Question

我试图在C中写一个简单的游戏。我使用SDL2绘制东西。这是一个主循环：

...
while( !quit_f )
{
    //Handle events on queue
    while( SDL_PollEvent( &e ) != 0 )
    {
        //User requests quit
        if( e.type == SDL_QUIT )
        {
            quit_f = 1;
        }
    }
    currTime = clock();
    dt = (float)((currTime - t)/1000.0f);
    update_player(dt, player);

    printf("locks before drawing: %i\n", player->surface->locked );
    draw_player(player);

    printf("\n");
    printf("%p\n", player->surface);
    printf("locks before window update: %i\n", player->surface->locked );

    //Update window surface
    SDL_UpdateWindowSurface( window );

    printf("%s\n", SDL_GetError());
    printf("locks after window update: %i\n", player->surface->locked );
    printf("\n");
    t = currTime;
}
...

这是draw_player函数：

void draw_player(struct GameObject * self){
    printf("%p\n", self->surface);
    printf("locks iside draw_player - before blit: %p\n", self->surface->locked);
    SDL_BlitSurface(window, NULL, self->surface, NULL);
    printf("locks iside draw_player - after blit: %p\n", self->surface->locked);
}

它编译得很好但运行后它不会显示播放器。输出：

locks before drawing: 0
0x89795b0
locks iside draw_player - before blit: (nil)
locks iside draw_player - after blit: (nil)

0x89795b0
locks before window update: 0
Surfaces must not be locked during blit
locks after window update: 0

我不明白为什么在draw_player函数中self->surface->locked为NULL。表面上的指针是相同的，所以...我真的不明白。我没有在我的代码中的任何地方调用SDL_LockSurface，但SDL抱怨表面在blit期间被锁定 - Surfaces must not be locked during blit。我试图在SDL_BlitSurface之前调用SDL_UnlockSurface但没有任何改变。有任何想法吗？我必须注意到我在C和SDL中更好。我运行Fedora 24.由于SDL是跨平台的lib，它应该不是问题。我使用gcc 6.1.1。

玩家的精灵是png格式，这就是我使用IMG_Load的原因。以下是玩家的创建方式：

void init_player(struct GameObject * player, char * path, float x, float y){
    SDL_Surface * image = IMG_Load(path);
    if(image == NULL){
        printf("Error while loading png: %s\n", IMG_GetError()); 
        return;
    }

    // direction vector
    player_dir = malloc(sizeof(Vector2d));
    player_dir->x = 0.0f; 
    player_dir->y = 0.0f;

    // destination rectangle
    SDL_Rect * dRect = malloc(sizeof(SDL_Rect));
    dRect->x = round(x);
    dRect->y = round(y);
    dRect->w = image->w;
    dRect->h = image->h;

    player->surface = image;
    player->destRect = dRect;
    player->x = x;
    player->y = y;
    player->width = image->w;
    player->height = image->h;    
    player->update = update_player; // function pointer
    player->draw = draw_player; // function pointer
}

最后一件事我必须告诉你。我存储指针以在GameObject结构中绘制和更新函数。所以我将update_player称为player->update(...)。绘图功能也是一样的。这有点hacky风格，但我喜欢它。我试着马上打电话给draw_player。由于结果相同，我认为我的编码风格不是问题。但我可能错了。随意纠正我。

编辑：我可能会发现这个bug。 SDL_BlitSurface(window, NULL, self->surface, NULL);应为SDL_BlitSurface(screenSurface, NULL, self->surface, NULL);。 Window是指向SDL_Window的指针，screenSurface是指向SDL_Surface的指针。为什么在编译期间没有抛出错误？好的，错误消失了。但没有任何表现。

编辑没有。 2 我找到了。这是一个愚蠢的错误。这是正确的解决方案：SDL_BlitSurface(self->surface, NULL, screenSurface, NULL); 以下是SDL_BlitSurface的样子：

int SDL_BlitSurface(SDL_Surface*    src,
                const SDL_Rect* srcrect,
                SDL_Surface*    dst,
                SDL_Rect*       dstrect)

首先必须是源表面和第三个目标表面。反过来写的。它造成了一个错误。

SDL - 在blit期间不得锁定曲面

0 个答案: