我从Vulkan共享了一个Win32句柄，并在OpenGL中创建了一个共享纹理，如下所示：

#ifdef WIN32
        texGl.handle = device.getMemoryWin32HandleKHR({ info.memory, vk::ExternalMemoryHandleTypeFlagBits::eOpaqueWin32 });
#else
        texGl.handle = device.getMemoryFdKHR({ info.memory, vk::ExternalMemoryHandleTypeFlagBits::eOpaqueFd });
#endif
        GLASSERT(texGl.handle);
        auto req = device.getImageMemoryRequirements(texGl.texVk.image);
        // Create a 'memory object' in OpenGL, and associate it with the memory allocated in Vulkan
        glCreateMemoryObjectsEXT(1, &texGl.memoryObject);
#ifdef WIN32
        glImportMemoryWin32HandleEXT(texGl.memoryObject, req.size, GL_HANDLE_TYPE_OPAQUE_WIN32_EXT, texGl.handle);
#else
        glImportMemoryFdEXT(texGl.memoryObject, req.size, GL_HANDLE_TYPE_OPAQUE_FD_EXT, texGl.handle);
        // fd got consumed
        //texGl.fd = -1;
#endif
        glCreateTextures(GL_TEXTURE_2D, 1, &texGl.oglId);
        GLCALL(glTextureStorageMem2DEXT(texGl.oglId, texGl.mipLevels, format, texGl.imgSize.width, texGl.imgSize.height, texGl.memoryObject, info.offset));

那么
我使用copy，例如：

glCopyImageSubData(hsrcTex, GL_TEXTURE_2D, 0, 0, 0, 0, hDesTex,
            GL_TEXTURE_2D, 0, 0, 0, 0, width, height, 1);

然后我得到图像数据，比如：

GLsizei size = width * height * pixsize;
        GLubyte* data = (GLubyte*)malloc(size);
        //(GLuint texture, GLint level, GLenum format, GLenum type, GLsizei bufSize, void *pixels)
        glGetTextureImage(GLuint(desTexture->getID()), 0, (GLenum)desTexture->getFormat(), desTexture->getType(), size, data);
        glGetTextureImage(GLuint(desTexture->getID()), 1, (GLenum)desTexture->getFormat(), desTexture->getType(), size, data);

但是mipMap是任意Nums，则数据为空。
我确信srcTexture有数据可以保存.png文件。我该如何复制呢？？？