From 5a40534c851350c8370978916af37c6017d5e1be Mon Sep 17 00:00:00 2001
From: Zeno Rogue <zeno@attnam.com>
Date: Sat, 18 Feb 2023 19:33:27 +0100
Subject: [PATCH] embeddings:: star probability configurable

---
 config.cpp |  3 +++
 sky.cpp    | 15 +++++++++++++--
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/config.cpp b/config.cpp
index 1849f523..0811ccb5 100644
--- a/config.cpp
+++ b/config.cpp
@@ -2397,6 +2397,7 @@ EX void show3D_height_details() {
     add_edit(vid.infdeep_height);
     add_edit(vid.sun_size);
     add_edit(vid.star_size);
+    add_edit(star_prob);
     add_edit(vid.height_limits);
     if(euclid && msphere) add_edit(use_euclidean_infinity);
     }
@@ -2763,6 +2764,8 @@ EX int config3 = addHook(hooks_configfile, 100, [] {
     ->editable(0, 10, .1, "sun size (relative to item sizes)", "", '8');
   param_f(vid.star_size, "star_size", "star_size", 0.75)
     ->editable(0, 10, .1, "night star size (relative to item sizes)", "", '9');
+  param_f(star_prob, "star_prob", 0.3)
+    ->editable(0, 1, .01, "star probability", "probability of star per tile", '*');
   param_b(vid.height_limits, "height_limits", true)
     ->editable("automatically limit heights if too high", 'l');
   param_b(auto_remove_roofs, "auto_remove_roofs", true)
diff --git a/sky.cpp b/sky.cpp
index 59f113c3..03d6893d 100644
--- a/sky.cpp
+++ b/sky.cpp
@@ -357,6 +357,17 @@ void draw_star(const shiftmatrix& V, const hpcshape& sh, color_t col, ld rev = f
   queuepolyat(V1 * zpush(val), sh, col, PPR::SKY);
   }
 
+EX ld star_prob = 0.33;
+
+/* the first star is supposed to appear as long as probability > 0 */
+EX vector<ld> stars = {1e-20};
+
+EX bool star_for(int i) {
+  i = i & ((1<<16)-1);
+  while(isize(stars) <= i) stars.push_back(randd());
+  return stars[i] < star_prob;
+  }
+
 void celldrawer::draw_ceiling() {
 
   if(!models::is_perspective(pmodel) || sphere) return;
@@ -368,11 +379,11 @@ void celldrawer::draw_ceiling() {
   switch(ceiling_category(c)) {
     /* ceilingless levels */
     case 1: {
-      if(fieldpattern::fieldval_uniq(c) % 3 == 0)
+      if(star_for(fieldpattern::fieldval_uniq(c)))
         draw_star(V, cgi.shNightStar, 0xFFFFFFFF);
       add_to_sky(0x00000F, 0x00000F);
       if(c->land == laAsteroids) {
-        if(fieldpattern::fieldval_uniq(c) % 9 < 3)
+        if(star_for(fieldpattern::fieldval_uniq(c) ^ 0x5555))
           draw_star(V, cgi.shNightStar, 0xFFFFFFFF, true);
         int sk = get_skybrightness(-1);
         auto sky = draw_shapevec(c, V * MirrorZ, cgi.shFullFloor.levels[SIDE_SKY], 0x000000FF + 0x100 * (sk/17), PPR::SKY);