SDL 2 Space keydown 未检测到，但 Space keyup 工作正常

Question

嘿，我正在开发一个项目/2d 游戏，我在 SDL 中遇到了一些奇怪的行为，我确定这可能是我不理解的。函数 ProcessKeys 被调用，并且对于除 SDLK_SPACE 之外的所有按键按下都可以正常工作，我终生无法弄清楚原因。

更奇怪的是，SDLK_SPACE 的 SDL_KEYUP 开关效果很好。我尝试使用一些调试代码来打印出正在按下哪个键，并且当您按下空格时没有任何寄存器。键盘上的每个其他键都会在 SDL_KEYDOWN 案例顶部的调试语句中注册。

如果有人能看到发生了什么，我将不胜感激。

如果您需要查看它的名称，请告诉我。

SDLKeyboard::KeyState SDLKeyboard::ProcessKeys(SDL_Event * event)
{
switch(event->type)
{
    /* Look for a keypress */
    case SDL_KEYDOWN:
    {
        std::cout << "Key currently pressed" << event->key.keysym.sym << std::endl;
        /* Check the SDLKey values and move change the coords */
            switch(event->key.keysym.sym)
            {
                case SDLK_LEFT:
                {    // rotate the ship left
                    c.setIsTurningLeft(true);
                    return this->keystate = LeftPressed;
                    // add code when user presses left
                    break;
                }
                case SDLK_RIGHT:
                {
                // rotate the ship right
                    c.setIsTurningRight(true);
                    return this->keystate = RightPressed;
                    // add code when user presses right
                    break;
                }
                case SDLK_UP:
                {    
                    // accleration
                    c.setIsAccelerating(true);
                    return this->keystate = UpPressed;
                    // add code when user presses up
                    break;
                }
                case SDLK_SPACE:
                {    
                    // shoot
                    c.setIsShooting(true);
                    std::cout << "keystate = " << this->keystate;
                    return this->keystate = SpacePressed;
                    // add code when user presses space
                    break;
                }
                default:
                {
                    return this->keystate = NotPressed;
                    break;
                }
            }
        break;
    }
    /* We must also use the SDL_KEYUP events to zero the x */
    /* and y velocity variables. But we must also be       */
    /* careful not to zero the velocities when we shouldn't*/
    case SDL_KEYUP:
    {   
        std::cout << "Key currently pressed" << event->key.keysym.sym << std::endl;
        switch(event->key.keysym.sym)
        {
            case SDLK_LEFT:
             {   /* We check to make sure the ship is moving */
                /* to the left. If it is then we zero the    */
                /* velocity. If the ship is moving to the   */
                /* right then the right key is still press   */
                /* so we don't touch the velocity            */
                c.setIsTurningLeft(false);
                return this->keystate = LeftReleased;
                // code to do things when left isn't pushed anymore but still moving left
                break;
            }
            case SDLK_RIGHT:
            {    // code to do things when right isn't pushed anymore but still moving right
                c.setIsTurningRight(false);
                return this->keystate = RightReleased;
                break;
            }
            case SDLK_UP:
            {    // code to do things when up isn't pushed anymore but still moving up
                c.setIsAccelerating(false);
                return this->keystate = UpReleased;
                break;
            }
            case SDLK_SPACE:
            {    // accleration
                c.setIsShooting(false);
                return this->keystate = SpaceReleased;
                // add code when user presses up
                break;
            }
            default:
                break;
        }
        break;
    }
    default:
    {
        return this->keystate = NotPressed;
        break;
    }
 }
}

编辑：

这是请求的示例。我注意到的另一件事是响应延迟不是那么好。就像如果你按下一个键有时控制台不会打印相应的键。可能与我在空间方面遇到的问题有关。

void GUI::TakeInput(SDL_Event *e)
{
    while (SDL_PollEvent(e))
        OnEvent(e);
}
void SDLEvent::OnEvent(SDL_Event * event) 
{
    switch(event->type) 
    {
        case SDL_KEYDOWN: 
        {
            OnKeyDown(event->key.keysym.sym);
            break;
        }

        case SDL_KEYUP:
        {
            OnKeyUp(event->key.keysym.sym);
            break;
        }

        case SDL_MOUSEMOTION:
        {
            OnMouseMove(event->motion.x,event->motion.y);
            break;
        }

        case SDL_MOUSEBUTTONDOWN: 
        {
            OnMouseButtonDown(event->button.button, event->button.x,event->button.y);
            break;
        }

        case SDL_MOUSEBUTTONUP:
        {
            OnMouseButtonUp(event->button.button, event->button.x,event->button.y);
            break;
        }

        case SDL_QUIT: {
            OnExit();
            break;
        }

        case SDL_SYSWMEVENT: {
            //Ignore
            break;
        }

        case SDL_WINDOWEVENT_RESIZED: {
            OnResize();
            break;
        }

        case SDL_WINDOWEVENT_EXPOSED: {
            OnExpose();
            break;
        }

        default: {
            OnUser(event->user.type,event->user.code,event->user.data1,event->user.data2);
            break;
        }
    }
}

void GUI::Play()
{
    Uint32 start_ticks = SDL_GetTicks();
    TakeInput(this->setup->GetEvent());
    this->keyboard->ProcessKeys(this->setup->GetEvent());
    this->setup->RenderBegin();
    this->ship->drawBackBuffer();
    this->ship->renderSprite();
    Uint32 end_ticks = SDL_GetTicks();
    int sleep_delay = (1000 / 60) - (end_ticks-start_ticks);

     if (sleep_delay > 0) {
      SDL_Delay(sleep_delay);
     }     
}

Answer 1

如果你只是在控制台上写event->key.keysym.sym，你应该知道空格键会产生一个几乎看不见的字符。

试试这个：

std::cout << "<" << event->key.keysym.sym << ">"

所以你可以看到尖括号之间印有什么不可见的字符。