ? 1 : -1;
     }
diff --git a/shaders.cpp b/shaders.cpp
index 18dbe621..9540e43e 100644
--- a/shaders.cpp
+++ b/shaders.cpp
@@ -171,7 +171,7 @@ shared_ptr<glhr::GLprogram> write_shader(flagtype shader_flags) {
   else if(!vid.consider_shader_projection) {
     shader_flags |= SF_PIXELS;
     }        
-  else if(among(pmodel, mdDisk, mdBall) && GDIM == 2 && vrhr::rendering() && !sphere) {
+  else if(among(pmodel, mdDisk, mdBall) && GDIM == 2 && vrhr::rendering() && !sphere && !(hyperbolic && pconf.alpha < 0 && pconf.alpha > -1)) {
     shader_flags |= SF_DIRECT | SF_BOX;
     vsh += "uniform mediump float uAlpha, uDepth, uDepthScaling, uCamera;";