Linux 中的 SDL2 空透明 window

Question

这是我尝试在我的 Linux 计算机运行ning Ubuntu 18.04 上运行使用 KDE Plasma 桌面环境（我有多个桌面环境）的一些示例 SDL2 代码安装以防相关):

#include<iostream>
#include<SDL2/SDL.h>

int main(int argc, char** argv)
{
    if(SDL_Init(SDL_INIT_VIDEO) != 0){
        std::cerr << "SDL_Init() Error: " << SDL_GetError() << std::endl;
        return 1;
    }

    SDL_Window* win = SDL_CreateWindow(
        "Hello world",
        SDL_WINDOWPOS_CENTERED,
        SDL_WINDOWPOS_CENTERED,
        640,480,
        0
    );

    if(win == nullptr){
        std::cerr << "SDL_CreateWindow() Error: " << SDL_GetError() << std::endl;
        return 1;  
    }

    //Create and init the renderer
    SDL_Renderer* ren = SDL_CreateRenderer(win, -1, 0);
    if(ren == nullptr){
        std::cerr << "SDL_CreateRenderer() Error: " << SDL_GetError() << std::endl;
        SDL_DestroyWindow(win);
        return 1;
    }

    //Render something
    SDL_RenderSetLogicalSize(ren,640,480);

    //Set colour of renderer
    SDL_SetRenderDrawColor(ren,255,0,0,255);

    //Clear the screen to the set colour
    SDL_RenderClear(ren);

    //Show all the has been done behind the scenes
    SDL_RenderPresent(ren);

    //Delay so that we can see what is on the screen
    SDL_Delay(5000);

    //Clean Up
    SDL_DestroyRenderer(ren);
    SDL_DestroyWindow(win);
    SDL_Quit();

    return 0;
}

本该出现的红色window只在我运行程序第一次出现的时候出现了一次。所有后续执行都会产生一个空的 t运行sparent window 以及背景中的任何内容。背景图像随 window.

一起拖动

我在 SDL_CreateWindow() 中尝试了 SDL_WINDOW_SHOWN 标志，在 SDL_CreateRenderer() 中尝试了 SDL_RENDER_ACCELERATED 标志。

再次出现红屏的唯一方法是重启系统。

我什至用 IDE (CodeLite) 编译并运行这个，我仍然得到相同的结果。

SO 上的这个特定问题显示了类似的问题。但是 OP 没有使用 Linux 并且问题并不完全相同。

该网站上的其他帖子提到了事件处理，但我还没有深入了解。如果有必要，我将不胜感激，因为 documentation 解释不多。

更新：此程序运行在另一台计算机运行ning Lubuntu 18.10 上没问题。

Answer 1

用调用 SDL_PumpEvents() 的循环替换 SDL_Delay()（它阻止所有事件处理，例如通知 X11/Wayland 和您的 window 经理您的进程仍然存在）不知何故，直接（如下所示）或间接通过 SDL_PollEvent()/SDL_WaitEvent():

const Uint32 startMs = SDL_GetTicks();
while( SDL_GetTicks() - startMs < 5000 )
{
    SDL_PumpEvents();

    //Render something
    SDL_RenderSetLogicalSize(ren,640,480);

    //Set colour of renderer
    SDL_SetRenderDrawColor(ren,255,0,0,255);

    //Clear the screen to the set colour
    SDL_RenderClear(ren);

    //Show all the has been done behind the scenes
    SDL_RenderPresent(ren);
}

总计：

#include <iostream>
#include <SDL2/SDL.h>

int main( int argc, char** argv )
{
    if( SDL_Init( SDL_INIT_VIDEO ) != 0 )
    {
        std::cerr << "SDL_Init() Error: " << SDL_GetError() << std::endl;
        return 1;
    }

    SDL_Window* win = SDL_CreateWindow
        (
        "Hello world",
        SDL_WINDOWPOS_CENTERED,
        SDL_WINDOWPOS_CENTERED,
        640, 480,
        0
        );

    if( win == nullptr )
    {
        std::cerr << "SDL_CreateWindow() Error: " << SDL_GetError() << std::endl;
        return 1;
    }

    //Create and init the renderer
    SDL_Renderer* ren = SDL_CreateRenderer( win, -1, 0 );
    if( ren == nullptr )
    {
        std::cerr << "SDL_CreateRenderer() Error: " << SDL_GetError() << std::endl;
        SDL_DestroyWindow( win );
        return 1;
    }

    const Uint32 startMs = SDL_GetTicks();
    while( SDL_GetTicks() - startMs < 5000 )
    {
        SDL_PumpEvents();

        //Render something
        SDL_RenderSetLogicalSize( ren, 640, 480 );

        //Set colour of renderer
        SDL_SetRenderDrawColor( ren, 255, 0, 0, 255 );

        //Clear the screen to the set colour
        SDL_RenderClear( ren );

        //Show all the has been done behind the scenes
        SDL_RenderPresent( ren );
    }

    //Clean Up
    SDL_DestroyRenderer( ren );
    SDL_DestroyWindow( win );
    SDL_Quit();

    return 0;
}

Linux 中的 SDL2 空透明 window

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