SDL Surface 返回 NULL？答案

【问题标题】：SDL Surface returning NULL?SDL Surface 返回 NULL？
【发布时间】：2017-05-09 01:47:01
【问题描述】：

我遇到了分段错误，我已将其跟踪到我的表面，它为 NULL（但未触发就地检查）。

我不确定我是否正确地创建了表面。在创建 Surface 时我需要添加什么，我错过了什么？

bool init()
{
    //Initialize SDL
    if( SDL_Init( SDL_INIT_VIDEO ) < 0 )
    {
        printf( "SDL could not initialize! SDL Error: %s\n", SDL_GetError() );
        return false;
    }
    else
    {
        //Set texture filtering to linear
        if( !SDL_SetHint( SDL_HINT_RENDER_SCALE_QUALITY, "1" ) )
        {
            printf( "Warning: Linear texture filtering not enabled!" );
            return false;
        }
        else
        {
            //Create window
            gWindow = SDL_CreateWindow( "kPaint", 575, SDL_WINDOWPOS_UNDEFINED, SCREEN_WIDTH, SCREEN_HEIGHT, SDL_WINDOW_SHOWN );
            GUI = SDL_CreateWindow( "GUI", 0, SDL_WINDOWPOS_UNDEFINED, 573, 542, SDL_WINDOW_SHOWN );

            if( gWindow == NULL || GUI == NULL )
            {
                printf( "Window could not be created! SDL Error: %s\n", SDL_GetError() );
                return false;
            }
            else
            {
                //Create renderer for window
                gRenderer = SDL_CreateRenderer( gWindow, -1, SDL_RENDERER_ACCELERATED );

                if( gRenderer == NULL )
                {
                    printf( "Renderer could not be created! SDL Error: %s\n", SDL_GetError() );
                    return false;
                }
                surface = SDL_GetWindowSurface( gWindow );
                GUIsurface = SDL_GetWindowSurface( GUI );

                if( surface == NULL )
                {
                    printf( "surface could not be created!" );
                    return false;
                }
                SDL_FillRect(surface, NULL, SDL_MapRGB(surface->format, 255,255,255));

                //Initialize PNG loading
                int imgFlags = IMG_INIT_PNG;
                if( !( IMG_Init( imgFlags ) && imgFlags ) )
                {
                    printf( "SDL_image could not initialize! SDL_image Error: %s\n", IMG_GetError() );
                    return false;
                }

            }
        }
    }
    return true;
}

【问题讨论】：

尽量不要在 SDL_GetWindowSurface() 之前创建渲染器。我可能错了，但 iirc SDL 不允许您在为该窗口创建渲染器后获取窗口表面
如果它不是在创建后立即为空，但稍后为空，则您必须在其间进行了更改。
此外，您可以检查 SDL_FillRect() 的返回值，看看那里是否有问题
非常感谢你们，伙计们。我为此感到压力很大。

标签： c++ c sdl sdl-2

【解决方案1】：

谢谢 NeoAgglos。

我在表面之前创建了一个渲染器。

bool init()
{
    //Initialize SDL
    if( SDL_Init( SDL_INIT_VIDEO ) < 0 )
    {
        printf( "SDL could not initialize! SDL Error: %s\n", SDL_GetError() );
        return false;
    }
    else
    {
        //Set texture filtering to linear
        if( !SDL_SetHint( SDL_HINT_RENDER_SCALE_QUALITY, "1" ) )
        {
            printf( "Warning: Linear texture filtering not enabled!" );
            return false;
        }
        else
        {
            //Create window
            gWindow = SDL_CreateWindow( "kPaint", 575, SDL_WINDOWPOS_UNDEFINED, SCREEN_WIDTH, SCREEN_HEIGHT, SDL_WINDOW_SHOWN );
            GUI = SDL_CreateWindow( "GUI", 0, SDL_WINDOWPOS_UNDEFINED, 573, 542, SDL_WINDOW_SHOWN );

            if( gWindow == NULL || GUI == NULL )
            {
                printf( "Window could not be created! SDL Error: %s\n", SDL_GetError() );
                return false;
            }
            else
            {
                surface = SDL_GetWindowSurface( gWindow );
                GUIsurface = SDL_GetWindowSurface( GUI );

                if( surface == NULL )
                {
                    printf( "surface could not be created!" );
                    return false;
                }
                SDL_FillRect(surface, NULL, SDL_MapRGB(surface->format, 255,255,255));

                //Create renderer for window
                gRenderer = SDL_CreateRenderer( gWindow, -1, SDL_RENDERER_ACCELERATED );
                if( gRenderer == NULL )
                {
                    printf( "Renderer could not be created! SDL Error: %s\n", SDL_GetError() );
                    return false;
                }

                //Initialize PNG loading
                int imgFlags = IMG_INIT_PNG;
                if( !( IMG_Init( imgFlags ) && imgFlags ) )
                {
                    printf( "SDL_image could not initialize! SDL_image Error: %s\n", IMG_GetError() );
                    return false;
                }
            }
        }
    }
    return true;
}

【讨论】：

你不能那样做。您欺骗了 SDL 的内部错误检查，但它并没有使其正确。 SDL_GetWindowSurface 的 SDL 手册明确指出您不能将其与渲染 API 混合使用。