feat: prevent reversing directly into snake neck and play denied sound effect

AGENTS.md

@@ -37,7 +37,7 @@ snakePlus/
 ├── source/                     # C++ Implementation files
 │   ├── main.cpp                # Hardware setup, VBlank IRQ, timer ticks, game bootstrap
 │   ├── game_audio.cpp          # MaxMod soundbank loading, BGM loop, SFX dispatch
-│   ├── game_input.cpp          # Key mapping, inverted control logic, menu navigation
+│   ├── game_input.cpp          # Key mapping, inverted control logic, reverse-denial, menu navigation
 │   ├── game_logic.cpp          # Position update, edge wrapping, collision resolution, RNG
 │   └── game_render.cpp         # OAM sprite rendering, console text HUD & menu screens
 │
@@ -51,6 +51,7 @@ snakePlus/
 │   ├── 273792__pacomav__plop.wav                                  # Movement plop SFX
 │   ├── 332629__treasuresounds__item-pickup.wav                    # Apple pickup SFX
 │   ├── Boom.wav                                                   # Rotten / Cursed apple boom SFX
+│   ├── denied.wav                                                  # Reverse-direction denied thud SFX (synthesized)
 │   ├── 167126__crisstanza__unpause.wav                            # Unpause SFX
 │   ├── 167127__crisstanza__pause.wav                              # Pause SFX
 │   └── 73750__timbre__remix-of-benboncan-sad-trombone-more-wah-bright-de-clicked.wav # Fail SFX
@@ -95,6 +96,7 @@ The game operates in one of two scenes ([`Scene`](include/game_state.h#L9-L12)):
 - **Normal Apple (Red):** Spawns if count < 1. Awards +10 score, increases length by 1, plays pickup sound. Flashes/blinks every 4 ticks.
 - **Rotten Apple (Brown/Green):** Spawns in Hard Mode (periodic chance up to 20 on screen). Decreases length by 1, plays explosion SFX. If length drops below 2, triggers Game Over.
 - **Cursed Apple (Purple):** Spawns occasionally. Inverts player steering controls (Up ↔ Down, Left ↔ Right) for `CURSE_DURATION_TICKS` (40 ticks). The sprite is procedurally constructed at startup in [`main.cpp:91-112`](source/main.cpp#L91-L112) by copying the rotten apple tile pixels and mapping them to dedicated palette entries (`CURSE_PAL_SHADOW`, `CURSE_PAL_OUTLINE`, `CURSE_PAL_FILL`, `CURSE_PAL_GLOW`).
+- **Reverse-Direction Denial:** Pressing the D-Pad in the exact opposite direction (i.e. into the snake's own neck) is silently denied instead of causing an immediate Game Over. The game computes the would-be next head position (including edge-wrapping) and compares it to the neck segment; if they match, the direction change is rejected and a subtle "denied" thud SFX plays.
 
 ### 3.4 Game Modes
 - **Normal Mode:** Starts with length 4, timer frequency `TIMER_FREQ_1024(5)`, background color `RGB15(5,5,5)`.
@@ -108,7 +110,7 @@ The game operates in one of two scenes ([`Scene`](include/game_state.h#L9-L12)):
 |---|---|---|
 | **Menu** | D-Pad Up / Down | Change selected menu item |
 | **Menu** | A / START | Select / Toggle option / Start game |
-| **Playing** | D-Pad | Steer snake (inverted if cursed) |
+| **Playing** | D-Pad | Steer snake (inverted if cursed; reversing into neck is denied with subtle SFX) |
 | **Playing** | START | Pause / Unpause |
 | **Playing** | R | Swap LCD displays (`lcdSwap()`) |
 | **Playing** | SELECT | Toggle debug internals HUD overlay |

CMakeLists.txt

@@ -40,12 +40,12 @@ if(ENABLE_CLANG_TIDY)
 
         set(CMAKE_C_CLANG_TIDY
                 ${CLANG_TIDY_EXE}
-                --header-filter=^(include|source)/
+                "--header-filter=^(include|source)/"
                 --extra-arg=--target=arm-none-eabi
         )
         set(CMAKE_CXX_CLANG_TIDY
                 ${CLANG_TIDY_EXE}
-                --header-filter=^(include|source)/
+                "--header-filter=^(include|source)/"
                 --extra-arg=--target=arm-none-eabi
         )
 endif()

include/game_audio.h

@@ -12,6 +12,7 @@ struct AudioContext {
     mm_sound_effect sfx_unpause;
     mm_sound_effect sfx_plop;
     mm_sound_effect sfx_fail;
+    mm_sound_effect sfx_denied;
 };
 
 void audio_setup(AudioContext &audio);
@@ -26,6 +27,7 @@ void audio_play_plop(const AudioContext &audio);
 void audio_play_pause(const AudioContext &audio);
 void audio_play_unpause(const AudioContext &audio);
 void audio_play_fail(const AudioContext &audio);
+void audio_play_denied(const AudioContext &audio);
 
 bool audio_toggle_music(AudioContext &audio);
 bool audio_is_music_enabled(const AudioContext &audio);

source/game_audio.cpp

@@ -14,6 +14,7 @@ void audio_setup(AudioContext &audio) {
     mmLoadEffect(SFX_167126__CRISSTANZA__UNPAUSE);
     mmLoadEffect(SFX_273792__PACOMAV__PLOP);
     mmLoadEffect(SFX_73750__TIMBRE__REMIX_OF_BENBONCAN_SAD_TROMBONE_MORE_WAH_BRIGHT_DE_CLICKED);
+    mmLoadEffect(SFX_DENIED);
 
     audio.sfx_pickup = {
         { SFX_332629__TREASURESOUNDS__ITEM_PICKUP },
@@ -62,6 +63,14 @@ void audio_setup(AudioContext &audio) {
         255,
         128,
     };
+
+    audio.sfx_denied = {
+        { SFX_DENIED },
+        static_cast<int>(1.0F * (1 << 10)),
+        5,
+        160,
+        128,
+    };
 }
 
 void audio_start_music(const AudioContext &audio) {
@@ -111,6 +120,10 @@ void audio_play_fail(const AudioContext &audio) {
     mmEffectEx(&audio.sfx_fail);
 }
 
+void audio_play_denied(const AudioContext &audio) {
+    mmEffectEx(&audio.sfx_denied);
+}
+
 bool audio_toggle_music(AudioContext &audio) {
     audio.musicEnabled = !audio.musicEnabled;
 

source/game_input.cpp

@@ -4,6 +4,8 @@
 #include <cstdint>
 #include <cstdio>
 
+#include "consts.h"
+
 bool handle_input_frame(InputContext &ctx) {
     scanKeys();
     const uint32_t keys = keysDown();
@@ -69,27 +71,78 @@ bool handle_input_frame(InputContext &ctx) {
 
     if (!ctx.state->paused && !ctx.state->gameOver) {
         const bool cursed = ctx.state->curseTicksRemaining > 0;
+        uint16_t requested_dir = 0;
+        bool has_dir_input = false;
 
         if ((keys != 0U) && ((keys & KEY_UP) != 0U)) {
-            ctx.state->snakeDirection = cursed ? 2 : 0;
-            draw_game(*ctx.state, *ctx.renderAssets);
+            requested_dir = cursed ? 2 : 0;
+            has_dir_input = true;
+        } else if ((keys != 0U) && ((keys & KEY_RIGHT) != 0U)) {
+            requested_dir = cursed ? 3 : 1;
+            has_dir_input = true;
+        } else if ((keys != 0U) && ((keys & KEY_DOWN) != 0U)) {
+            requested_dir = cursed ? 0 : 2;
+            has_dir_input = true;
+        } else if ((keys != 0U) && ((keys & KEY_LEFT) != 0U)) {
+            requested_dir = cursed ? 1 : 3;
+            has_dir_input = true;
         }
 
-        if ((keys != 0U) && ((keys & KEY_RIGHT) != 0U)) {
-            ctx.state->snakeDirection = cursed ? 3 : 1;
-            draw_game(*ctx.state, *ctx.renderAssets);
+        if (has_dir_input) {
+            bool is_reversing = false;
+
+            if (ctx.state->snake.size() >= 2) {
+                const auto &head = ctx.state->snake.front();
+                const auto &neck = ctx.state->snake.at(1);
+                int next_x = head[0];
+                int next_y = head[1];
+
+                switch (requested_dir) {
+                case 0:
+                    next_y--;
+                    break;
+                case 1:
+                    next_x++;
+                    break;
+                case 2:
+                    next_y++;
+                    break;
+                case 3:
+                    next_x--;
+                    break;
+                default:
+                    break;
                 }
 
-        if ((keys != 0U) && ((keys & KEY_DOWN) != 0U)) {
-            ctx.state->snakeDirection = cursed ? 0 : 2;
-            draw_game(*ctx.state, *ctx.renderAssets);
+                if (next_x > X_MAX) {
+                    next_x = 0;
+                } else if (next_x < 0) {
+                    next_x = X_MAX;
                 }
 
-        if ((keys != 0U) && ((keys & KEY_LEFT) != 0U)) {
-            ctx.state->snakeDirection = cursed ? 1 : 3;
+                if (next_y > Y_MAX) {
+                    next_y = 0;
+                } else if (next_y < 0) {
+                    next_y = Y_MAX;
+                }
+
+                if (next_x == neck[0] && next_y == neck[1]) {
+                    is_reversing = true;
+                }
+            } else {
+                if ((ctx.state->snakeDirection + 2) % 4 == requested_dir) {
+                    is_reversing = true;
+                }
+            }
+
+            if (is_reversing) {
+                audio_play_denied(*ctx.audio);
+            } else if (ctx.state->snakeDirection != requested_dir) {
+                ctx.state->snakeDirection = requested_dir;
                 draw_game(*ctx.state, *ctx.renderAssets);
             }
         }
+    }
 
     if (ctx.state->paused) {
         if ((keys != 0U) && ((keys & KEY_X) != 0U)) {

source/main.cpp

@@ -175,7 +175,7 @@ void do_tick() {
 void init_game() {
 	
 	if (hardMode) {
-		timerStart(0, ClockDivider_1024, TIMER_FREQ_1024(9), do_tick);
+		timerStart(0, ClockDivider_1024, static_cast<uint16_t>(TIMER_FREQ_1024(9)), do_tick);
 		setBackdropColorSub(RGB15(10,5,5));
 		score = 0;
 		snakelength = START_LENGTH_HARD;
@@ -197,7 +197,7 @@ void init_game() {
 	} 
 	else
 	{
-		timerStart(0, ClockDivider_1024, TIMER_FREQ_1024(5), do_tick);
+		timerStart(0, ClockDivider_1024, static_cast<uint16_t>(TIMER_FREQ_1024(5)), do_tick);
 		setBackdropColorSub(RGB15(5,5,5));
 		score = 0;
 		snakelength = START_LENGTH;