OpenGL使用FreeImage保存屏幕截图

说明

  • 给现有模拟平台集成保存当前时刻OpenGL渲染屏幕截图
  • 环境：Windows 10，Visual Studio 2019，C++

准备

下载FreeImage库，http://freeimage.sourceforge.net/download.html

打开sln，编译FreeImageLib这个项目（设为启动项），根据debug/release版本选择编译。

环境配置:

2019安装目录：

C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.28.29333
ps：路径会因版本不同稍有区别

  • 首先把FreeImage.h 头文件拷贝至在"VS安装目录"/VC/include/
  • 把FreeImage.lib静态库拷贝到"VS安装目录"**/VC/lib/**中；
  • 最后，把FreeImage.dll动态链接库放在应用程序的目录下，一般为VS工程的bin目录

使用前加上

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#pragma comment(lib, "FreeImage.lib")

使用

实际需求的代码实现片段

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{
    std::string exportPath = FileSystem::normalizePath(m_outputPath + "/img");
    FileSystem::makeDirs(exportPath);
    //glReadPixels
    std::string picName = "pic_";
    picName = picName + std::to_string(m_frameCounter) + ".png";
    std::string exportPicName = FileSystem::normalizePath(exportPath + "/" + picName);

    int width = 1280;
    int height = 960;

    unsigned char* mpixels = new unsigned char[width * height * 4];
    glReadBuffer(GL_FRONT);
    glReadPixels(0, 0, width, height, GL_RGBA, GL_UNSIGNED_BYTE, mpixels);
    for (int i = 0; i < (int)width * height * 4; i += 4)
    {
        mpixels[i] ^= mpixels[i + 2] ^= mpixels[i] ^= mpixels[i + 2];
    }
    
    FIBITMAP* bitmap = FreeImage_Allocate(width, height, 32, 8, 8, 8);

    for (int y = 0; y < FreeImage_GetHeight(bitmap); y++)
    {
        BYTE* bits = FreeImage_GetScanLine(bitmap, y);
        for (int x = 0; x < FreeImage_GetWidth(bitmap); x++)
        {
            bits[0] = mpixels[(y * width + x) * 4 + 0];
            bits[1] = mpixels[(y * width + x) * 4 + 1];
            bits[2] = mpixels[(y * width + x) * 4 + 2];
            bits[3] = 255;
            bits += 4;
        }

    }
    bool bSuccess = FreeImage_Save(FIF_PNG, bitmap, exportPicName.c_str(), PNG_DEFAULT);
    FreeImage_Unload(bitmap);
}

网上的保存为jpg参考代码

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{
    unsigned char *mpixels = new unsigned char[WIDTH * HEIGHT * 3];
    glReadBuffer(GL_FRONT);
    glReadPixels(0, 0, WIDTH, HEIGHT, GL_RGB, GL_UNSIGNED_BYTE, mpixels);
    glReadBuffer(GL_BACK);
    for(int i = 0; i < (int)WIDTH*HEIGHT*3; i += 3)
    {   
        mpixels[i] ^= mpixels[i+2] ^= mpixels[i] ^= mpixels[i+2];
    }
    FIBITMAP* bitmap = FreeImage_Allocate(WIDTH, HEIGHT, 24, 8, 8, 8);
 
    for(int y = 0 ; y < FreeImage_GetHeight(bitmap); y++)
    {
        BYTE *bits = FreeImage_GetScanLine(bitmap, y);
        for(int x = 0 ; x < FreeImage_GetWidth(bitmap); x++)
        {
            bits[0] = mpixels[(y*WIDTH+x) * 3 + 0];
            bits[1] = mpixels[(y*WIDTH+x) * 3 + 1];
            bits[2] = mpixels[(y*WIDTH+x) * 3 + 2];
            bits += 3;
        }
 
    }
 
    FreeImage_Save(FIF_JPEG, bitmap, "test.jpg", JPEG_DEFAULT);
 
    FreeImage_Unload(bitmap);
}