使用C++在SDL中顯示.png文件

Question

用C++編寫：我試圖讓一匹騎士穿過屏幕運行（不知名的「傢伙」）。騎士目前在我的目錄中存在2個.png文件，以模擬一些動畫不佳的舞動。當他是.bmp時，我能夠讓他出現，但我想利用png文件的透明度 - 我也嘗試過並且打開tif文件失敗。如何更改我的代碼以便讓他從正確加載到SDL中的.png中出現？這裏是我的.cpp文件：

#include "SDL/SDL.h" 
#include <iostream> 
#include "source_sdl.h" 
# include <string> 

using namespace std; 

int source_sdl(int argc, char* args[]) { 

int switch = 1; 
int running = 1; 

// surface & rect declarations 
SDL_Surface* ground = NULL; 
SDL_Surface* guy = NULL; 
SDL_Surface* guy2 = NULL; 
SDL_Rect guylocationRect; 
SDL_Rect groundlocationRect; 

// initialize SDL & the screen 
SDL_Init(SDL_INIT_EVERYTHING); 
screen = SDL_SetVideoMode(875, 625, 32, SDL_SWSURFACE); 

// open .png files 
SDL_RWops* guy_rwop; 
SDL_RWops* guy2_rwop; 
guy_rwop = SDL_RWFromFile("tiffKnight.png", "rb"); 
guy2_rwop = SDL_RWFromFile("tiffKnight2.png", "rb"); 
guy = IMG_LoadPNG_RW(guy_rwop); 
guy2 = IMG_LoadPNG_RW(guy2_rwop); 
guylocationRect.x = 300; 
guylocationRect.y = 300; 
groundlocationRect.x = 300; 
groundlocationRect.y = 300; 

SDL_Event occur; 

// animation loop (currently endless) 
while (running == 1){ 

    SDL_Flip(screen); 
    SDL_Delay(300); 

    if (gallop > 89) gallop=0; 

    // draw the ground 
    for(int yu = 0; yu<35; yu++){ 
     groundlocationRect.x=25*yu; 
     groundlocationRect.y=5*25; 
     SDL_BlitSurface(ground, NULL, screen, &groundlocationRect); 
    } 
    // draw the gallopping 
    guylocationRect.x=10*gallop; 
    guylocationRect.y=5*25; 
    if(switch){ 
     SDL_BlitSurface(guy, NULL, screen, &guylocationRect); 
    }else{ 
     SDL_BlitSurface(guy2, NULL, screen, &guylocationRect); 
    } 
    gallop++; 
    switch = (switch+1)%2; 
    for(int u = 6; u < 25; u++){ 
     for(int yu = 0; yu < 35; yu++){ 
      groundlocationRect.x = 25*yu; 
      groundlocationRect.y = 25*u; 
      SDL_BlitSurface(ground, NULL, screen, &groundlocationRect); 
     } 
    } 
} 
SDL_FreeSurface(guy); 
SDL_FreeSurface(guy2); 
SDL_FreeSurface(ground); 
} 

正如我現在有它，騎士不會出現，我收到任何錯誤故障檢查，如

if(!guy) { 
    cout << "IMG_LoadPNG_RW: %s\n" << IMG_GetError(); 
} 

（SDL的屏幕是開放的後果是什麼？）

也沒有收到任何結果。我的.h文件很簡單：

#include "SDL/SDL.h" 
#include <iostream> 

using namespace std; 
int source_sdl(int argc, char* args[]); 

而且我的main.cpp：

#include "SDL/SDL.h" 
#include <iostream> 
#include "source_sdl.h" 
using namespace std; 

int main(int argc, char* args[]){ 

    source_sdl(argc, args); 

} 

任何有識之士將是美好的，因爲這騎士最終應該是在一個塔防遊戲的敵人！先謝謝你！

這是從我如何對不同類型的文件加載到SDL信息的頁面：http://www.libsdl.org/projects/SDL_image/docs/SDL_image.html#SEC24

Answer 1

如果你真的想堅持用C++ SDL，我建議你使用SDL_image library和使用功能，如：

SDL_Surface * load_image(std::string const & filename) 
{ 
    SDL_Surface * tmp; 
    SDL_Surface * img; 

    img = NULL; 
    if ((tmp = IMG_Load(filename.c_str()))) 
    { 
     img = SDL_DisplayFormatAlpha(tmp); 
     SDL_FreeSurface(tmp); 
    } 
    return img; 
} 

如果使用庫需要一個更加現代化和安全的方法：

surface_ptr load_image (std::string const & filename) 
{ 
    using surface_ptr = std::unique_ptr<SDL_Surface, decltype(SDL_FreeSurface) *>; 

    surface_ptr img { nullptr, SDL_FreeSurface }; 
    surface_ptr tmp { IMG_Load(filename.c_str()), SDL_FreeSurface }; 

    if (tmp) 
     img.reset(SDL_DisplayFormatAlpha(tmp.get())); 

    return img; 
}