diff --git a/src/game.c b/src/game.c
new file mode 100644
index 0000000..9ec951b
--- /dev/null
+++ b/src/game.c
@@ -0,0 +1,57 @@
+#include "ok_game.h"
+#include "ok_map.h"
+#include "ok_unit.h"
+#include <string.h>
+
+void ok_game_spawn(OkGame *g, OkFaction f, OkUnitKind k, int x, int y) {
+  if (g->unit_count >= OK_MAX_UNITS) return;
+  if (!ok_map_walkable(&g->map, x, y)) return;
+  OkUnit *u = &g->units[g->unit_count++];
+  memset(u, 0, sizeof(*u));
+  u->x = x;
+  u->y = y;
+  u->faction = f;
+  u->kind = k;
+  u->hp_max = (k == OK_UNIT_VEHICLE) ? 80 : 30;
+  u->hp = u->hp_max;
+  u->target = -1;
+  u->alive = true;
+}
+
+void ok_game_init(OkGame *g) {
+  memset(g, 0, sizeof(*g));
+  ok_map_generate(&g->map);
+  g->selected = -1;
+  g->running = true;
+  /* two camps */
+  ok_game_spawn(g, OK_FACTION_SURVIVORS, OK_UNIT_INFANTRY, 6, 6);
+  ok_game_spawn(g, OK_FACTION_SURVIVORS, OK_UNIT_VEHICLE, 8, 6);
+  ok_game_spawn(g, OK_FACTION_SCAVENGERS, OK_UNIT_INFANTRY, OK_MAP_W - 8, OK_MAP_H - 8);
+  ok_game_spawn(g, OK_FACTION_SCAVENGERS, OK_UNIT_VEHICLE, OK_MAP_W - 10, OK_MAP_H - 8);
+  /* auto-aggro first pair */
+  if (g->unit_count >= 4) {
+    g->units[0].target = 2;
+    g->units[1].target = 3;
+    g->units[2].target = 0;
+    g->units[3].target = 1;
+  }
+}
+
+void ok_game_update(OkGame *g, float dt) {
+  if (!g->running) return;
+  g->tick++;
+  ok_units_update(g, dt);
+  int s_alive = 0, c_alive = 0;
+  for (int i = 0; i < g->unit_count; i++) {
+    if (!g->units[i].alive) continue;
+    if (g->units[i].faction == OK_FACTION_SURVIVORS) s_alive++;
+    else c_alive++;
+  }
+  if (s_alive == 0) {
+    g->scavengers_win = true;
+    g->running = false;
+  } else if (c_alive == 0) {
+    g->survivors_win = true;
+    g->running = false;
+  }
+}
diff --git a/src/main.c b/src/main.c
new file mode 100644
index 0000000..b57b889
--- /dev/null
+++ b/src/main.c
@@ -0,0 +1,44 @@
+#include "ok_game.h"
+#include "ok_render.h"
+#include <stdio.h>
+#include <SDL.h>
+
+#ifndef OPENKKND_VERSION
+#define OPENKKND_VERSION "dev"
+#endif
+
+int main(int argc, char **argv) {
+  (void)argc;
+  (void)argv;
+  printf("OpenKKND %s — original genre RTS (MIT). No commercial IP assets.\n", OPENKKND_VERSION);
+
+  const int tw = 12;
+  if (!ok_render_init(OK_MAP_W * tw, OK_MAP_H * tw)) {
+    fprintf(stderr, "render init failed\n");
+    return 1;
+  }
+
+  OkGame game;
+  ok_game_init(&game);
+
+  Uint64 prev = SDL_GetPerformanceCounter();
+  const Uint64 freq = SDL_GetPerformanceFrequency();
+
+  while (game.running || true) {
+    SDL_Event e;
+    while (SDL_PollEvent(&e)) {
+      if (e.type == SDL_QUIT) goto done;
+      if (e.type == SDL_KEYDOWN && e.key.keysym.sym == SDLK_ESCAPE) goto done;
+      if (e.type == SDL_KEYDOWN && e.key.keysym.sym == SDLK_r) ok_game_init(&game);
+    }
+    Uint64 now = SDL_GetPerformanceCounter();
+    float dt = (float)(now - prev) / (float)freq;
+    prev = now;
+    if (dt > 0.05f) dt = 0.05f;
+    if (game.running) ok_game_update(&game, dt);
+    ok_render_draw(&game);
+  }
+done:
+  ok_render_shutdown();
+  return 0;
+}
diff --git a/src/map.c b/src/map.c
new file mode 100644
index 0000000..c372d83
--- /dev/null
+++ b/src/map.c
@@ -0,0 +1,19 @@
+#include "ok_map.h"
+#include <stdlib.h>
+
+void ok_map_generate(OkMap *m) {
+  for (int y = 0; y < OK_MAP_H; y++) {
+    for (int x = 0; x < OK_MAP_W; x++) {
+      m->tile[y][x] = 0;
+      if (x == 0 || y == 0 || x == OK_MAP_W - 1 || y == OK_MAP_H - 1)
+        m->tile[y][x] = 1;
+      else if ((x * 17 + y * 31) % 47 == 0)
+        m->tile[y][x] = 2; /* scrap pile */
+    }
+  }
+}
+
+bool ok_map_walkable(const OkMap *m, int x, int y) {
+  if (x < 0 || y < 0 || x >= OK_MAP_W || y >= OK_MAP_H) return false;
+  return m->tile[y][x] != 1;
+}
diff --git a/src/render.c b/src/render.c
new file mode 100644
index 0000000..f8a5bcc
--- /dev/null
+++ b/src/render.c
@@ -0,0 +1,71 @@
+#include "ok_render.h"
+#include <stdio.h>
+
+static SDL_Window *win;
+static SDL_Renderer *ren;
+static int tile = 12;
+
+bool ok_render_init(int w, int h) {
+  if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_TIMER) != 0) {
+    fprintf(stderr, "SDL_Init: %s\n", SDL_GetError());
+    return false;
+  }
+  win = SDL_CreateWindow("OpenKKND " OPENKKND_VERSION,
+                         SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
+                         w, h, SDL_WINDOW_SHOWN);
+  if (!win) return false;
+  ren = SDL_CreateRenderer(win, -1, SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC);
+  if (!ren) ren = SDL_CreateRenderer(win, -1, 0);
+  return ren != NULL;
+}
+
+SDL_Window *ok_render_window(void) { return win; }
+
+void ok_render_draw(const OkGame *g) {
+  SDL_SetRenderDrawColor(ren, 20, 18, 16, 255);
+  SDL_RenderClear(ren);
+  for (int y = 0; y < OK_MAP_H; y++) {
+    for (int x = 0; x < OK_MAP_W; x++) {
+      uint8_t t = g->map.tile[y][x];
+      if (t == 1) SDL_SetRenderDrawColor(ren, 50, 45, 40, 255);
+      else if (t == 2) SDL_SetRenderDrawColor(ren, 90, 70, 30, 255);
+      else SDL_SetRenderDrawColor(ren, 35, 40, 32, 255);
+      SDL_Rect r = {x * tile, y * tile, tile - 1, tile - 1};
+      SDL_RenderFillRect(ren, &r);
+    }
+  }
+  for (int i = 0; i < g->unit_count; i++) {
+    const OkUnit *u = &g->units[i];
+    if (!u->alive) continue;
+    if (u->faction == OK_FACTION_SURVIVORS)
+      SDL_SetRenderDrawColor(ren, 60, 160, 220, 255);
+    else
+      SDL_SetRenderDrawColor(ren, 220, 90, 50, 255);
+    int s = (u->kind == OK_UNIT_VEHICLE) ? tile : tile - 3;
+    SDL_Rect r = {u->x * tile + 1, u->y * tile + 1, s, s};
+    SDL_RenderFillRect(ren, &r);
+    /* hp bar */
+    SDL_SetRenderDrawColor(ren, 0, 0, 0, 255);
+    SDL_Rect bg = {r.x, r.y - 3, s, 2};
+    SDL_RenderFillRect(ren, &bg);
+    int hw = s * u->hp / (u->hp_max ? u->hp_max : 1);
+    SDL_SetRenderDrawColor(ren, 40, 200, 60, 255);
+    SDL_Rect hg = {r.x, r.y - 3, hw, 2};
+    SDL_RenderFillRect(ren, &hg);
+  }
+  if (!g->running) {
+    if (g->survivors_win) SDL_SetRenderDrawColor(ren, 40, 180, 255, 180);
+    else SDL_SetRenderDrawColor(ren, 255, 80, 40, 180);
+    SDL_Rect banner = {0, (OK_MAP_H * tile) / 2 - 20, OK_MAP_W * tile, 40};
+    SDL_RenderFillRect(ren, &banner);
+  }
+  SDL_RenderPresent(ren);
+}
+
+void ok_render_shutdown(void) {
+  if (ren) SDL_DestroyRenderer(ren);
+  if (win) SDL_DestroyWindow(win);
+  ren = NULL;
+  win = NULL;
+  SDL_Quit();
+}
diff --git a/src/unit.c b/src/unit.c
new file mode 100644
index 0000000..5e536f3
--- /dev/null
+++ b/src/unit.c
@@ -0,0 +1,37 @@
+#include "ok_unit.h"
+#include "ok_map.h"
+#include <math.h>
+
+static int dist2(int ax, int ay, int bx, int by) {
+  int dx = ax - bx, dy = ay - by;
+  return dx * dx + dy * dy;
+}
+
+void ok_units_update(OkGame *g, float dt) {
+  (void)dt;
+  for (int i = 0; i < g->unit_count; i++) {
+    OkUnit *u = &g->units[i];
+    if (!u->alive) continue;
+    if (u->target < 0 || u->target >= g->unit_count) continue;
+    OkUnit *t = &g->units[u->target];
+    if (!t->alive || t->faction == u->faction) {
+      u->target = -1;
+      continue;
+    }
+    int range = (u->kind == OK_UNIT_VEHICLE) ? 8 : 4;
+    if (dist2(u->x, u->y, t->x, t->y) <= range * range) {
+      int dmg = (u->kind == OK_UNIT_VEHICLE) ? 4 : 2;
+      t->hp -= dmg;
+      if (t->hp <= 0) {
+        t->alive = false;
+        t->hp = 0;
+      }
+    } else {
+      /* crude step toward target */
+      int nx = u->x + (t->x > u->x) - (t->x < u->x);
+      int ny = u->y + (t->y > u->y) - (t->y < u->y);
+      if (ok_map_walkable(&g->map, nx, u->y)) u->x = nx;
+      if (ok_map_walkable(&g->map, u->x, ny)) u->y = ny;
+    }
+  }
+}