SDL_image的IMG_Load不起作用

Question

我正在使用 IMG_Load() 加载 png 文件，但它根本不起作用。 loadImage = IMG_Load(文件名.c_str());这句话之后，loadedImage仍然是NULL，没有发生错误。 PS：我使用的是VS C++2008，png文件位于develop文件夹中。这是我的代码：（这正是 Lazy Foo 喜欢的）

//The headers
#include "SDL.h"
#include "SDL_image.h"
#include <string>

#pragma comment( linker, "/subsystem:\"windows\" /entry:\"mainCRTStartup\"" )

//Screen attributes
const int SCREEN_WIDTH = 640;
const int SCREEN_HEIGHT = 480;
const int SCREEN_BPP = 32;

//The surfaces
SDL_Surface *image = NULL;
SDL_Surface *screen = NULL;

SDL_Surface *load_image( std::string filename )
{
    //The image that's loaded
    SDL_Surface* loadedImage = NULL;

    //The optimized image that will be used
    SDL_Surface* optimizedImage = NULL;

    //Load the image using SDL_image
 loadedImage = IMG_Load(filename.c_str());

    //If the image loaded
    if( loadedImage != NULL )
    {
        //Create an optimized image
  //cout<<"Flag";
        optimizedImage = SDL_DisplayFormat( loadedImage );

        //Free the old image
        SDL_FreeSurface( loadedImage );
    }

    //Return the optimized image
    return optimizedImage;
}

void apply_surface( int x, int y, SDL_Surface* source, SDL_Surface* destination )
{
    //Rectangle to hold the offsets
    SDL_Rect offset;

    //Get offsets
    offset.x = x;
    offset.y = y;

    //Blit the surface
    SDL_BlitSurface( source, NULL, destination, &offset );
}

bool init()
{
    //Initialize all SDL subsystems
    if( SDL_Init( SDL_INIT_EVERYTHING ) == -1 )
    {
        return false;
    }

    //Set up the screen
    screen = SDL_SetVideoMode( SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_BPP, SDL_SWSURFACE );

    //If there was an error in setting up the screen
    if( screen == NULL )
    {
        return false;
    }

    //Set the window caption
    SDL_WM_SetCaption( "PNG test", NULL );

    //If everything initialized fine
    return true;
}

void clean_up()
{
    //Free the surface
    SDL_FreeSurface( image );

    //Quit SDL
    SDL_Quit();
}

int main( int argc, char* args[] )
{
    //Initialize
    if( init() == false )
    {
        return 1;
    }

    //Load the image
    image = load_image( "look.png" );

    //If there was a problem in loading the image
    if( image == NULL )
    {
        return 5;
    }

    //Apply the surface to the screen
    apply_surface( 0, 0, image, screen );

    //Update the screen
    if( SDL_Flip( screen ) == -1 )
    {
        return 1;
    }

    //Wait 2 seconds
    SDL_Delay( 2000 );

    //Free the surface and quit SDL
    clean_up();


    return 0;
}

输出返回 5。

Answer 1

我的错。
我只是将 SDL_image.dll 复制到 exe floder 中。
我还应该复制 zlib1.dll 和 libpng12-0.dll
实际上，所有的dll都是需要的，因为如果没有这个dll，程序不会给出任何错误提示，这很令人困惑。

Answer 2

如果您从网站下载 libpng，您将找到一个名为 libpng12.dll 的文件。将该文件复制到 system32 中不起作用，因为 SDL_image 实际上会查找名为“libpng12-0.dll”的文件。我在代码中实现 IMG_GetError() 方法后发现了这一点。错误消息说得很清楚...

所以你要做的就是将libpng12.dll复制到system32并将其重命名为libpng12-0.dll！一切都很好。