如果向下+向右或向上+向左已经按下，则 space 按键没有 SDL 事件

Question

我正在 SDL 的 2D 游戏中试验动作，效果很好。但是，当我添加角色通过按 SPACE 进行射击的可能性时，我遇到了一个奇怪的错误：如果已经按下了向下和向右键或向上和向左键，则在按下 SPACE 时不会创建任何事件.在其他情况下，会创建一个事件，这是应该的。

这是我用来获取一些事件的循环：

while (on == 1)
{
    SDL_PollEvent(&event);
    switch (event.type)
    {
        case SDL_KEYDOWN:
            switch (event.key.keysym.sym)
            {
                case SDLK_ESCAPE:
                    on = 0;
                    break;
                case SDLK_UP:
                    shooter1.dir[0] = 1; // shooter1 is an instance of a structure that
                                         // contains a position and an array representing
                                         // 4 directions (down, up, left, right)
                    break;
                case SDLK_DOWN:
                    shooter1.dir[1] = 1;
                    break;
                case SDLK_LEFT:
                    shooter1.dir[2] = 1;
                    break;
                case SDLK_RIGHT:
                    shooter1.dir[3] = 1;
                    break;
                case SDLK_SPACE:         // Eventually, the program does not go in this
                                         // case, even though the SPACE key is pressed
                    fprintf(stderr, "SPACE PRESSED\n");
                    break;
                default:
                    break;
            }
            break;
        case SDL_KEYUP:
            switch (event.key.keysym.sym)
            {
                case SDLK_UP:
                    shooter1.dir[0] = 0;
                    break;
                case SDLK_DOWN:
                    shooter1.dir[1] = 0;
                    break;
                case SDLK_LEFT:
                    shooter1.dir[2] = 0;
                    break;
                case SDLK_RIGHT:
                    shooter1.dir[3] = 0;
                    break;
                default:
                    break;
            }
            break;
        default:
            break;
    }
    event.type = 0;
    get_new_positions(&shooter1);
    SDL_BlitSurface(background, NULL, screen, &background_pos);
    blit_shooter(screen, &shooter1);
    SDL_Flip(screen);
}

知道这种行为的原因吗？

Answer 1

这几乎可以肯定是硬件限制。引用自the relevant Wikipedia page，重点补充：

Certain high-end keyboards have "n-key rollover". This means that each key is scanned completely independently by the keyboard hardware, so that each keypress is correctly detected regardless of how many other keys are being pressed or held down at the time. [...]

However, to reduce cost and design complexity, most computer keyboards do not isolate all keys in this way. Instead, they use a matrix of key switches, without any isolation diodes, that assumes that only a limited number of keys will be held down at any given time. With these keyboards, pressing as few as three keys can cause ghosting effects, although care is taken when laying out the matrix arrangement that this does not happen for common modifier key combinations.

如果向下+向右或向上+向左已经按下，则 space 按键没有 SDL 事件

No SDL event for space keypress if down+right or up+left already pressed

c

sdl