feat: add temporary hazardous barriers in hard mode

AGENTS.md

@@ -102,8 +102,9 @@ The game operates in one of two scenes ([`Scene`](include/game_state.h#L9-L12)):
 
 ### 3.4 Game Modes & Progressive Speed Mechanics
 - **Normal Mode:** Starts with length 4, base timer frequency 5.0 Hz (`SPEED_BASE_NORMAL_MHZ = 5000`), scaling up to 13.0 Hz (`SPEED_MAX_NORMAL_MHZ = 13000`).
-- **Hard Mode:** Starts with length 2, base timer frequency 9.0 Hz (`SPEED_BASE_HARD_MHZ = 9000`), scaling up to 17.0 Hz (`SPEED_MAX_HARD_MHZ = 17000`), and spawns rotten apples.
-- **Progressive Speed Scaling:** Each consumed regular apple increases `state.applesEaten`. Game speed scales linearly with consumed apples up to `SPEED_APPLES_CAP = 40`, granting smooth +200 mHz acceleration per apple. Timer 0 reload registers are recomputed on the fly (`calculate_timer_reload()`).
+- **Hard Mode:** Starts with length 2, base timer frequency 5.0 Hz (`SPEED_BASE_HARD_MHZ = 5000`, matching Normal Mode's starting speed), scaling up to 17.0 Hz (`SPEED_MAX_HARD_MHZ = 17000`), spawns rotten apples, and spawns temporary fatal barriers.
+- **Temporary Fatal Barriers (Hard Mode):** Straight lines of blocks appear dynamically across the playfield without overlapping the snake or apples. Barriers only begin spawning after a few apples have been eaten (`BARRIER_START_APPLES = 3`). Their maximum possible length begins at 4 blocks (`BARRIER_BASE_MAX_LENGTH`) and gradually scales up to 10 blocks (`BARRIER_MAX_LENGTH`) later on in the game. At later stages of the game, multiple barriers can spawn simultaneously in a single spawn event (up to 2 at once starting at 16 apples, and up to 3 at once starting at 30 apples), synchronizing their warning and activation phases. Before becoming lethal, each barrier announces itself with a flashing warning reticle frame (`BARRIER_WARN_FRAMES = 120` frames / 2.0 s) whose pulse frequency accelerates and warning color intensifies from dim orange to incandescent yellow-white as solidification approaches. Once active, barriers turn into solid hazard-striped energy walls (`BARRIER_ACTIVE_FRAMES = 240` frames / 4.0 s) fatal to the snake's head on contact. As apples are eaten, spawn intervals accelerate from 9.0 s down to 2.0 s (`BARRIER_INTERVAL_MAX_FRAMES` to `BARRIER_INTERVAL_MIN_FRAMES`) and max concurrent barriers scale up from 1 to 4 (`BARRIER_MAX_COUNT`).
+- **Progressive Speed Scaling:** Each consumed regular apple increases `state.applesEaten`. Game speed scales linearly with consumed apples up to `SPEED_APPLES_CAP = 40`, granting smooth +200 mHz acceleration per apple (or +300 mHz in Hard Mode). Timer 0 reload registers are recomputed on the fly (`calculate_timer_reload()`).
 - **Progressive Background Intensity Scaling:** Visual effects intensify at the exact same rate (`calculate_intensity_31()`):
   - Hardware drift scroll speeds accelerate on both top and bottom screens.
   - Celestial node oscillation & twinkling breathing frequencies increase via fixed-point phase accumulation (`anim_phase_fp`).

include/consts.h

@@ -1,6 +1,7 @@
 #ifndef CONSTS_H
 #define CONSTS_H
-#endif
+
+#include <cstdint>
 
 const int START_LENGTH = 4;
 const int START_LENGTH_HARD = 2;
@@ -14,9 +15,36 @@ const uint16_t CURSE_PAL_GLOW    = 18;
 const uint16_t CURSE_PAL_CORE    = 19;
 const uint16_t CURSE_PAL_LEAF    = 20;
 
+// Barrier palette indices in SPRITE_PALETTE_SUB (animated every VBlank)
+const uint16_t BARRIER_PAL_EDGE   = 21;
+const uint16_t BARRIER_PAL_FILL   = 22;
+const uint16_t BARRIER_PAL_STRIPE = 23;
+const uint16_t BARRIER_PAL_WARN   = 24;
+
+// Hard-mode temporary fatal barriers (all timings in 60 Hz VBlank frames,
+// so they stay constant in wall-clock time while the tick rate accelerates)
+const int BARRIER_START_APPLES          = 3;   // Barriers only start appearing after eating a few apples
+const int BARRIER_MULTI_SPAWN_APPLES_2  = 16;  // Apples required to spawn up to 2 barriers at once
+const int BARRIER_MULTI_SPAWN_APPLES_3  = 30;  // Apples required to spawn up to 3 barriers at once
+const int BARRIER_MAX_COUNT             = 4;   // Max simultaneous barriers (reached at SPEED_APPLES_CAP)
+const int BARRIER_MIN_LENGTH         = 2;
+const int BARRIER_BASE_MAX_LENGTH    = 4;   // Max length when barriers first appear
+const int BARRIER_MAX_LENGTH         = 10;  // Max length later in the game (reached at SPEED_APPLES_CAP)
+const int BARRIER_OAM_SLOTS          = BARRIER_MAX_COUNT * BARRIER_MAX_LENGTH; // Reserved OAM ids 0..39
+const int BARRIER_WARN_FRAMES        = 120; // 2.0 s flashing announcement (harmless)
+const int BARRIER_SOLIDIFY_FRAMES    = 20;  // Last part of warning: flickers to solid look
+const int BARRIER_ACTIVE_FRAMES      = 240; // 4.0 s fatal phase
+const int BARRIER_FADE_FRAMES        = 45;  // Last part of active phase: slow blink (still fatal)
+const int BARRIER_FIRST_SPAWN_FRAMES = 180; // 3.0 s grace period after reaching BARRIER_START_APPLES
+const int BARRIER_INTERVAL_MAX_FRAMES = 540; // 9.0 s between spawns at BARRIER_START_APPLES
+const int BARRIER_INTERVAL_MIN_FRAMES = 120; // 2.0 s between spawns at SPEED_APPLES_CAP
+const int BARRIER_INTERVAL_JITTER    = 60;  // Random 0..1 s extra delay
+const int BARRIER_RETRY_FRAMES       = 30;  // Retry delay if no valid spot was found
+const int BARRIER_HEAD_SAFE_DISTANCE = 5;   // Min wrapped Manhattan distance from the snake head
+
 // Speed scaling configuration (gradual acceleration based on consumed apples)
 const int SPEED_BASE_NORMAL_MHZ = 5000;  // 5.0 Hz (~200 ms per step)
-const int SPEED_BASE_HARD_MHZ   = 9000;  // 9.0 Hz (~111 ms per step)
+const int SPEED_BASE_HARD_MHZ   = 5000;  // 5.0 Hz: hard mode starts as slow as normal mode
 const int SPEED_MAX_NORMAL_MHZ  = 13000; // 13.0 Hz (~77 ms per step)
 const int SPEED_MAX_HARD_MHZ    = 17000; // 17.0 Hz (~59 ms per step)
 const int SPEED_APPLES_CAP      = 40;    // Apples consumed to reach max intensity & speed
@@ -70,3 +98,5 @@ const char BITMAP_SEGMENT[] = {
         5,6,6,6,6,6,6,5,
         0,5,5,5,5,5,5,0
 	};
+
+#endif // CONSTS_H

include/game_logic.h

@@ -17,4 +17,14 @@ uint8_t calculate_intensity_31(const GameState &state);
 uint16_t calculate_timer_freq_mhz(const GameState &state);
 uint16_t calculate_timer_reload(const GameState &state);
 
+// Hard-mode temporary barriers
+void reset_barriers(GameState &state);              // Main thread (init_game)
+void tick_barriers_frame(GameState &state);         // VBlank IRQ: advances lifetimes
+void spawn_barriers(GameState &state);              // Timer IRQ: spawns when cooldown expired
+bool check_collision_barriers(GameState &state);    // Timer IRQ: head vs. active barrier
+bool is_barrier_cell(const GameState &state, int x, int y, bool include_warning);
+uint16_t calculate_barrier_interval_frames(const GameState &state);
+uint8_t calculate_barrier_max_length(const GameState &state);
+uint8_t calculate_barrier_max_batch(const GameState &state);
+
 #endif

include/game_render.h

@@ -32,6 +32,8 @@ struct RenderAssets {
     u16 *gfx_tail_v[2] = {nullptr, nullptr};
     u16 *gfx_apple_rotten = nullptr;
     u16 *gfx_apple_cursed = nullptr;
+    u16 *gfx_barrier = nullptr;      // Solid, fatal barrier segment
+    u16 *gfx_barrier_warn = nullptr; // Dashed outline shown while announcing
 
     HudCache hudCache;
 };
@@ -41,5 +43,7 @@ void draw_game(const GameState &state, const RenderAssets &assets);
 void draw_stats(const GameState &state, RenderAssets &assets, bool internals, bool musicEnabled, uint8_t frame);
 void draw_menu(const GameState &state, RenderAssets &assets, bool musicEnabled);
 void blink_apples(const GameState &state, u16 *gfx_apple);
+// Called every VBlank: owns OAM slots [0, BARRIER_OAM_SLOTS) and animates barrier palette entries
+void draw_barriers(const GameState &state, const RenderAssets &assets, uint8_t frame);
 
 #endif

include/game_state.h

@@ -6,6 +6,8 @@
 #include <vector>
 #include <nds/ndstypes.h>
 
+#include "consts.h"
+
 enum class Scene {
     Menu,
     Playing,
@@ -13,6 +15,23 @@ enum class Scene {
 
 constexpr int MENU_ITEM_COUNT = 3;
 
+enum class BarrierPhase : uint8_t {
+    Inactive, // Slot free
+    Warning,  // Flashing announcement, harmless
+    Active,   // Solid and fatal to the snake head
+};
+
+// Temporary hard-mode wall: a straight line of `length` cells starting at (x, y).
+// Lifetime is tracked in VBlank frames (see tick_barriers_frame()).
+struct Barrier {
+    BarrierPhase phase = BarrierPhase::Inactive;
+    int8_t x = 0;
+    int8_t y = 0;
+    bool vertical = false;
+    uint8_t length = 0;
+    uint16_t framesLeft = 0; // Frames remaining in the current phase
+};
+
 struct GameState {
     volatile uint16_t ticks = 0;
     volatile uint16_t snakelength = 0;
@@ -29,6 +48,11 @@ struct GameState {
 
     uint16_t curseTicksRemaining = 0;
 
+    // Fixed-size (no heap) because barriers are touched from both the VBlank
+    // and Timer 0 IRQs. Those IRQs don't nest, so no further locking is needed.
+    std::array<Barrier, BARRIER_MAX_COUNT> barriers{};
+    volatile uint16_t barrierSpawnCooldown = 0; // Frames until the next spawn attempt
+
     std::deque<std::array<int, 3>> snake;
     std::vector<std::array<int, 2>> apples;
     std::vector<std::array<int, 2>> bad_apples;

source/game_logic.cpp

@@ -114,8 +114,14 @@ bool check_collision_apples_cursed(GameState &state) {
 }
 
 void spawn_apples(GameState &state) {
-  if (state.apples.size() < 1) {
+  if (state.apples.empty()) {
     std::array<int, 2> apple = {rand() % (X_MAX + 1), rand() % (Y_MAX + 1)};
+    // Don't place the apple inside a (pending) barrier, it would be unreachable
+    for (int attempt = 0;
+         attempt < 16 && is_barrier_cell(state, apple[0], apple[1], true);
+         attempt++) {
+      apple = {rand() % (X_MAX + 1), rand() % (Y_MAX + 1)};
+    }
     state.apples.push_back(apple);
   }
 }
@@ -172,3 +178,245 @@ uint16_t calculate_timer_reload(const GameState &state) {
   const uint32_t period_ticks = timer_clock_mhz / freq_mhz;
   return static_cast<uint16_t>(-static_cast<int32_t>(period_ticks));
 }
+
+// ---------------------------------------------------------------------------
+// Hard-mode temporary barriers
+// ---------------------------------------------------------------------------
+
+namespace {
+
+bool barrier_contains(const Barrier &barrier, int x, int y) {
+  if (barrier.vertical) {
+    return x == barrier.x && y >= barrier.y && y < barrier.y + barrier.length;
+  }
+  return y == barrier.y && x >= barrier.x && x < barrier.x + barrier.length;
+}
+
+// Manhattan distance on the wrapping playfield
+int wrapped_distance(int x1, int y1, int x2, int y2) {
+  int dx = std::abs(x1 - x2);
+  int dy = std::abs(y1 - y2);
+  dx = std::min(dx, (X_MAX + 1) - dx);
+  dy = std::min(dy, (Y_MAX + 1) - dy);
+  return dx + dy;
+}
+
+bool cell_in_list(const std::vector<std::array<int, 2>> &list, int x, int y) {
+  return std::any_of(list.begin(), list.end(),
+                     [&](const std::array<int, 2> &item) {
+                       return item[0] == x && item[1] == y;
+                     });
+}
+
+bool cell_blocked_for_barrier(const GameState &state, int x, int y) {
+  if (is_barrier_cell(state, x, y, true)) {
+    return true;
+  }
+  if (cell_in_list(state.apples, x, y) || cell_in_list(state.bad_apples, x, y) ||
+      cell_in_list(state.cursed_apples, x, y)) {
+    return true;
+  }
+  if (!state.snake.empty()) {
+    const auto &head = state.snake.front();
+    if (wrapped_distance(head[0], head[1], x, y) < BARRIER_HEAD_SAFE_DISTANCE) {
+      return true;
+    }
+  }
+  return std::any_of(state.snake.begin(), state.snake.end(),
+                     [&](const std::array<int, 3> &seg) {
+                       return seg[0] == x && seg[1] == y;
+                     });
+}
+
+int max_concurrent_barriers(const GameState &state) {
+  if (state.applesEaten < BARRIER_START_APPLES) {
+    return 0;
+  }
+  const int apples = std::min<int>(state.applesEaten, SPEED_APPLES_CAP);
+  const int apple_span = SPEED_APPLES_CAP - BARRIER_START_APPLES;
+  if (apple_span <= 0) {
+    return BARRIER_MAX_COUNT;
+  }
+  const int progress = apples - BARRIER_START_APPLES;
+  return 1 + ((progress * (BARRIER_MAX_COUNT - 1)) / apple_span);
+}
+
+} // namespace
+
+void reset_barriers(GameState &state) {
+  // Called from the main thread; keep the VBlank/Timer IRQs out while resetting
+  const int old_ime = enterCriticalSection();
+  for (Barrier &barrier : state.barriers) {
+    barrier = Barrier{};
+  }
+  state.barrierSpawnCooldown = BARRIER_FIRST_SPAWN_FRAMES;
+  leaveCriticalSection(old_ime);
+}
+
+bool is_barrier_cell(const GameState &state, int x, int y,
+                     bool include_warning) {
+  return std::any_of(
+      state.barriers.begin(), state.barriers.end(), [&](const Barrier &b) {
+        const bool relevant =
+            (b.phase == BarrierPhase::Active) ||
+            (include_warning && b.phase == BarrierPhase::Warning);
+        return relevant && barrier_contains(b, x, y);
+      });
+}
+
+uint8_t calculate_barrier_max_length(const GameState &state) {
+  if (state.applesEaten <= BARRIER_START_APPLES) {
+    return static_cast<uint8_t>(BARRIER_BASE_MAX_LENGTH);
+  }
+  const int apples = std::min<int>(state.applesEaten, SPEED_APPLES_CAP);
+  const int apple_span = SPEED_APPLES_CAP - BARRIER_START_APPLES;
+  if (apple_span <= 0) {
+    return static_cast<uint8_t>(BARRIER_MAX_LENGTH);
+  }
+  const int length_span = BARRIER_MAX_LENGTH - BARRIER_BASE_MAX_LENGTH;
+  const int progress = apples - BARRIER_START_APPLES;
+  return static_cast<uint8_t>(BARRIER_BASE_MAX_LENGTH +
+                              ((progress * length_span) / apple_span));
+}
+
+uint8_t calculate_barrier_max_batch(const GameState &state) {
+  if (state.applesEaten >= BARRIER_MULTI_SPAWN_APPLES_3) {
+    return 3;
+  }
+  if (state.applesEaten >= BARRIER_MULTI_SPAWN_APPLES_2) {
+    return 2;
+  }
+  return 1;
+}
+
+uint16_t calculate_barrier_interval_frames(const GameState &state) {
+  if (state.applesEaten <= BARRIER_START_APPLES) {
+    return BARRIER_INTERVAL_MAX_FRAMES;
+  }
+  const int apples = std::min<int>(state.applesEaten, SPEED_APPLES_CAP);
+  const int apple_span = SPEED_APPLES_CAP - BARRIER_START_APPLES;
+  if (apple_span <= 0) {
+    return BARRIER_INTERVAL_MIN_FRAMES;
+  }
+  const int span = BARRIER_INTERVAL_MAX_FRAMES - BARRIER_INTERVAL_MIN_FRAMES;
+  const int progress = apples - BARRIER_START_APPLES;
+  return static_cast<uint16_t>(BARRIER_INTERVAL_MAX_FRAMES -
+                               ((progress * span) / apple_span));
+}
+
+void tick_barriers_frame(GameState &state) {
+  if (state.applesEaten < BARRIER_START_APPLES) {
+    state.barrierSpawnCooldown = BARRIER_FIRST_SPAWN_FRAMES;
+    return;
+  }
+
+  if (state.barrierSpawnCooldown > 0) {
+    state.barrierSpawnCooldown = static_cast<uint16_t>(state.barrierSpawnCooldown - 1U);
+  }
+
+  for (Barrier &barrier : state.barriers) {
+    if (barrier.phase == BarrierPhase::Inactive) {
+      continue;
+    }
+    if (barrier.framesLeft > 0) {
+      barrier.framesLeft--;
+      continue;
+    }
+    if (barrier.phase == BarrierPhase::Warning) {
+      barrier.phase = BarrierPhase::Active;
+      barrier.framesLeft = BARRIER_ACTIVE_FRAMES;
+    } else {
+      barrier.phase = BarrierPhase::Inactive;
+    }
+  }
+}
+
+void spawn_barriers(GameState &state) {
+  if (!state.hardMode || state.applesEaten < BARRIER_START_APPLES ||
+      state.barrierSpawnCooldown > 0) {
+    return;
+  }
+
+  const int in_use = static_cast<int>(
+      std::count_if(state.barriers.begin(), state.barriers.end(),
+                    [](const Barrier &b) { return b.phase != BarrierPhase::Inactive; }));
+  const int max_allowed = max_concurrent_barriers(state);
+  const int available = max_allowed - in_use;
+  if (available <= 0) {
+    state.barrierSpawnCooldown = BARRIER_RETRY_FRAMES;
+    return;
+  }
+
+  const int max_batch = calculate_barrier_max_batch(state);
+  int to_spawn = 1;
+  if (max_batch > 1 && available > 1) {
+    const int max_possible = std::min(max_batch, available);
+    to_spawn = 1 + (rand() % max_possible);
+  }
+
+  int spawned_count = 0;
+  const int current_max = calculate_barrier_max_length(state);
+  const int length_range = current_max - BARRIER_MIN_LENGTH + 1;
+
+  for (int spawn_idx = 0; spawn_idx < to_spawn; spawn_idx++) {
+    auto free_slot =
+        std::find_if(state.barriers.begin(), state.barriers.end(),
+                     [](const Barrier &b) { return b.phase == BarrierPhase::Inactive; });
+    if (free_slot == state.barriers.end()) {
+      break;
+    }
+
+    bool spawned = false;
+    for (int attempt = 0; attempt < 48; attempt++) {
+      Barrier candidate;
+      candidate.vertical = (rand() % 2) == 0;
+      candidate.length = static_cast<uint8_t>(
+          BARRIER_MIN_LENGTH + (rand() % length_range));
+      // Keep the whole line on screen (barriers never wrap around edges)
+      const int max_x = candidate.vertical ? X_MAX : (X_MAX + 1 - candidate.length);
+      const int max_y = candidate.vertical ? (Y_MAX + 1 - candidate.length) : Y_MAX;
+      candidate.x = static_cast<int8_t>(rand() % (max_x + 1));
+      candidate.y = static_cast<int8_t>(rand() % (max_y + 1));
+
+      bool valid = true;
+      for (int i = 0; i < candidate.length && valid; i++) {
+        const int cx = candidate.x + (candidate.vertical ? 0 : i);
+        const int cy = candidate.y + (candidate.vertical ? i : 0);
+        valid = !cell_blocked_for_barrier(state, cx, cy);
+      }
+
+      if (valid) {
+        candidate.phase = BarrierPhase::Warning;
+        candidate.framesLeft = BARRIER_WARN_FRAMES;
+        *free_slot = candidate;
+        spawned = true;
+        spawned_count++;
+        break;
+      }
+    }
+
+    if (!spawned) {
+      break;
+    }
+  }
+
+  if (spawned_count > 0) {
+    state.barrierSpawnCooldown = static_cast<uint16_t>(
+        calculate_barrier_interval_frames(state) +
+        (rand() % (BARRIER_INTERVAL_JITTER + 1)));
+  } else {
+    state.barrierSpawnCooldown = BARRIER_RETRY_FRAMES;
+  }
+}
+
+bool check_collision_barriers(GameState &state) {
+  if (state.gameOver || state.snake.empty()) {
+    return false;
+  }
+  const auto &head = state.snake.front();
+  if (is_barrier_cell(state, head[0], head[1], false)) {
+    state.gameOver = true;
+    return true;
+  }
+  return false;
+}

source/game_render.cpp

@@ -155,7 +155,8 @@ void draw_apples_cursed(const GameState &state, const RenderAssets &assets,
 void invalidate_hud(RenderAssets &assets) { assets.hudCache.dirty = true; }
 
 void draw_game(const GameState &state, const RenderAssets &assets) {
-  uint16_t oamId = 0;
+  // OAM slots below BARRIER_OAM_SLOTS are owned by draw_barriers() (VBlank)
+  uint16_t oamId = BARRIER_OAM_SLOTS;
 
   if (!state.gameOver) {
     draw_apples(state, assets, oamId);
@@ -180,6 +181,79 @@ void draw_game(const GameState &state, const RenderAssets &assets) {
   iprintf("\x1b[11;12HGAME OVER!");
 }
 
+void draw_barriers(const GameState &state, const RenderAssets &assets,
+                   uint8_t frame) {
+  if (state.scene != Scene::Playing || state.gameOver || !state.hardMode) {
+    oamClear(&oamSub, 0, BARRIER_OAM_SLOTS);
+    return;
+  }
+
+  // Most imminent warning drives the shared warning colour intensity
+  uint16_t min_warn_frames = BARRIER_WARN_FRAMES;
+
+  for (size_t b = 0; b < state.barriers.size(); b++) {
+    const Barrier &barrier = state.barriers.at(b);
+    const int base_slot = static_cast<int>(b) * BARRIER_MAX_LENGTH;
+
+    if (barrier.phase == BarrierPhase::Inactive) {
+      oamClear(&oamSub, base_slot, BARRIER_MAX_LENGTH);
+      continue;
+    }
+
+    const uint16_t frames_left = barrier.framesLeft;
+    bool visible = true;
+    u16 *gfx = assets.gfx_barrier;
+
+    if (barrier.phase == BarrierPhase::Warning) {
+      min_warn_frames = std::min(min_warn_frames, frames_left);
+      if (frames_left < BARRIER_SOLIDIFY_FRAMES) {
+        // About to become solid: rapid flicker between outline and solid look
+        gfx = (((frames_left >> 1U) & 1U) != 0U) ? assets.gfx_barrier
+                                                 : assets.gfx_barrier_warn;
+      } else {
+        // Blink period shrinks from 24 to 4 frames as activation approaches
+        const int elapsed = BARRIER_WARN_FRAMES - frames_left;
+        const int span = BARRIER_WARN_FRAMES - BARRIER_SOLIDIFY_FRAMES;
+        const int period = std::max(4, 24 - ((elapsed * 20) / span));
+        visible = (elapsed % period) < (period / 2);
+        gfx = assets.gfx_barrier_warn;
+      }
+    } else if (frames_left < BARRIER_FADE_FRAMES) {
+      // Still fatal, but slowly blinking to signal it's about to vanish
+      visible = ((frames_left >> 3U) & 1U) == 0U;
+    }
+
+    for (int i = 0; i < BARRIER_MAX_LENGTH; i++) {
+      const int slot = base_slot + i;
+      if (i >= barrier.length) {
+        oamClear(&oamSub, slot, 1);
+        continue;
+      }
+      const int cx = barrier.x + (barrier.vertical ? 0 : i);
+      const int cy = barrier.y + (barrier.vertical ? i : 0);
+      oamSet(&oamSub, slot, cx * 8, cy * 8, 0, 0, SpriteSize_8x8,
+             SpriteColorFormat_256Color, gfx, -1, false, !visible, false, false,
+             false);
+    }
+  }
+
+  // Palette animation (shared by all barriers)
+  const uint8_t pulse = (frame >> 1U) & 7U;
+  const int wave = (pulse < 4U) ? pulse : (7 - pulse); // 0..3..0
+  SPRITE_PALETTE_SUB[BARRIER_PAL_EDGE] = static_cast<uint16_t>(RGB15(12, 0, 3));
+  SPRITE_PALETTE_SUB[BARRIER_PAL_FILL] =
+      static_cast<uint16_t>(RGB15(22 + (wave * 3), 2 + wave, 4));
+  SPRITE_PALETTE_SUB[BARRIER_PAL_STRIPE] =
+      static_cast<uint16_t>(RGB15(31, 22 + (wave * 3), 6 + (wave * 4)));
+
+  // Warning colour ramps from dim orange to hot yellow-white
+  const int urgency =
+      31 - ((static_cast<int>(min_warn_frames) * 31) / BARRIER_WARN_FRAMES);
+  SPRITE_PALETTE_SUB[BARRIER_PAL_WARN] = static_cast<uint16_t>(
+      RGB15(18 + ((urgency * 13) / 31), 4 + ((urgency * 22) / 31),
+            2 + ((urgency * 10) / 31)));
+}
+
 void draw_stats(const GameState &state, RenderAssets &assets, bool internals,
                 bool musicEnabled, uint8_t frame) {
   if (internals) {
@@ -196,7 +270,12 @@ void draw_stats(const GameState &state, RenderAssets &assets, bool internals,
     iprintf("\x1b[7;0HSpeed: %u.%01u Hz (%u%%) ",
             static_cast<unsigned int>(freq_mhz / 1000U),
             static_cast<unsigned int>((freq_mhz % 1000U) / 100U),
-            static_cast<unsigned int>((static_cast<uint32_t>(intensity) * 100U) / 31U));
+            static_cast<unsigned int>(
+                (static_cast<uint32_t>(intensity) * 100U) / 31U));
+    if (state.hardMode) {
+      iprintf("\x1b[8;0HBarriers: max len %u  ",
+              static_cast<unsigned int>(calculate_barrier_max_length(state)));
+    }
   }
 
   HudCache &cache = assets.hudCache;
@@ -274,14 +353,14 @@ void draw_menu(const GameState &state, RenderAssets &assets,
   iprintf("\x1b[3;10HSNAKE PLUS");
   iprintf("\x1b[5;5H---------------------");
 
-  const char *hardModeLabel = state.hardMode ? "ON " : "OFF";
-  const char *musicLabel = musicEnabled ? "ON " : "OFF";
+  const char *hard_mode_label = state.hardMode ? "ON " : "OFF";
+  const char *music_label = musicEnabled ? "ON " : "OFF";
 
   iprintf("\x1b[8;7H%c Start Game", state.menuSelection == 0 ? '>' : ' ');
   iprintf("\x1b[10;7H%c Hard Mode: %s", state.menuSelection == 1 ? '>' : ' ',
-          hardModeLabel);
+          hard_mode_label);
   iprintf("\x1b[12;7H%c Music: %s", state.menuSelection == 2 ? '>' : ' ',
-          musicLabel);
+          music_label);
 
   iprintf("\x1b[19;3HUP/DOWN: Navigate");
   iprintf("\x1b[20;3HA/START: Select");

source/main.cpp

@@ -85,6 +85,8 @@ void setup() {
 	renderAssets.gfx_tail_v[1] = oamAllocateGfx(&oamSub, SpriteSize_8x8, SpriteColorFormat_256Color);
 	renderAssets.gfx_apple_rotten = oamAllocateGfx(&oamSub, SpriteSize_8x8, SpriteColorFormat_256Color);
 	renderAssets.gfx_apple_cursed = oamAllocateGfx(&oamSub, SpriteSize_8x8, SpriteColorFormat_256Color);
+	renderAssets.gfx_barrier = oamAllocateGfx(&oamSub, SpriteSize_8x8, SpriteColorFormat_256Color);
+	renderAssets.gfx_barrier_warn = oamAllocateGfx(&oamSub, SpriteSize_8x8, SpriteColorFormat_256Color);
 
 	dmaCopy(get_sprite_pointer(1), renderAssets.gfx_segment, 64);
 	dmaCopy(get_sprite_pointer(2), renderAssets.gfx_segment_small, 64);
@@ -109,6 +111,12 @@ void setup() {
 	SPRITE_PALETTE_SUB[CURSE_PAL_CORE]    = RGB15(31, 26, 31); // Glowing White-Pink Core
 	SPRITE_PALETTE_SUB[CURSE_PAL_LEAF]    = RGB15(2, 31, 10);  // Toxic Radioactive Neon Green
 
+	// Setup initial colors for the hard-mode temporary fatal barriers
+	SPRITE_PALETTE_SUB[BARRIER_PAL_EDGE]   = RGB15(12, 0, 3);
+	SPRITE_PALETTE_SUB[BARRIER_PAL_FILL]   = RGB15(22, 2, 4);
+	SPRITE_PALETTE_SUB[BARRIER_PAL_STRIPE] = RGB15(31, 22, 6);
+	SPRITE_PALETTE_SUB[BARRIER_PAL_WARN]   = RGB15(18, 4, 2);
+
 	// 8x8 256-color tile data for Cursed Apple (vibrant electric purple apple with radioactive green horn & glowing core)
 	static const uint32_t CURSED_APPLE_TILE[16] = {
 		0x10000000, 0x00001414,
@@ -121,11 +129,47 @@ void setup() {
 		0x10100000, 0x00101000,
 	};
 
+	// 8x8 256-color tile data for solid fatal barrier (bordered hazard stripe block)
+	static const uint32_t BARRIER_SOLID_TILE[16] = {
+		0x15151515, 0x15151515,
+		0x16171715, 0x15171716,
+		0x16161715, 0x15161717,
+		0x17161615, 0x15161617,
+		0x17171615, 0x15171616,
+		0x16171715, 0x15171716,
+		0x16161715, 0x15161717,
+		0x15151515, 0x15151515,
+	};
+
+	// 8x8 256-color tile data for barrier warning announcement (pulsing reticle frame)
+	static const uint32_t BARRIER_WARN_TILE[16] = {
+		0x00001818, 0x18180000,
+		0x18000018, 0x18000018,
+		0x18180000, 0x00001818,
+		0x00181800, 0x00181800,
+		0x00181800, 0x00181800,
+		0x18180000, 0x00001818,
+		0x18000018, 0x18000018,
+		0x00001818, 0x18180000,
+	};
+
 	// Copy cursed apple tile directly into allocated VRAM (32 halfwords)
-	auto *destAppleCursed = static_cast<uint16_t *>(renderAssets.gfx_apple_cursed);
-	const auto *srcAppleCursed = reinterpret_cast<const uint16_t *>(CURSED_APPLE_TILE);
+	auto *dest_apple_cursed = static_cast<uint16_t *>(renderAssets.gfx_apple_cursed);
+	const auto *src_apple_cursed = reinterpret_cast<const uint16_t *>(CURSED_APPLE_TILE);
 	for (size_t i = 0; i < 32; i++) {
-		destAppleCursed[i] = srcAppleCursed[i];
+		dest_apple_cursed[i] = src_apple_cursed[i];
+	}
+
+	auto *dest_barrier = static_cast<uint16_t *>(renderAssets.gfx_barrier);
+	const auto *src_barrier = reinterpret_cast<const uint16_t *>(BARRIER_SOLID_TILE);
+	for (size_t i = 0; i < 32; i++) {
+		dest_barrier[i] = src_barrier[i];
+	}
+
+	auto *dest_barrier_warn = static_cast<uint16_t *>(renderAssets.gfx_barrier_warn);
+	const auto *src_barrier_warn = reinterpret_cast<const uint16_t *>(BARRIER_WARN_TILE);
+	for (size_t i = 0; i < 32; i++) {
+		dest_barrier_warn[i] = src_barrier_warn[i];
 	}
 
 	audio_setup(audioContext);
@@ -137,6 +181,10 @@ void handle_vblank() {
 	if (gameState.scene == Scene::Playing) {
 		consoleSelect(&topScreen);
 		draw_stats(gameState, renderAssets, internals, audio_is_music_enabled(audioContext), frame);
+		if (!gameState.paused) {
+			tick_barriers_frame(gameState);
+		}
+		draw_barriers(gameState, renderAssets, frame);
 	}
 
 	// Dynamic pulsing radioactive glow for Cursed Apples (smooth 60fps breathing)
@@ -157,7 +205,7 @@ void do_tick() {
 	if (gameState.scene == Scene::Playing && !paused) {
 		ticks++;
 		if (!gameOver){
-			const bool wasGameOver = gameOver;
+			const bool was_game_over = gameOver;
 			
 			/*if (hardMode) {
 				timerStop(0);
@@ -167,6 +215,9 @@ void do_tick() {
 			update_snake(gameState);
 			audio_play_plop(audioContext);
 			check_collision_self(gameState);
+			if (check_collision_barriers(gameState)) {
+				audio_play_boom(audioContext);
+			}
 			if (check_collision_apples(gameState)) {
 				audio_play_pickup(audioContext);
 				bg_trigger_pulse(bgContext);
@@ -181,8 +232,9 @@ void do_tick() {
 			spawn_apples(gameState);
 			spawn_apples_rotten(gameState);
 			spawn_apples_cursed(gameState);
+			spawn_barriers(gameState);
 			tick_status_effects(gameState);
-			if (!wasGameOver && gameOver) {
+			if (!was_game_over && gameOver) {
 				audio_stop_music();
 				audio_play_fail(audioContext);
 			}
@@ -194,6 +246,7 @@ void do_tick() {
 	
 void init_game() {
 	applesEaten = 0;
+	reset_barriers(gameState);
 	if (hardMode) {
 		timerStart(0, ClockDivider_1024, calculate_timer_reload(gameState), do_tick);
 		setBackdropColorSub(RGB15(8, 3, 3));