c++-PPSSPP：跨平台PSP模拟器的C++开发实践

icy 昨天 11 抢沙发

默认

摘要： PPSSPP：跨平台PSP模拟器的C++开发实践项目概述 PPSSPP（PlayStation Portable Simulator Suitable for Playing P...

PPSSPP：跨平台PSP模拟器的C++开发实践

项目概述

PPSSPP（PlayStation Portable Simulator Suitable for Playing Portably）是一个开源的PlayStation Portable（PSP）游戏模拟器，由Henrik Rydgård（hrydgard）主导开发。该项目采用C++编写，支持Windows、macOS、Linux、Android、iOS等多个平台，实现了对PSP游戏的高性能模拟。

核心技术架构

1. 多平台抽象层

PPSSPP使用自定义的跨平台抽象层，封装了不同操作系统的系统调用：

text

// 示例：文件系统抽象接口
class File {
public:
    virtual ~File() {}
    virtual size_t Read(void *buffer, size_t bytes) = 0;
    virtual size_t Write(const void *buffer, size_t bytes) = 0;
    virtual void Seek(s64 offset, int whence) = 0;
    virtual size_t GetSize() = 0;
    virtual bool IsOpen() const = 0;
    
    static File *Open(const std::string &filename, const char *mode);
};

2. PSP硬件模拟

项目实现了完整的PSP硬件模拟栈：

text

// CPU模拟核心（基于MIPS架构）
class MIPSState {
public:
    void RunLoop();
    void ExecuteInstruction(MIPSOpcode opcode);
    
    // 寄存器状态
    u32 reg[32];
    u32 pc;
    u32 hi, lo;
    
private:
    void InterpretInstruction(MIPSOpcode opcode);
    void CompileBlock(u32 startAddress);
};

3. 图形渲染系统

PPSSPP支持多种图形后端，包括OpenGL、Vulkan和DirectX：

text

// 图形上下文抽象
class DrawContext {
public:
    virtual void Init() = 0;
    virtual void Shutdown() = 0;
    
    virtual void BeginFrame() = 0;
    virtual void EndFrame() = 0;
    
    virtual void BindTexture(int unit, Texture *texture) = 0;
    virtual void DrawElements(Primitive prim, int count) = 0;
    
    static DrawContext *Create(GraphicsAPI api);
};

// Vulkan实现示例
class VulkanContext : public DrawContext {
public:
    void Init() override {
        // 初始化Vulkan实例、设备、交换链等
        CreateInstance();
        SetupDebugCallback();
        PickPhysicalDevice();
        CreateLogicalDevice();
        CreateSwapChain();
    }
    
private:
    VkInstance instance_;
    VkDevice device_;
    VkSwapchainKHR swapChain_;
};

关键特性实现

1. JIT编译器优化

PPSSPP包含一个高效的动态重编译器（Dynarec），将MIPS指令转换为本地代码：

text

class MIPSJit {
public:
    void CompileBlock(u32 startAddress) {
        const u32 *code = GetCodePointer(startAddress);
        u32 size = AnalyzeBlock(code);
        
        // 分配可执行内存
        u8 *buffer = AllocateExecutableMemory(size * 16);
        
        // 编译MIPS指令到本地代码
        for (u32 i = 0; i < size; i++) {
            CompileInstruction(code[i], buffer);
        }
        
        // 缓存编译结果
        blockCache_[startAddress] = buffer;
    }
    
private:
    std::unordered_map<u32, u8*> blockCache_;
};

2. 音频处理系统

text

class AudioMixer {
public:
    void MixSamples(float *output, int numSamples) {
        std::lock_guard<std::mutex> lock(mutex_);
        
        for (int i = 0; i < numSamples; i++) {
            float sample = 0.0f;
            
            // 混合所有音频源
            for (auto &source : sources_) {
                sample += source->GetNextSample();
            }
            
            // 应用音量控制和限幅
            output[i] = Clamp(sample * volume_, -1.0f, 1.0f);
        }
    }
    
    void AddSource(AudioSource *source) {
        sources_.push_back(source);
    }
    
private:
    std::vector<AudioSource*> sources_;
    std::mutex mutex_;
    float volume_ = 1.0f;
};

3. 内存管理

text

class Memory {
public:
    void Init() {
        // 分配PSP内存空间（32MB）
        ram_ = new u8[32 * 1024 * 1024];
        vram_ = new u8[2 * 1024 * 1024];
        
        // 设置内存映射
        SetupMemoryMap();
    }
    
    u8 *GetPointer(u32 address) {
        if (address < 0x04000000) {
            return &ram_[address];
        } else if (address >= 0x04000000 && address < 0x05000000) {
            return &vram_[address - 0x04000000];
        }
        return nullptr;
    }
    
    u32 Read32(u32 address) {
        u8 *ptr = GetPointer(address);
        if (ptr) {
            return *(u32*)ptr;
        }
        return 0;
    }
    
private:
    u8 *ram_;
    u8 *vram_;
};

构建系统配置

PPSSPP使用CMake作为构建系统，支持跨平台编译：

text

# CMakeLists.txt 示例片段
cmake_minimum_required(VERSION 3.10)
project(PPSSPP)

set(CMAKE_CXX_STANDARD 11)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

# 平台检测
if(WIN32)
    add_definitions(-DWIN32_LEAN_AND_MEAN)
elseif(APPLE)
    find_library(COCOA_LIBRARY Cocoa)
elseif(UNIX AND NOT APPLE)
    find_package(X11 REQUIRED)
endif()

# 添加源代码
add_subdirectory(Core)
add_subdirectory(UI)
add_subdirectory(ext)

# 可执行文件
add_executable(ppsspp ${SOURCES})
target_link_libraries(ppsspp core ui ${PLATFORM_LIBS})

性能优化技巧

1. 缓存友好设计

text

class TextureCache {
public:
    Texture *GetTexture(u32 address) {
        // 使用哈希表快速查找
        auto it = cache_.find(address);
        if (it != cache_.end()) {
            return it->second;
        }
        
        // 缓存未命中，创建新纹理
        Texture *tex = CreateTexture(address);
        cache_[address] = tex;
        return tex;
    }
    
private:
    std::unordered_map<u32, Texture*> cache_;
    const size_t MAX_CACHE_SIZE = 1000;
};

2. SIMD优化

text

#ifdef _M_SSE
#include <emmintrin.h>

void ProcessAudioSSE(float *buffer, int samples) {
    for (int i = 0; i < samples; i += 4) {
        __m128 data = _mm_load_ps(&buffer[i]);
        __m128 processed = _mm_mul_ps(data, _mm_set1_ps(volume_));
        _mm_store_ps(&buffer[i], processed);
    }
}
#endif