From e6738f6c20180286e173b20b091bae035113a68d Mon Sep 17 00:00:00 2001
From: Zeno Rogue <zeno@attnam.com>
Date: Mon, 15 May 2023 02:25:13 +0200
Subject: [PATCH] semidirect rendering

---
 drawing.cpp  | 10 +++++++++-
 hypgraph.cpp | 16 ++++++++++++----
 shaders.cpp  |  7 +++++++
 3 files changed, 28 insertions(+), 5 deletions(-)

diff --git a/drawing.cpp b/drawing.cpp
index 036b21bd..b39f98f5 100644
--- a/drawing.cpp
+++ b/drawing.cpp
@@ -509,7 +509,15 @@ void addpoly(const shiftmatrix& V, const vector<glvertex> &tab, int ofs, int cnt
     }
   tofix.clear(); knowgood = false;
   if(in_perspective()) {
-    if(poly_flags & POLY_TRIANGLES) {
+    if(get_shader_flags() & SF_SEMIDIRECT) {
+      dynamicval<bool> d(computing_semidirect, true);
+      for(int i=ofs; i<ofs+cnt; i++) {
+        hyperpoint Hscr;
+        applymodel(V * glhr::gltopoint(tab[i]), Hscr);
+        add1(Hscr);
+        }
+      }
+    else if(poly_flags & POLY_TRIANGLES) {
       for(int i=ofs; i<ofs+cnt; i+=3) {
         shiftpoint h0 = V * glhr::gltopoint(tab[i]);
         shiftpoint h1 = V * glhr::gltopoint(tab[i+1]);
diff --git a/hypgraph.cpp b/hypgraph.cpp
index e13aa282..2e0fc30f 100644
--- a/hypgraph.cpp
+++ b/hypgraph.cpp
@@ -378,7 +378,14 @@ EX ld signed_sqrt(ld x) { return x > 0 ? sqrt(x) : -sqrt(-x); }
 
 EX int axial_x, axial_y;
 
+/** in perspective projections, compute inverse_exp (or similar) on CPU, but perspective on GPU (needs consider_shader_projection off) */
+EX bool semidirect_rendering = false;
+
+/** flag for semidirect_rendering */
+EX bool computing_semidirect = false;
+
 EX void apply_perspective(const hyperpoint& H, hyperpoint& ret) {
+  if(computing_semidirect) { ret = H; ret[3] = 1; return; }
   if(H[2] == 0) { ret[0] = 1e6; ret[1] = 1e6; ret[2] = 0; return; }
   ld ratio = vid.xres / current_display->tanfov / current_display->radius / 2;
   ret[0] = H[0]/H[2] * ratio;
@@ -620,13 +627,14 @@ EX void apply_other_model(shiftpoint H_orig, hyperpoint& ret, eModel md) {
     case mdPerspective: {
       if(gproduct) H = product::inverse_exp(H);
       apply_nil_rotation(H);
-      H = lp_apply(H);
+      if(!computing_semidirect) H = lp_apply(H);
       apply_perspective(H, ret);
       return;      
       }
 
     case mdGeodesic: {
-      auto S = lp_apply(inverse_exp(H_orig, pNORMAL | pfNO_DISTANCE));
+      auto S = inverse_exp(H_orig, pNORMAL | pfNO_DISTANCE);
+      if(!computing_semidirect) S = lp_apply(S);
       apply_perspective(S, ret);
       return;
       }
@@ -645,7 +653,7 @@ EX void apply_other_model(shiftpoint H_orig, hyperpoint& ret, eModel md) {
       #if MAXMDIM >= 4
       S[3] = 1;
       #endif
-      S = lp_apply(S);
+      if(!computing_semidirect) S = lp_apply(S);
       if(hyperbolic) {
         models::apply_orientation(ret[1], ret[0]);
         models::apply_orientation_yz(ret[2], ret[1]);
@@ -657,7 +665,7 @@ EX void apply_other_model(shiftpoint H_orig, hyperpoint& ret, eModel md) {
     #if MAXMDIM >= 4
     case mdRelPerspective: {
       auto S = rel_log(H_orig, true); S[3] = 1;
-      S = lp_apply(S);
+      if(!computing_semidirect) S = lp_apply(S);
       apply_perspective(S, ret);
       return;
       }
diff --git a/shaders.cpp b/shaders.cpp
index 4d7427c8..59316e09 100644
--- a/shaders.cpp
+++ b/shaders.cpp
@@ -32,6 +32,8 @@ constexpr flagtype SF_ORIENT       = 16384;
 constexpr flagtype SF_BOX          = 32768;
 constexpr flagtype SF_ZFOG         = 65536;
 constexpr flagtype SF_ODSBOX       = (1<<17);
+
+constexpr flagtype SF_SEMIDIRECT   = (1<<18);
 #endif
 
 EX bool solv_all;
@@ -236,6 +238,11 @@ shared_ptr<glhr::GLprogram> write_shader(flagtype shader_flags) {
     skip_t = true;
     shader_flags |= SF_DIRECT;
     }
+  else if(!vid.consider_shader_projection && semidirect_rendering && models::is_perspective(pmodel)) {
+    vmain += "// this\n";
+    distfun = "length(t.xyz)";
+    shader_flags |= SF_PERS3 | SF_SEMIDIRECT;
+    }
   else if(!vid.consider_shader_projection) {
     shader_flags |= SF_PIXELS;
     }