如何使用SDL一次处理多个按键？

Question

使用c ++在Ubuntu上使用SDL熟悉OpenGL编程.经过一番环顾和实验,我开始明白了.我需要有关SDL键盘事件处理的建议.

我有一个第一人称相机,可以走路,后退,左右扫视,并使用鼠标环顾四周,这是伟大的.这是我的processEvents函数:

void processEvents()
{
    int mid_x = screen_width  >> 1;
int mid_y = screen_height >> 1;
int mpx = event.motion.x;
int mpy = event.motion.y;
float angle_y  = 0.0f;
float angle_z  = 0.0f;

while(SDL_PollEvent(&event))
{
    switch(event.type)
    {
        case SDL_KEYDOWN:
            switch(event.key.keysym.sym)
            {
                case SDLK_ESCAPE:
                    quit = true;
                    break;
                case SDLK_w:
                    objCamera.Move_Camera( CAMERASPEED);
                    break;
                case SDLK_s:
                    objCamera.Move_Camera(-CAMERASPEED);
                    break;
                case SDLK_d:
                    objCamera.Strafe_Camera( CAMERASPEED);
                    break;
                case SDLK_a:
                    objCamera.Strafe_Camera(-CAMERASPEED);
                    break;
                default:
                    break;
            }
            break;

        case SDL_MOUSEMOTION:
            if( (mpx == mid_x) && (mpy == mid_y) ) return;

            SDL_WarpMouse(mid_x, mid_y);

            // Get the direction from the mouse cursor, set a resonable maneuvering speed
            angle_y = (float)( (mid_x - mpx) ) / 1000;      
            angle_z = (float)( (mid_y - mpy) ) / 1000;

            // The higher the value is the faster the camera looks around.
            objCamera.mView.y += angle_z * 2;

            // limit the rotation around the x-axis
            if((objCamera.mView.y - objCamera.mPos.y) > 8)  objCamera.mView.y = objCamera.mPos.y + 8;
            if((objCamera.mView.y - objCamera.mPos.y) <-8)  objCamera.mView.y = objCamera.mPos.y - 8;

            objCamera.Rotate_View(-angle_y);

            break;

        case SDL_QUIT:
            quit = true;
            break;

        case SDL_VIDEORESIZE:
            screen = SDL_SetVideoMode( event.resize.w, event.resize.h, screen_bpp, SDL_OPENGL | SDL_HWSURFACE | SDL_RESIZABLE | SDL_GL_DOUBLEBUFFER | SDL_HWPALETTE );
            screen_width = event.resize.w;
            screen_height = event.resize.h;
            init_opengl();
            std::cout << "Resized to width: " << event.resize.w << " height: " << event.resize.h << std::endl;
            break;

        default:
            break;
    }
}
}

现在,虽然这是有效的,但它有一些局限性.最大的问题和我的问题的目的是它似乎只处理被按下的最新密钥.因此,如果我按住's'向后走,我按'd'向右扫,我最终向右扫射但不向后移动.

有人能指出我正确的方向,以便更好地使用SDL处理键盘,同时支持多个按键等吗？

谢谢

Answer 1

SDL跟踪所有密钥的当前状态.您可以通过以下方式访问此州:

SDL_GetKeyState()

因此,每次迭代都可以根据键状态更新运动.要使运动平稳,您应根据更新之间经过的时间更新运动幅度.

Answer 2

一个好的方法是编写一个键盘("输入")处理程序,它将处理输入事件并将事件的状态保持在某种结构中(关联数组听起来很好 - 键[keyCode]).

每次键盘处理程序收到"按下键"事件时,它都会将键设置为启用(true),当它获得按键事件时,它会将其设置为禁用(false).

然后,您可以一次检查多个键而不直接拉动事件,并且您将能够在整个帧中重复使用键盘,而无需将其传递给子例程.

一些快速伪代码:

class KeyboardHandler {
    handleKeyboardEvent(SDL Event) {
        keyState[event.code] = event.state;
    }

    bool isPressed(keyCode) {
        return (keyState[keyCode] == PRESSED);
    }

    bool isReleased(keyCode) {
        return (keyState[keyCode] == RELEASED);
    }

    keyState[];
}

...

while(SDL Pull events)
{
    switch(event.type) {
        case SDL_KEYDOWN:
        case SDL_KEYUP:
                keyHandler.handleKeyboardEvent(event);
            break;
        case SDL_ANOTHER_EVENT:
                ...
            break;
    }   
}

// When you need to use it:
if(keyHandler.isPressed(SOME_KEY) && keyHandler.isPressed(SOME_OTHER_KEY))
    doStuff(TM);

Answer 3

如果您使用的是 SDL2，则使用SDL_GetKeyboardState.

例子：

const Uint8 *keyboard_state_array = SDL_GetKeyboardState(NULL);

SDL_PollEvent(&event);

if(event.type == SDL_KEYDOWN || event.type == SDL_KEYUP)
{
    // Move centerpoint of rotation for one of the trees:
    if (keyboard_state_array[SDL_SCANCODE_UP] && !(keyboard_state_array[SDL_SCANCODE_DOWN]))
    {
        --location.y;
    }
    else if (!keyboard_state_array[SDL_SCANCODE_UP] && keyboard_state_array[SDL_SCANCODE_DOWN])
    {
        ++location.y;
    }

    if (keyboard_state_array[SDL_SCANCODE_RIGHT] && !keyboard_state_array[SDL_SCANCODE_LEFT])
    {
        ++location.x;
    }
    else if (!keyboard_state_array[SDL_SCANCODE_RIGHT] && keyboard_state_array[SDL_SCANCODE_LEFT])
    {
        --location.x;
    }
}