如何自动扩展我的OpenGL ES 2.0窗口？

void resize(int width, int height) {
    glViewport(0, 0, width, height);
}

SDL_Window *window;
SDL_GLContext glcontext;

int main(int argc, char *argv[]) {
    SDL_Init(SDL_INIT_VIDEO);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 2);
    SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 0);
    window = SDL_CreateWindow("OpenGL ES 2.0", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 640, 480, SDL_WINDOW_OPENGL | SDL_WINDOW_RESIZABLE);
    glcontext = SDL_GL_CreateContext(window);

    while (1) {
        SDL_Event event;
        while (SDL_PollEvent(&event)) {
            if (event.type == SDL_QUIT) {
                exit(0);
            } else if (event.type == SDL_WINDOWEVENT && event.window.event == SDL_WINDOWEVENT_SIZE_CHANGED) {
                int width = event.window.data1;
                int height = event.window.data2;
                resize(width, height);
            }
        }

        // 渲染代码

        SDL_GL_SwapWindow(window);
    }

    SDL_GL_DeleteContext(glcontext);
    SDL_DestroyWindow(window);
    SDL_Quit();
    return 0;
}