From e7aeba9d8fd947dfc6e6b23e1e38c93cb0a89e93 Mon Sep 17 00:00:00 2001
From: p2r3 <p2r3@p2r3.com>
Date: Thu, 21 Aug 2025 03:09:01 +0300
Subject: [PATCH] simplify biome grid building

---
 include/tools.h |  7 ++++++-
 src/globals.c   |  2 +-
 src/worldgen.c  | 17 +++++++----------
 3 files changed, 14 insertions(+), 12 deletions(-)

diff --git a/include/tools.h b/include/tools.h
index 0032844..59d72c2 100644
--- a/include/tools.h
+++ b/include/tools.h
@@ -6,7 +6,12 @@
 
 #include "globals.h"
 
-#define mod_abs(a, b) ((a % b + b) % b)
+inline int mod_abs (int a, int b) {
+  return ((a % b) + b) % b;
+}
+inline int div_floor (int a, int b) {
+  return a < 0 ? (a - b) / b : a / b;
+}
 
 ssize_t recv_all (int client_fd, void *buf, size_t n, uint8_t require_first);
 ssize_t send_all (int fd, const void *buf, size_t len);
diff --git a/src/globals.c b/src/globals.c
index fdaa2c2..0046632 100644
--- a/src/globals.c
+++ b/src/globals.c
@@ -26,7 +26,7 @@
 ssize_t recv_count;
 uint8_t recv_buffer[256] = {0};
 
-uint32_t world_seed = 0xA103DE6B;
+uint32_t world_seed = 0xA103DE6C;
 uint32_t rng_seed = 0xE2B9419;
 
 uint16_t client_count;
diff --git a/src/worldgen.c b/src/worldgen.c
index 3a66901..156f5b9 100644
--- a/src/worldgen.c
+++ b/src/worldgen.c
@@ -26,14 +26,6 @@ uint8_t getChunkBiome (short x, short z) {
   x += BIOME_RADIUS;
   z += BIOME_RADIUS;
 
-  // Calculate "biome coordinates" (one step above chunk coordinates)
-  // The pattern repeats every 4 biomes, so the coordinate range is [0;3]
-  uint8_t _x = mod_abs(x / BIOME_SIZE, 16) & 3;
-  uint8_t _z = mod_abs(z / BIOME_SIZE, 16) & 3;
-  // To prevent obvious mirroring, invert values on negative axes
-  if (x < 0) _x = 3 - _x;
-  if (z < 0) _z = 3 - _z;
-
   // Calculate distance from biome center
   int8_t dx = BIOME_RADIUS - mod_abs(x, BIOME_SIZE);
   int8_t dz = BIOME_RADIUS - mod_abs(z, BIOME_SIZE);
@@ -41,12 +33,17 @@ uint8_t getChunkBiome (short x, short z) {
   // Determine whether the given chunk is within the island
   if (dx * dx + dz * dz > BIOME_RADIUS * BIOME_RADIUS) return W_beach;
 
-  // Finally, the biome itself is plucked from the world seed.
+  // Calculate "biome coordinates" (one step above chunk coordinates)
+  short biome_x = div_floor(x, BIOME_SIZE);
+  short biome_z = div_floor(z, BIOME_SIZE);
+
+  // The biome itself is plucked directly from the world seed.
   // The 32-bit seed is treated as a 4x4 biome matrix, with each biome
   // taking up 2 bytes. This is why there are only 4 biomes, excluding
   // beaches. Using the world seed as a repeating pattern avoids
   // having to generate and layer yet another hash.
-  return (world_seed >> (_x + _z * 4)) & 3;
+  uint8_t index = abs((biome_x & 3) + ((biome_z * 4) & 15));
+  return (world_seed >> (index * 2)) & 3;
 
 }