commit 8193df09e09d6e711ec2ceb7b7de49414f44a51f
Author: shylie <shylie@shylie.info>
Date:   Sat Apr 18 11:00:58 2026 -0400

    Initial commit

diff --git a/.clang-format b/.clang-format
new file mode 100644
index 0000000..f1b5bbc
--- /dev/null
+++ b/.clang-format
@@ -0,0 +1,12 @@
+BasedOnStyle: GNU
+SpaceBeforeParens: ControlStatementsExceptControlMacros
+PointerAlignment: Left
+UseTab: Never
+IndentWidth: 2
+ContinuationIndentWidth: 2
+ConstructorInitializerIndentWidth: 2
+BreakAfterReturnType: Automatic
+BreakConstructorInitializers: AfterColon
+PackConstructorInitializers: Never
+IncludeBlocks: Regroup
+BreakBeforeBraces: Allman
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..567609b
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+build/
diff --git a/CMakeLists.txt b/CMakeLists.txt
new file mode 100644
index 0000000..3652580
--- /dev/null
+++ b/CMakeLists.txt
@@ -0,0 +1,32 @@
+cmake_minimum_required(VERSION 3.20)
+
+project(sand)
+
+find_package(PkgConfig REQUIRED)
+pkg_check_modules(LUAJIT REQUIRED luajit)
+
+add_library(sand SHARED
+  src/sand.cpp
+  src/lualib.cpp
+)
+
+target_include_directories(sand
+  PUBLIC include
+  PRIVATE ${LUAJIT_INCLUDE_DIRS}
+)
+target_link_libraries(sand PRIVATE ${LUAJIT_LIBRARIES})
+set_target_properties(sand PROPERTIES
+  CXX_STANDARD 20
+  CXX_STANDARD_REQUIRED ON
+)
+
+find_package(SDL3 CONFIG REQUIRED)
+
+add_executable(sandtest
+  src/main.cpp
+)
+target_link_libraries(sandtest PRIVATE sand SDL3)
+set_target_properties(sandtest PROPERTIES
+  CXX_STANDARD 20
+  CXX_STANDARD_REQUIRED ON
+)
diff --git a/include/sand.h b/include/sand.h
new file mode 100644
index 0000000..890b9e6
--- /dev/null
+++ b/include/sand.h
@@ -0,0 +1,114 @@
+#ifndef SAND_H
+#define SAND_H
+
+#include <cstdint>
+#include <string>
+#include <unordered_map>
+#include <vector>
+
+namespace sand
+{
+
+struct type
+{
+  uint16_t id;
+  uint16_t default_result;
+};
+using type_map = std::unordered_map<std::string, type>;
+
+class RulesBuilder;
+class TypeBuilder
+{
+  friend RulesBuilder;
+
+public:
+  TypeBuilder& add_type(const std::string& name);
+  TypeBuilder& add_type(const std::string& name,
+                        const std::string& default_result);
+
+  RulesBuilder finish();
+
+private:
+  uint16_t next_type_id = 0;
+  type_map types;
+}; // class TypeBuilder
+
+class Rule;
+class Sand;
+class RulesBuilder
+{
+  friend TypeBuilder;
+  friend Rule;
+  friend Sand;
+
+public:
+  Rule add_rule(const std::string& source_name, const std::string& to);
+
+  Sand build(uint16_t width, uint16_t height, const std::string& initial);
+
+private:
+  RulesBuilder(const TypeBuilder& type_builder);
+
+  void finish_rule(const Rule& rule);
+
+  type_map types;
+  std::unordered_map<uint16_t,
+                     std::vector<std::pair<unsigned __int128, uint16_t>>>
+    rules;
+}; // class RulesBuilder
+
+class Rule
+{
+  friend RulesBuilder;
+
+public:
+  using match_fn = bool (*)(const std::string& name);
+
+  ~Rule();
+
+  Rule& top_left(match_fn match);
+  Rule& top_middle(match_fn match);
+  Rule& top_right(match_fn match);
+  Rule& middle_left(match_fn match);
+  Rule& middle_right(match_fn match);
+  Rule& bottom_left(match_fn match);
+  Rule& bottom_middle(match_fn match);
+  Rule& bottom_right(match_fn match);
+
+private:
+  Rule(RulesBuilder& builder, uint16_t source, uint16_t to);
+
+  RulesBuilder& builder;
+  uint16_t source;
+  uint16_t to;
+  match_fn matches[8];
+}; // class RuleBuilder
+
+class Sand
+{
+  friend RulesBuilder;
+
+public:
+  void set(uint16_t x, uint16_t y, const std::string& type);
+  uint16_t get(uint16_t x, uint16_t y);
+
+  void update();
+
+private:
+  Sand(const RulesBuilder& builder, uint16_t width, uint16_t height,
+       const std::string& initial);
+
+  uint16_t width;
+  uint16_t height;
+  type_map types;
+  std::unordered_map<uint16_t, uint16_t> default_conversions;
+  std::unordered_map<uint16_t,
+                     std::vector<std::pair<unsigned __int128, uint16_t>>>
+    rules;
+  std::vector<uint16_t> elements;
+  bool iter;
+}; // class Sand
+
+} // namespace sand
+
+#endif // SAND_H
diff --git a/src/lualib.cpp b/src/lualib.cpp
new file mode 100644
index 0000000..71193b7
--- /dev/null
+++ b/src/lualib.cpp
@@ -0,0 +1,12 @@
+#ifdef __cplusplus
+extern "C"
+{
+#endif // __cplusplus
+
+#include <luajit.h>
+
+#ifdef __cplusplus
+}
+#endif // __cplusplus
+
+extern "C" int luaopen_sand(lua_State* state) { return 1; }
diff --git a/src/main.cpp b/src/main.cpp
new file mode 100644
index 0000000..1e300b7
--- /dev/null
+++ b/src/main.cpp
@@ -0,0 +1,83 @@
+#include <SDL3/SDL.h>
+#include <SDL3/SDL_events.h>
+#include <SDL3/SDL_mouse.h>
+#include <SDL3/SDL_oldnames.h>
+#include <SDL3/SDL_surface.h>
+#include <SDL3/SDL_timer.h>
+#include <SDL3/SDL_video.h>
+#include <sand.h>
+
+uint8_t lookup[][3]
+  = { { 0, 0, 0 }, { 50, 0, 0 }, { 100, 100, 100 }, { 200, 200, 200 } };
+
+int main(int argc, char** argv)
+{
+  auto rb = sand::TypeBuilder()
+              .add_type("offgrid")
+              .add_type("air")
+              .add_type("stone1")
+              .add_type("stone2")
+              .finish();
+
+  rb.add_rule("air", "stone1")
+    .top_middle([](const auto& t) { return t == "stone1"; });
+
+  rb.add_rule("stone1", "air")
+    .top_middle([](const auto& t) { return t == "air" || t == "offgrid"; })
+    .bottom_middle([](const auto& t) { return t == "air"; });
+
+  auto s = rb.build(64, 64, "air");
+
+  SDL_Init(SDL_INIT_VIDEO);
+  SDL_Window* window = SDL_CreateWindow("sand test", 512, 512, 0);
+  SDL_Surface* surface = SDL_CreateSurface(64, 64, SDL_PIXELFORMAT_RGB24);
+
+  int prev_ms = SDL_GetTicks();
+  float time = 0;
+  bool cont = true;
+  while (cont)
+  {
+    SDL_Event e;
+    while (SDL_PollEvent(&e))
+    {
+      if (e.type == SDL_EVENT_QUIT)
+      {
+        cont = false;
+      }
+    }
+
+    int ms = SDL_GetTicks();
+    float dt = (ms - prev_ms) / 1000.0f;
+    prev_ms = ms;
+    time += dt;
+
+    float x, y;
+    int state;
+    if (time > 0.008 && (state = SDL_GetMouseState(&x, &y)))
+    {
+      time = 0;
+      s.set(x * 64 / 512, y * 64 / 512, state == 1 ? "stone1" : "stone2");
+    }
+
+    SDL_LockSurface(surface);
+    for (int i = 0; i < 64; i++)
+    {
+      for (int j = 0; j < 64; j++)
+      {
+        memcpy(&static_cast<uint8_t*>(surface->pixels)[3 * (i + j * 64)],
+               lookup[s.get(i, j)], 3);
+      }
+    }
+    SDL_UnlockSurface(surface);
+    SDL_BlitSurfaceScaled(surface, nullptr, SDL_GetWindowSurface(window),
+                          nullptr, SDL_SCALEMODE_NEAREST);
+    SDL_UpdateWindowSurface(window);
+
+    s.update();
+  }
+
+  SDL_DestroyWindow(window);
+  SDL_Quit();
+
+  return 0;
+}
diff --git a/src/sand.cpp b/src/sand.cpp
new file mode 100644
index 0000000..81f8ead
--- /dev/null
+++ b/src/sand.cpp
@@ -0,0 +1,344 @@
+#include "sand.h"
+
+#include <algorithm>
+#include <cstdint>
+
+using namespace sand;
+
+namespace
+{
+
+template <typename T>
+T& binary_search(T element, T* elements, size_t begin, size_t end,
+                 auto (*fn)(T, T)->bool)
+{
+  if (end - begin == 1)
+  {
+    return elements[begin];
+  }
+
+  size_t index = begin + (end - begin) / 2;
+
+  if (!fn(element, elements[index]) && !fn(elements[index], element))
+  {
+    return elements[index];
+  }
+  else if (fn(element, elements[index]))
+  {
+    return binary_search<T>(element, elements, index, end, fn);
+  }
+  else
+  {
+    return binary_search<T>(element, elements, begin, index, fn);
+  }
+}
+
+} // namespace
+
+TypeBuilder& TypeBuilder::add_type(const std::string& name)
+{
+  if (!types.contains(name))
+  {
+    types[name] = { .id = next_type_id, .default_result = next_type_id };
+    next_type_id += 1;
+  }
+
+  return *this;
+}
+
+TypeBuilder& TypeBuilder::add_type(const std::string& name,
+                                   const std::string& default_result)
+{
+  add_type(name);
+  add_type(default_result);
+
+  types[name].default_result = types[default_result].id;
+
+  return *this;
+}
+
+RulesBuilder TypeBuilder::finish() { return RulesBuilder(*this); }
+
+Rule RulesBuilder::add_rule(const std::string& name, const std::string& to)
+{
+  return Rule(*this, types[name].id, types[to].id);
+}
+
+Sand RulesBuilder::build(uint16_t width, uint16_t height,
+                         const std::string& initial)
+{
+  for (auto& [key, rule] : rules)
+  {
+    std::sort(rule.begin(), rule.end(),
+              [](auto a, auto b) { return a.first < b.first; });
+  }
+  return Sand(*this, width, height, initial);
+}
+
+RulesBuilder::RulesBuilder(const TypeBuilder& type_builder) :
+  types(type_builder.types)
+{
+}
+
+void RulesBuilder::finish_rule(const Rule& rule)
+{
+  // 8 nested loops is kinda silly, maybe there's a better way to do this?
+  // top left
+  for (const auto& [tl_name, tl_type] : types)
+  {
+    if (!rule.matches[0] || rule.matches[0](tl_name))
+    {
+      // top middle
+      for (const auto& [tm_name, tm_type] : types)
+      {
+        if (!rule.matches[1] || rule.matches[1](tm_name))
+        {
+          // top right
+          for (const auto& [tr_name, tr_type] : types)
+          {
+            if (!rule.matches[2] || rule.matches[2](tr_name))
+            {
+              // middle left
+              for (const auto& [ml_name, ml_type] : types)
+              {
+                if (!rule.matches[3] || rule.matches[3](ml_name))
+                {
+                  // middle right
+                  for (const auto& [mr_name, mr_type] : types)
+                  {
+                    if (!rule.matches[4] || rule.matches[4](mr_name))
+                    {
+                      // bottom left
+                      for (const auto& [bl_name, bl_type] : types)
+                      {
+                        if (!rule.matches[5] || rule.matches[5](bl_name))
+                        {
+                          // bottom middle
+                          for (const auto& [bm_name, bm_type] : types)
+                          {
+                            if (!rule.matches[6] || rule.matches[6](bm_name))
+                            {
+                              // bottom right
+                              for (const auto& [br_name, br_type] : types)
+                              {
+                                if (!rule.matches[7]
+                                    || rule.matches[7](br_name))
+                                {
+                                  unsigned __int128 neighbors = 0;
+
+                                  neighbors += tl_type.id;
+                                  neighbors <<= 16;
+
+                                  neighbors += tm_type.id;
+                                  neighbors <<= 16;
+
+                                  neighbors += tr_type.id;
+                                  neighbors <<= 16;
+
+                                  neighbors += ml_type.id;
+                                  neighbors <<= 16;
+
+                                  neighbors += mr_type.id;
+                                  neighbors <<= 16;
+
+                                  neighbors += bl_type.id;
+                                  neighbors <<= 16;
+
+                                  neighbors += bm_type.id;
+                                  neighbors <<= 16;
+
+                                  neighbors += br_type.id;
+
+                                  if (!rules.contains(rule.source))
+                                  {
+                                    rules[rule.source] = {};
+                                  }
+
+                                  rules[rule.source].push_back(
+                                    { neighbors, rule.to });
+                                }
+                              }
+                            }
+                          }
+                        }
+                      }
+                    }
+                  }
+                }
+              }
+            }
+          }
+        }
+      }
+    }
+  }
+}
+
+Rule::~Rule() { builder.finish_rule(*this); }
+
+Rule& Rule::top_left(match_fn match)
+{
+  matches[0] = match;
+
+  return *this;
+}
+
+Rule& Rule::top_middle(match_fn match)
+{
+  matches[1] = match;
+
+  return *this;
+}
+
+Rule& Rule::top_right(match_fn match)
+{
+  matches[2] = match;
+
+  return *this;
+}
+
+Rule& Rule::middle_left(match_fn match)
+{
+  matches[3] = match;
+
+  return *this;
+}
+
+Rule& Rule::middle_right(match_fn match)
+{
+  matches[4] = match;
+
+  return *this;
+}
+
+Rule& Rule::bottom_left(match_fn match)
+{
+  matches[5] = match;
+
+  return *this;
+}
+
+Rule& Rule::bottom_middle(match_fn match)
+{
+  matches[6] = match;
+
+  return *this;
+}
+
+Rule& Rule::bottom_right(match_fn match)
+{
+  matches[7] = match;
+
+  return *this;
+}
+
+Rule::Rule(RulesBuilder& builder, uint16_t source, uint16_t to) :
+  builder(builder),
+  source(source),
+  to(to),
+  matches{}
+{
+}
+
+Sand::Sand(const RulesBuilder& builder, uint16_t width, uint16_t height,
+           const std::string& initial) :
+  width(width),
+  height(height),
+  types(builder.types),
+  rules(builder.rules),
+  elements(width * height * 2, types[initial].id),
+  iter(false)
+{
+  for (const auto& [name, type] : types)
+  {
+    default_conversions[type.id] = type.default_result;
+  }
+}
+
+void Sand::set(uint16_t x, uint16_t y, const std::string& type)
+{
+  elements[x + y * width + iter * width * height] = types[type].id;
+}
+
+uint16_t Sand::get(uint16_t x, uint16_t y)
+{
+  return elements[x + y * width + iter * width * height];
+}
+
+void Sand::update()
+{
+  for (uint32_t i = 0; i < width; i++)
+  {
+    for (uint32_t j = 0; j < height; j++)
+    {
+      auto& current_rule = rules[get(i, j)];
+
+      unsigned __int128 neighbors = 0;
+      if (i > 0 && j > 0)
+      {
+        neighbors += get(i - 1, j - 1);
+      }
+      neighbors <<= 16;
+
+      if (j > 0)
+      {
+        neighbors += get(i, j - 1);
+      }
+      neighbors <<= 16;
+
+      if (i < width - 1 && j > 0)
+      {
+        neighbors += get(i + 1, j);
+      }
+      neighbors <<= 16;
+
+      if (i > 0)
+      {
+        neighbors += get(i - 1, j);
+      }
+      neighbors <<= 16;
+
+      if (i < width - 1)
+      {
+        neighbors += get(i + 1, j);
+      }
+      neighbors <<= 16;
+
+      if (i > 0 && j < height - 1)
+      {
+        neighbors += get(i - 1, j + 1);
+      }
+      neighbors <<= 16;
+
+      if (j < height - 1)
+      {
+        neighbors += get(i, j + 1);
+      }
+      neighbors <<= 16;
+
+      if (i < width - 1 && j < height - 1)
+      {
+        neighbors += get(i + 1, j + 1);
+      }
+
+      uint16_t result = default_conversions[get(i, j)];
+      if (!current_rule.empty())
+      {
+        std::pair<unsigned __int128, uint16_t> element = { neighbors, 0 };
+        bool (*fn)(decltype(element), decltype(element))
+          = [](decltype(element) a, decltype(element) b) -> bool
+        { return a.first > b.first; };
+        const auto& found = binary_search(element, current_rule.data(), 0,
+                                          current_rule.size(), fn);
+        if (found.first == neighbors)
+        {
+          result = found.second;
+        }
+      }
+
+      elements[i + j * width + !iter * width * height] = result;
+    }
+  }
+
+  iter = !iter;
+}