SDL_BlitSurface（）返回-1 ...爲什麼？

SDL文檔說SDL_BlitSurface（）在不成功時返回-1，但我找不到爲什麼會失敗。SDL_BlitSurface（）返回-1 ...爲什麼？

這裏是我的源代碼：

的main.cpp

#include <iostream> 
#include <string> 
#include <SDL/SDL.h> 
#include <SDL/SDL_image.h> 
#include "window.cpp" 
#include "player.cpp" 

int init(); 
void quit(); 

int main(int argc,char *args[]) 
{ 
    if (init() == -1) 
    { 
     std::cerr << "Error:init()" << std::endl; 
     return -1; 
    } 
    window main_window("Juego","img/bg.png",800,600,32); 
    player player1(500,500,0,0,5,5,"img/square.png"); 
    while (!main_window.close) 
    { 
     main_window.handle_events(); 
     if (main_window.draw_background() != true) 
     { 
      std::cerr << "ERROR->main_window.draw_background()" << std::endl; 
      main_window.close = true; 
     } 
     player1.update(main_window.screen); 
     SDL_Flip(main_window.screen); 
     SDL_Delay(60/1000); 
    } 
    quit(); 
    return 0; 
} 

int init() 
{ 
    if (SDL_Init(SDL_INIT_EVERYTHING) == -1) 
    { 
     std::cerr << "Error while initialising SDL" << std::endl; 
     return -1; 
    } 
    return 0; 
} 

void quit() 
{ 
    SDL_Quit(); 
}

window.cpp

class window 
{ 
    private: 
     void load_image(std::string source,SDL_Surface *destination); 
     SDL_Surface *window_bg; 
     SDL_Event event_queue; 
     SDL_Rect window_rect; 
    public: 
     window(std::string SCREEN_TITLE,std::string SCREEN_BG,int sw,int sh,int sbpp); 
     void handle_events(); 
     bool draw_background(); 
     SDL_Surface *screen; 
     bool close; 
}; 

window::window(std::string SCREEN_TITLE,std::string SCREEN_BG,int sw,int sh,int sbpp) 
{ 
    window_bg = NULL; 
    screen = NULL; 
    close = false; 
    window_rect.x = 0; 
    window_rect.y = 0; 
    window_rect.w = sw; 
    window_rect.h = sh; 
    screen = SDL_SetVideoMode(sw,sh,sbpp,SDL_SWSURFACE); 
    std::cout << "Screen created." << std::endl; 
    SDL_WM_SetCaption(SCREEN_TITLE.c_str(),NULL); 
    std::cout << "Window title: " << SCREEN_TITLE << std::endl; 
    load_image(SCREEN_BG,window_bg); 
} 

void window::handle_events() 
{ 
    while (SDL_PollEvent(&event_queue)) 
    { 
     if (event_queue.type == SDL_QUIT) 
     {  
      close = true; 
     } 
    } 
} 

void window::load_image(std::string source,SDL_Surface *destination) 
{ 
    SDL_Surface *tmp_img = IMG_Load(source.c_str()); 
    if (tmp_img != NULL) 
    { 
     if ((destination = SDL_DisplayFormat(tmp_img)) == NULL) 
     { 
      std::cerr << "ERROR->SDL_DisplayFormat()" << std::endl; 
     } 
     std::cout << source << " Loaded." << std::endl; 
     SDL_FreeSurface(tmp_img); 
    } 
    else 
    {  
     std::cerr << "Could not load: " << source << std::endl; 
    } 
} 

bool window::draw_background() 
{ 
    int error_check = SDL_BlitSurface(window_bg,&window_rect,screen,NULL); 
    if (error_check != 0) 
    { 
     std::cerr << "SDL_BlitSurface() == " << error_check << std::endl; 
     return false; 
    } 
    return true; 
}

的錯誤是在window.cpp（我認爲）：

bool window::draw_background() 
{ 
    int error_check = SDL_BlitSurface(window_bg,NULL,screen,NULL); 
    if (error_check != 0) 
    { 
     std::cerr << "SDL_BlitSurface() == " << error_check << std::endl; 
     return false; 
    } 
    return true; 
}

我的程序輸出是：

Screen created. 
Window title: Juego 
img/bg.png Loaded. 
img/square.png Loaded 
SDL_BlitSurface() == -1 
ERROR->main_window.draw_background()

來源

2012-04-23 juiko

load_image(SCREEN_BG,window_bg);在窗口構造函數加載到一個臨時的SDL_Surface中，永遠不會填充destination，我假設它是一個輸出參數。然後當draw_background()使用window_bg時，它仍然是NULL。

來源

2012-04-24 01:35:31 dgnorton

任何事情都可能是這個原因（我都快不懂得通過您的代碼看，見http://sscce.org/），可以調試出了什麼問題通過在錯誤的返回值打印出來SDL_GetError()。

來源

2012-04-24 00:03:04 orlp

對不起，我認爲我的代碼不是那麼大，所以我只是複製並粘貼它...無論如何，我認爲我已經修復了錯誤，在我的窗口類構造函數我有window_bg = NULL;我刪除它，現在SDL_BlitSurface（）似乎工作正常。但是沒有任何東西可以畫到屏幕上。 – juiko 2012-04-24 00:57:44

SDL_BlitSurface（）返回-1 ...爲什麼？

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