Question

（请参阅下面的“编辑2”以获得解决方案。）

我需要从头开始创建SDL表面，而不是从文件中加载它们。不幸的是，与SDL_BlitSurface()生成的曲面一起使用时，SDL_CreateRGBSurface()似乎会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;
}

我得到的是黑色屏幕，而不是100x100蓝色矩形。我可以通过谷歌找到的东西似乎没有帮助我，因为这些问题要么适用于8位表面（并设置调色板 - 我的bpp在这里是32）或者没有得到答案。

所以，我想知道如何将生成的表面正确地blit到SDL屏幕上。

编辑：我看到参数排序中出错了。有问题的行应该阅读

SDL_BlitSurface(layer, NULL, screen, NULL);

但是，我在更复杂的C ++程序中遇到了同样的问题。我将在此处发布代码的相关部分：

main.cpp中：

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，但它显示为黑色。文件selection.bmp也全黑。

编辑2：我发现了造成问题的原因。 selectionRect相对于屏幕设置，而selectionCanvas具有特定菜单项的宽度和高度。因此，填充是在selectionCanvas的范围之外完成的。为填充添加单独的SDL_Rect解决了这个问题。

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);

Answer 1

您反转了来源和目的地。要在屏幕上进行blit，它应该是

SDL_BlitSurface(layer, NULL, screen, NULL);

doc for SDL_BlitSurface

如何正确使用SDL_BlitSurface（）与SDL_CreateRGBSurface（）？

1 个答案: