如何将SDL_BlitSurface(）与SDL_CreateRGBSurface(）一起正确使用

（有关解决方案，请参阅下面的"编辑2"。）

我需要从头开始创建SDL曲面，而不是从文件中加载它们。不幸的是，当与通过SDL_CreateRGBSurface()生成的曲面一起使用时，SDL_BlitSurface()似乎将所有颜色渲染为黑色。这是我的代码：

int main(int argc, char** argv)
{
    SDL_Surface* screen = SDL_SetVideoMode(640, 480, 32, SDL_HWSURFACE);
    SDL_Surface* layer = SDL_CreateRGBSurface(SDL_HWSURFACE, 100, 100,
        screen->format->BitsPerPixel,
        screen->format->Rmask,
        screen->format->Gmask,
        screen->format->Bmask,
        screen->format->Amask
    );
    SDL_Rect rect;
    rect.x = 0;
    rect.y = 0;
    rect.w = 100;
    rect.h = 100;
    Uint32 blue = SDL_MapRGB(screen->format, 0, 0, 255);
    SDL_FillRect(layer, &rect, blue);
    SDL_BlitSurface(screen, NULL, layer, NULL);
    SDL_Flip(screen);
    SDL_Delay(3000);
    return 0;
}

我得到的是一个黑色屏幕，而不是一个100x100的蓝色矩形。我在谷歌上搜索到的似乎对我没有帮助，因为这些问题要么适用于8位曲面（以及设置调色板——我的bpp在这里是32），要么没有答案。

所以，我想知道我应该如何正确地将生成的曲面闪电战到SDL屏幕上。

编辑：我看到这是参数排序中的一个错误。有问题的行应该是

SDL_BlitSurface(layer, NULL, screen, NULL);

尽管如此，我还是很难在我更复杂的C++程序中实现同样的效果。我将在这里张贴代码的相关部分：

main.cpp:

int main(int argc, char** argv)
{
    SDLScreen screen(1024, 700, "Hello, SDL!");
SDL_Event event;
    SDLMenu menu;
    bool shouldQuit = false;
    menu.setBounds(200, 100, 200, 600);
    menu.setFontName("NK211.otf");
    menu.setFontSize(36);
    menu.setEffect(sdlteShadowText);
    menu.addItem("New game");
    menu.addItem("Load game");
    menu.addItem("Save game");
    menu.addItem("Exit");
    menu.render();
    while (!shouldQuit)
    {
        menu.draw(screen.getSurface());
        SDL_Flip(screen.getSurface());
        SDL_Delay(10);
        while (SDL_PollEvent(&event))
        {
            if (event.type == SDL_QUIT)
            {
                shouldQuit = true;
            }
            else if (event.type == SDL_KEYUP)
            {
                if (event.key.keysym.sym == SDLK_q)
                {
                    shouldQuit = true;
                }
            }
        }
    }
}

SDLMenu.cpp:

void
SDLMenu::setSelectionColorRGB(int r, int g, int b)
{
    SDL_VideoInfo* info = (SDL_VideoInfo*)SDL_GetVideoInfo();
    selectionColor = SDL_MapRGB(info->vfmt, r, g, b);
}
void
SDLMenu::render()
{
    SDLText* current = NULL;
    SDL_VideoInfo* info = (SDL_VideoInfo*)SDL_GetVideoInfo();
    if (!items->empty())
    {
        current = getItemAt(currentItem);
        selectionRect = getItemRect(current);
        setSelectionColorRGB(0,0,255);
        selectionCanvas = SDL_CreateRGBSurface(SDL_HWSURFACE,
            selectionRect->w, selectionRect->h,
            info->vfmt->BitsPerPixel,
            info->vfmt->Rmask,
            info->vfmt->Gmask,
            info->vfmt->Bmask,
            info->vfmt->Amask);
        SDL_FillRect(selectionCanvas, selectionRect, selectionColor);
        SDL_SaveBMP(selectionCanvas, "selection.bmp"); // debug
    }
    for (list<SDLText*>::iterator i = items->begin();
        i != items->end(); i++)
    {
        (*i)->render();
    }
}
void
SDLMenu::draw(SDL_Surface* canvas)
{
    int currentY = bounds.y;
    if (selectionCanvas != NULL)
    {
        SDL_BlitSurface(selectionCanvas, NULL, canvas, selectionRect);
    }
    for (list<SDLText*>::iterator i = items->begin();
        i != items->end(); i++)
    {
        (*i)->draw(bounds.x, currentY, canvas);
        currentY += fontSize + itemGap;
    }
}

SDLScreen.cpp:

SDLScreen::SDLScreen(int w, int h, string t, int d)
    : width(w), height(h), depth(d), title(t)
{
    SDL_Init(SDL_INIT_EVERYTHING);
    SDL_WM_SetCaption(title.c_str(), NULL);
    refresh();
}
void
SDLScreen::refresh()
{
    screen = SDL_SetVideoMode(width, height, 32, SDL_HWSURFACE);
}

活动菜单项的选择矩形应为蓝色，但显示为黑色。文件selection.bmp也是全黑的。

编辑2:我发现了问题的根源。selectionRect是相对于屏幕设置的，而selectionCanvas具有特定菜单项的宽度和高度。因此，填充是在selectionCanvas的边界之外进行的。添加单独的SDL_Rect进行填充解决了问题。

SDL_Rect fillRect;
fillRect.x = 0;
fillRect.y = 0;
fillRect.w = selectionRect->w;
fillRect.h = selectionRect->h;
SDL_FillRect(selectionCanvas, &fillRect, selectionColor);
// and later...
SDL_BlitSurface(selectionCanvas, NULL, canvas, selectionRect);