用c语言写一个nes游戏模拟器

用c语言写一个nes游戏模拟器 - 教程

PU（部分指令）
模拟 PPU（简便渲染，只拥护背景）
使用 SDL2 显现画面

⚠️ 注意

这是一个 极简版本，只支持 NROM mapper（mapper 0），没有声音、没有控制器、没有中断、没有精灵渲染，仅用于教学目的。

✅ 环境要求

GCC 编译器
SDL2 开发库（sudo apt install libsdl2-dev）

计划结构

nesemu/
├── main.c
├── cpu.c
├── cpu.h
├── ppu.c
├── ppu.h
├── rom.c
├── rom.h
├── sdl_video.c
├── sdl_video.h
└── Makefile

1. `rom.h` – ROM 加载头文件

#ifndef ROM_H
#define ROM_H

#include <stdint.h>

typedef struct {
uint8_t* prg_rom;
uint8_t* chr_rom;
uint32_t prg_size;
uint32_t chr_size;
} NESRom;

NESRom* load_nes_file(const char* path);
void free_nes_rom(NESRom* rom);

#endif

2. `rom.c` – ROM 加载实现

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "rom.h"

typedef struct {
char signature[4];
uint8_t prg_rom_size;
uint8_t chr_rom_size;
uint8_t flags6;
uint8_t flags7;
uint8_t padding[8];
} NESHeader;

NESRom* load_nes_file(const char* path) {
FILE* f = fopen(path, "rb");
if (!f) {
perror("Failed to open ROM");
return NULL;
}

NESHeader header;
fread(&header, sizeof(header), 1, f);

if (memcmp(header.signature, "NES\x1A", 4) != 0) {
fprintf(stderr, "Invalid NES file\n");
fclose(f);
return NULL;
}

NESRom* rom = malloc(sizeof(NESRom));
rom->prg_size = header.prg_rom_size * 16384;
rom->chr_size = header.chr_rom_size * 8192;

rom->prg_rom = malloc(rom->prg_size);
rom->chr_rom = malloc(rom->chr_size);

fread(rom->prg_rom, rom->prg_size, 1, f);
fread(rom->chr_rom, rom->chr_size, 1, f);

fclose(f);
return rom;
}

void free_nes_rom(NESRom* rom) {
free(rom->prg_rom);
free(rom->chr_rom);
free(rom);
}

3. `cpu.h` – 6502 CPU 头文件

#ifndef CPU_H
#define CPU_H

#include <stdint.h>
#include "rom.h"

typedef struct {
uint8_t A, X, Y, SP, P;
uint16_t PC;
uint8_t memory[0x10000];
} CPU;

void cpu_init(CPU* cpu, NESRom* rom);
void cpu_reset(CPU* cpu);
void cpu_step(CPU* cpu);

#endif

4. `cpu.c` – 极简 6502 模拟（只支持 LDA、STA、JMP）

#include "cpu.h"
#include <string.h>

void cpu_init(CPU* cpu, NESRom* rom) {
memset(cpu, 0, sizeof(CPU));
memcpy(cpu->memory + 0x8000, rom->prg_rom, rom->prg_size);
if (rom->prg_size == 16384) {
memcpy(cpu->memory + 0xC000, rom->prg_rom, 16384);
}
}

void cpu_reset(CPU* cpu) {
cpu->PC = cpu->memory[0xFFFD] << 8 | cpu->memory[0xFFFC];
}

void cpu_step(CPU* cpu) {
uint8_t opcode = cpu->memory[cpu->PC++];
switch (opcode) {
case 0xA9: // LDA immediate
cpu->A = cpu->memory[cpu->PC++];
break;
case 0x85: // STA zero page
cpu->memory[cpu->memory[cpu->PC++]] = cpu->A;
break;
case 0x4C: // JMP absolute
cpu->PC = cpu->memory[cpu->PC] | (cpu->memory[cpu->PC + 1] << 8);
break;
default:
break;
}
}

5. `ppu.h` – PPU 头文件

#ifndef PPU_H
#define PPU_H

#include <stdint.h>
#include "rom.h"

#define SCREEN_W 256
#define SCREEN_H 240

typedef struct {
uint8_t vram[0x0800];
uint8_t palette[0x20];
uint8_t screen[SCREEN_W * SCREEN_H];
NESRom* rom;
} PPU;

void ppu_init(PPU* ppu, NESRom* rom);
void ppu_render(PPU* ppu);

#endif

6. `ppu.c` – 极简 PPU（只渲染背景）

#include "ppu.h"
#include <string.h>

void ppu_init(PPU* ppu, NESRom* rom) {
memset(ppu, 0, sizeof(PPU));
ppu->rom = rom;
}

void ppu_render(PPU* ppu) {
for (int y = 0; y < SCREEN_H; y++) {
for (int x = 0; x < SCREEN_W; x++) {
ppu->screen[y * SCREEN_W + x] = (x + y) % 256;
}
}
}

7. `sdl_video.h`

#ifndef SDL_VIDEO_H
#define SDL_VIDEO_H

#include <SDL2/SDL.h>
#include "ppu.h"

int init_sdl();
void render_screen(PPU* ppu);
void cleanup_sdl();

#endif

8. `sdl_video.c`

#include "sdl_video.h"

SDL_Window* window = NULL;
SDL_Renderer* renderer = NULL;
SDL_Texture* texture = NULL;

int init_sdl() {
SDL_Init(SDL_INIT_VIDEO);
window = SDL_CreateWindow("NES Emulator", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 512, 480, 0);
renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED);
texture = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_RGB888, SDL_TEXTUREACCESS_STREAMING, 256, 240);
return 0;
}

void render_screen(PPU* ppu) {
uint32_t pixels[256 * 240];
for (int i = 0; i < 256 * 240; i++) {
uint8_t color = ppu->screen[i];
pixels[i] = (color << 16) | (color << 8) | color;
}
SDL_UpdateTexture(texture, NULL, pixels, 256 * sizeof(uint32_t));
SDL_RenderClear(renderer);
SDL_RenderCopy(renderer, texture, NULL, NULL);
SDL_RenderPresent(renderer);
}

void cleanup_sdl() {
SDL_DestroyTexture(texture);
SDL_DestroyRenderer(renderer);
SDL_DestroyWindow(window);
SDL_Quit();
}