Initial commit of isometric Game Boy adventure prototype
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#include <gb/gb.h>
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#include <stdint.h>
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#include <string.h>
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#include <rand.h>
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#include "engine.h"
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// Generated by png2asset
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#include "tiles.h"
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#include "player.h"
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#define MAP_SIZE 7
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uint8_t maze[MAP_SIZE][MAP_SIZE];
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static uint8_t map_buffer[32 * 32];
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uint8_t player_lx = 1;
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uint8_t player_ly = 1;
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uint8_t player_dir = 0; // 0=DR, 1=DL, 2=UL, 3=UR
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uint8_t walk_timer = 0;
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uint8_t scroll_x = 0;
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uint8_t scroll_y = 0;
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// DAS variables
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uint8_t das_timer = 0;
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uint8_t das_active = 0;
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#define DAS_DELAY 12
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#define DAS_REPEAT 6
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static void generate_maze(void) {
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// Clear maze (all 0/walls)
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memset(maze, 0, sizeof(maze));
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// Stack for backtracking (3x3 grid has 9 odd cells max)
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uint8_t stack_x[9];
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uint8_t stack_y[9];
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uint8_t stack_ptr = 0;
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// Start at (1, 1)
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uint8_t cx = 1;
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uint8_t cy = 1;
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maze[cy][cx] = 1;
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while (1) {
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// Find unvisited neighbors at distance 2
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// Up: (cx, cy-2), Down: (cx, cy+2), Left: (cx-2, cy), Right: (cx+2, cy)
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uint8_t nx[4];
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uint8_t ny[4];
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uint8_t count = 0;
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// Up
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if (cy >= 3 && maze[cy - 2][cx] == 0) {
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nx[count] = cx; ny[count] = cy - 2; count++;
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}
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// Down
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if (cy <= 3 && maze[cy + 2][cx] == 0) {
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nx[count] = cx; ny[count] = cy + 2; count++;
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}
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// Left
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if (cx >= 3 && maze[cy][cx - 2] == 0) {
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nx[count] = cx - 2; ny[count] = cy; count++;
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}
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// Right
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if (cx <= 3 && maze[cy][cx + 2] == 0) {
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nx[count] = cx + 2; ny[count] = cy; count++;
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}
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if (count > 0) {
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// Choose a random neighbor
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uint8_t dir = rand() % count;
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// Push current cell to stack
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stack_x[stack_ptr] = cx;
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stack_y[stack_ptr] = cy;
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stack_ptr++;
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// Remove wall between current cell and chosen neighbor
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maze[(cy + ny[dir]) / 2][(cx + nx[dir]) / 2] = 1;
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// Move to neighbor
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cx = nx[dir];
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cy = ny[dir];
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maze[cy][cx] = 1;
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} else if (stack_ptr > 0) {
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// Pop from stack
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stack_ptr--;
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cx = stack_x[stack_ptr];
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cy = stack_y[stack_ptr];
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} else {
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break;
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}
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}
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}
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static void draw_map(void) {
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// Fill entire map with tile index 0 (completely black empty tile)
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memset(map_buffer, 0, sizeof(map_buffer));
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// Draw logical map path tiles
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for (int8_t ly = 0; ly < MAP_SIZE; ly++) {
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for (int8_t lx = 0; lx < MAP_SIZE; lx++) {
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if (maze[ly][lx] == 1) {
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// Centering math for 7x7 map on 32x32 background map
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int8_t iso_x = (lx - ly) * 2 + 12;
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int8_t iso_y = (lx + ly) * 1 + 2;
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// Alternate colors (checkerboard)
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uint8_t is_alt = ((lx + ly) % 2 == 0);
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// Calculate neighbor mask
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uint8_t has_tl = (lx > 0 && maze[ly][lx - 1] == 1);
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uint8_t has_tr = (ly > 0 && maze[ly - 1][lx] == 1);
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uint8_t has_bl = (ly < MAP_SIZE - 1 && maze[ly + 1][lx] == 1);
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uint8_t has_br = (lx < MAP_SIZE - 1 && maze[ly][lx + 1] == 1);
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uint8_t mask = (has_tl ? 1 : 0) | (has_tr ? 2 : 0) | (has_bl ? 4 : 0) | (has_br ? 8 : 0);
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uint8_t v = is_alt ? (16 + mask) : mask;
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for (uint8_t y = 0; y < 2; y++) {
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for (uint8_t x = 0; x < 4; x++) {
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uint8_t target_x = (iso_x + x) & 31;
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uint8_t target_y = (iso_y + y) & 31;
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uint8_t src_tile = tiles_map[4 + v * 8 + y * 4 + x];
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map_buffer[target_y * 32 + target_x] = src_tile;
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}
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}
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}
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}
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}
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set_bkg_tiles(0, 0, 32, 32, map_buffer);
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}
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static void update_camera(void) {
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// Center the camera on the player's logical tile coordinates
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int16_t px = (player_lx - player_ly) * 16 + 96;
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int16_t py = (player_lx + player_ly) * 8 + 16;
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scroll_x = px - 64;
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scroll_y = py - 72;
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move_bkg(scroll_x, scroll_y);
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}
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static void update_player_sprite(void) {
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uint8_t frame_offset = (walk_timer > 0) ? ((walk_timer >> 2) & 1) : 0;
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move_metasprite(player_metasprites[player_dir * 2 + frame_offset], 0, 0, 88, 88);
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}
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void engine_init(void) {
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SPRITES_8x16;
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// Seed random number generator with hardware divider register
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initrand(DIV_REG);
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// Generate maze path cells
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generate_maze();
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// Explicitly initialize DMG palette registers
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OBP0_REG = 0xE4; // 11 10 01 00 (Black, Dark Gray, Light Gray, White)
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BGP_REG = 0xE4;
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// Initialize GBC palettes (safe on DMG, does nothing)
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set_bkg_palette(0, 8, tiles_palettes);
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set_sprite_palette(0, 8, player_palettes);
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// Load tiles
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set_bkg_data(0, tiles_TILE_COUNT, tiles_tiles);
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set_sprite_data(0, player_TILE_COUNT, player_tiles);
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draw_map();
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update_camera();
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update_player_sprite();
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}
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void engine_update(uint8_t keys, uint8_t prev_keys) {
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if (walk_timer > 0) {
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walk_timer--;
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update_player_sprite();
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}
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uint8_t keys_pressed = keys & ~prev_keys;
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int8_t move_lx = 0;
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int8_t move_ly = 0;
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if (keys_pressed) {
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das_timer = DAS_DELAY;
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das_active = 1;
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} else if (keys && das_active) {
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das_timer--;
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if (das_timer == 0) {
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das_timer = DAS_REPEAT;
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keys_pressed = keys; // trigger move
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}
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} else {
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das_active = 0;
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}
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if (keys_pressed & J_RIGHT) {
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move_lx = 1; player_dir = 0; // DR
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} else if (keys_pressed & J_LEFT) {
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move_lx = -1; player_dir = 2; // UL
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} else if (keys_pressed & J_DOWN) {
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move_ly = 1; player_dir = 1; // DL
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} else if (keys_pressed & J_UP) {
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move_ly = -1; player_dir = 3; // UR
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}
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if (move_lx != 0 || move_ly != 0) {
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int8_t new_lx = player_lx + move_lx;
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int8_t new_ly = player_ly + move_ly;
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// Bounds check & wall/empty area collision check
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if (new_lx >= 0 && new_lx < MAP_SIZE && new_ly >= 0 && new_ly < MAP_SIZE) {
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if (maze[new_ly][new_lx] == 1) {
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player_lx = new_lx;
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player_ly = new_ly;
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walk_timer = 12; // 12 frames of walk cycle
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}
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}
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update_player_sprite();
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update_camera();
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}
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}
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