SDL教程3——优化图像加载和显示

上一节，我们学会了如何显示一个32位位图，现在是时候开始新学习了。思考，如果我们的图片不是32位，是24位的位图，我们该如何显示？如果我们想同时显示两幅图像，一幅前景图一幅背景图，该如何操作呢？

1、加载头文件

2、定义显示面参数

3、定义加载图片函数，主要是为了方便24位图像到32位图像的转换

4、定义显示图片函数，主要是为了方便在不同位置显示图片

5、mian主函数

程序中用到两幅位图，一幅backgroud.bmp，24位，600X450分辨率；一幅hello.bmp,24位，390X295分辨率，其他解释，请参考相关代码说明，下面附上源代码：

#include "SDL.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)
{
    //Temporary storage for the image that's loaded
    SDL_Surface *loadedImage = NULL;

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

    //Load the image
    loadedImage = SDL_LoadBMP(filename.c_str());

    //If nothing went wrong in loading the image
    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("hello.bmp");
    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;
}

最后效果如图所示：

附录：

获取BMP图片小技巧：登录qq，然后打开百度图片，找到自己想要的一张图片,选择图片另存为，选择图片类型为BMP即可。如果图片太大，可用qq截图，然后同样保存为BMP图片即可！