SDL教程4——在VS2010中设置SDL扩展库

前几节我们了解到，SDL基本库只能加载普通的BMP图像，如果我们还想加载其它格式的图片，我们就需要用到SDL的扩展库，它可以帮助我们加载BMP, PNM, XPM, LBM, PCX, GIF, JPEG, TGA and PNG等格式图片。要下载SDL扩展帮助文档，点击此处！

使用扩展库之前，我们需要先从网上下载适合VS2010的库文件，点击此处，进入下载！如下图所示，下载该版本文件！

下载下来以后，同原来设置SDL基本库一样，我们设置好该扩展库的使用环境，复制dll文件至exe同目录下。

接着，我们修改上一节所写的load_image子函数，代码如下：

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;

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

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

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

    //Return the optimized image
    return optimizedImage;

}

然后我们就可以加载包括BMP之内其它格式图片。在此，我准备了两幅图片，一幅test_png.png的png格式图片：

还有一幅background.bmp的bmp格式背景图片：

完整代码如下所示：

#include "SDL.h"
#include "SDL_image.h"
#include <string>

//The  attributes of the screen
const int SCREEN_WIDTH = 600;
const int SCREEN_HEIGHT = 450;
const int SCREEN_BPP = 32;

//The surfaces that will be usede
SDL_Surface *message = NULL;
SDL_Surface *background = 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;

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

    //If the image loaded
    if(loadedImage != NULL)
    {
        //Create an optimized image
        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)
{
    //Make a temporary rectangle to hold the offsets
    SDL_Rect offset;

    //Give the offset to the rectangle
    offset.x = x;
    offset.y = y;

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

int main(int argc,char *argv[])
{
    //Initialize all SDL_subsystems
    if(SDL_Init(SDL_INIT_EVERYTHING) == -1)
    {
        return 1;
    }

    //Set up Screen
    screen = SDL_SetVideoMode(SCREEN_WIDTH,SCREEN_HEIGHT,SCREEN_BPP,SDL_SWSURFACE);
    if(screen == NULL)
    {
        return 1;
    }

    //Set the window caption
    SDL_WM_SetCaption("Hello World",NULL);

    //Load Image
    message = load_image("test_png.png");
    background = load_image("background.bmp");

    //Apply  the background  to the screen
    apply_surface(0,0,background,screen);


    //apply the message to the screen
    apply_surface(105,78,message,screen);

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

    //Wait 2 seconds
    SDL_Delay(20000);

    //Free the loaded image
    SDL_FreeSurface(message);
    SDL_FreeSurface(background);

    //Quit SDL
    SDL_Quit();

    return 0;
}

最后效果如下：