gameboy-hello-iso/engine.c

#include <gb/gb.h>
#include <stdint.h>
#include <string.h>
#include <rand.h>
#include "engine.h"

// Generated by png2asset
#include "tiles.h"
#include "player.h"

#define MAP_SIZE 7

uint8_t maze[MAP_SIZE][MAP_SIZE];
static uint8_t map_buffer[32 * 32];

uint8_t player_lx = 1;
uint8_t player_ly = 1;
uint8_t player_dir = 0; // 0=DR, 1=DL, 2=UL, 3=UR
uint8_t walk_timer = 0;
uint8_t scroll_x = 0;
uint8_t scroll_y = 0;

// DAS variables
uint8_t das_timer = 0;
uint8_t das_active = 0;
#define DAS_DELAY 12
#define DAS_REPEAT 6

static void generate_maze(void) {
    // Clear maze (all 0/walls)
    memset(maze, 0, sizeof(maze));
    
    // Stack for backtracking (3x3 grid has 9 odd cells max)
    uint8_t stack_x[9];
    uint8_t stack_y[9];
    uint8_t stack_ptr = 0;
    
    // Start at (1, 1)
    uint8_t cx = 1;
    uint8_t cy = 1;
    maze[cy][cx] = 1;
    
    while (1) {
        // Find unvisited neighbors at distance 2
        // Up: (cx, cy-2), Down: (cx, cy+2), Left: (cx-2, cy), Right: (cx+2, cy)
        uint8_t nx[4];
        uint8_t ny[4];
        uint8_t count = 0;
        
        // Up
        if (cy >= 3 && maze[cy - 2][cx] == 0) {
            nx[count] = cx; ny[count] = cy - 2; count++;
        }
        // Down
        if (cy <= 3 && maze[cy + 2][cx] == 0) {
            nx[count] = cx; ny[count] = cy + 2; count++;
        }
        // Left
        if (cx >= 3 && maze[cy][cx - 2] == 0) {
            nx[count] = cx - 2; ny[count] = cy; count++;
        }
        // Right
        if (cx <= 3 && maze[cy][cx + 2] == 0) {
            nx[count] = cx + 2; ny[count] = cy; count++;
        }
        
        if (count > 0) {
            // Choose a random neighbor
            uint8_t dir = rand() % count;
            
            // Push current cell to stack
            stack_x[stack_ptr] = cx;
            stack_y[stack_ptr] = cy;
            stack_ptr++;
            
            // Remove wall between current cell and chosen neighbor
            maze[(cy + ny[dir]) / 2][(cx + nx[dir]) / 2] = 1;
            
            // Move to neighbor
            cx = nx[dir];
            cy = ny[dir];
            maze[cy][cx] = 1;
        } else if (stack_ptr > 0) {
            // Pop from stack
            stack_ptr--;
            cx = stack_x[stack_ptr];
            cy = stack_y[stack_ptr];
        } else {
            break;
        }
    }
}

static void draw_map(void) {
    // Fill entire map with tile index 0 (completely black empty tile)
    memset(map_buffer, 0, sizeof(map_buffer));
    
    // Draw logical map path tiles
    for (int8_t ly = 0; ly < MAP_SIZE; ly++) {
        for (int8_t lx = 0; lx < MAP_SIZE; lx++) {
            if (maze[ly][lx] == 1) {
                // Centering math for 7x7 map on 32x32 background map
                int8_t iso_x = (lx - ly) * 2 + 12; 
                int8_t iso_y = (lx + ly) * 1 + 2;  

                // Alternate colors (checkerboard)
                uint8_t is_alt = ((lx + ly) % 2 == 0);
                
                // Calculate neighbor mask
                uint8_t has_tl = (lx > 0 && maze[ly][lx - 1] == 1);
                uint8_t has_tr = (ly > 0 && maze[ly - 1][lx] == 1);
                uint8_t has_bl = (ly < MAP_SIZE - 1 && maze[ly + 1][lx] == 1);
                uint8_t has_br = (lx < MAP_SIZE - 1 && maze[ly][lx + 1] == 1);
                
                uint8_t mask = (has_tl ? 1 : 0) | (has_tr ? 2 : 0) | (has_bl ? 4 : 0) | (has_br ? 8 : 0);
                uint8_t v = is_alt ? (16 + mask) : mask;

                for (uint8_t y = 0; y < 2; y++) {
                    for (uint8_t x = 0; x < 4; x++) {
                        uint8_t target_x = (iso_x + x) & 31;
                        uint8_t target_y = (iso_y + y) & 31;
                        
                        uint8_t src_tile = tiles_map[4 + v * 8 + y * 4 + x];
                        map_buffer[target_y * 32 + target_x] = src_tile;
                    }
                }
            }
        }
    }
    
    set_bkg_tiles(0, 0, 32, 32, map_buffer);
}

static void update_camera(void) {
    // Center the camera on the player's logical tile coordinates
    int16_t px = (player_lx - player_ly) * 16 + 96; 
    int16_t py = (player_lx + player_ly) * 8 + 16;   
    
    scroll_x = px - 64;
    scroll_y = py - 72;
    
    move_bkg(scroll_x, scroll_y);
}

static void update_player_sprite(void) {
    uint8_t frame_offset = (walk_timer > 0) ? ((walk_timer >> 2) & 1) : 0;
    move_metasprite(player_metasprites[player_dir * 2 + frame_offset], 0, 0, 88, 88);
}

void engine_init(void) {
    SPRITES_8x16;
    
    // Seed random number generator with hardware divider register
    initrand(DIV_REG);
    
    // Generate maze path cells
    generate_maze();
    
    // Explicitly initialize DMG palette registers
    OBP0_REG = 0xE4; // 11 10 01 00 (Black, Dark Gray, Light Gray, White)
    BGP_REG = 0xE4;
    
    // Initialize GBC palettes (safe on DMG, does nothing)
    set_bkg_palette(0, 8, tiles_palettes);
    set_sprite_palette(0, 8, player_palettes);
    
    // Load tiles
    set_bkg_data(0, tiles_TILE_COUNT, tiles_tiles);
    set_sprite_data(0, player_TILE_COUNT, player_tiles);

    draw_map();
    update_camera();
    update_player_sprite();
}

void engine_update(uint8_t keys, uint8_t prev_keys) {
    if (walk_timer > 0) {
        walk_timer--;
        update_player_sprite();
    }

    uint8_t keys_pressed = keys & ~prev_keys;

    int8_t move_lx = 0;
    int8_t move_ly = 0;

    if (keys_pressed) {
        das_timer = DAS_DELAY;
        das_active = 1;
    } else if (keys && das_active) {
        das_timer--;
        if (das_timer == 0) {
            das_timer = DAS_REPEAT;
            keys_pressed = keys; // trigger move
        }
    } else {
        das_active = 0;
    }

    if (keys_pressed & J_RIGHT) {
        move_lx = 1; player_dir = 0; // DR
    } else if (keys_pressed & J_LEFT) {
        move_lx = -1; player_dir = 2; // UL
    } else if (keys_pressed & J_DOWN) {
        move_ly = 1; player_dir = 1; // DL
    } else if (keys_pressed & J_UP) {
        move_ly = -1; player_dir = 3; // UR
    }

    if (move_lx != 0 || move_ly != 0) {
        int8_t new_lx = player_lx + move_lx;
        int8_t new_ly = player_ly + move_ly;

        // Bounds check & wall/empty area collision check
        if (new_lx >= 0 && new_lx < MAP_SIZE && new_ly >= 0 && new_ly < MAP_SIZE) {
            if (maze[new_ly][new_lx] == 1) {
                player_lx = new_lx;
                player_ly = new_ly;
                walk_timer = 12; // 12 frames of walk cycle
            }
        }
        update_player_sprite();
        update_camera();
    }
}