SDL(2)-加载图片

加载BMP

1.使用SDL_init初始化SDL库

2.使用SDL_CreateWindow创建一个窗口

3.使用SDL_GetWindowSurface获取创建窗口的surface

4.使用SDL_LoadBMP加载一张BMP图片

5.使用SDL_BlitSurface将加载的bmp surface拷贝到窗口的surface

6.使用SDL_UpdateWindowSurface更新到窗口

7.使用SDL_FreeSurface释放申请的空间

8.使用SDL_DestroyWindow销毁窗口

9.使用SDL_Quit释放SDL库

以下时完整代码

#include 
#include 

const int SCREEN_WIDTH = 640;
const int  SCREEN_HEIGHT = 480;

SDL_Window* gWindow = nullptr;
SDL_Surface* gScreenSurface = nullptr;
SDL_Surface* gHelloWorld = nullptr;

bool init()
{
	bool success = true;

	if (SDL_Init(SDL_INIT_VIDEO) < 0)
	{
		printf("SDL could not initialize!SDL Error:%s\n", SDL_GetError());
		success = false;
	}
	else
	{
		//create window
		gWindow = SDL_CreateWindow("SDL tutorial", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, SCREEN_WIDTH, SCREEN_HEIGHT, SDL_WINDOW_SHOWN);
		if (gWindow == nullptr)
		{
			printf("window could not created!SDL_Error:%s\n", SDL_GetError());
			success = false;
		}
		else
		{
			//get window surface
			gScreenSurface = SDL_GetWindowSurface(gWindow);

		}

	}

	return success;
}


bool loadMedia()
{
	//loading success flag
	bool success = true;

	//load splash image
	gHelloWorld = SDL_LoadBMP("../BMP2.bmp");
	if (gWindow == nullptr)
	{
		printf("unable to load image!SDL_ERROR%s\n",SDL_GetError());
		success = false;
	}

	return success;
}


void close()
{
	SDL_FreeSurface(gHelloWorld);
	gHelloWorld = NULL;

	SDL_DestroyWindow(gWindow);
	gWindow = NULL;

	SDL_Quit();

}


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

	if (!init())
	{
		printf("failed to initialize!\n");
	}
	else
	{
		//load media
		if (!loadMedia())
		{
			printf("failed to load media!\n");
		}
		else
		{
			SDL_BlitSurface(gHelloWorld, nullptr, gScreenSurface, nullptr);

			//update the surface
			SDL_UpdateWindowSurface(gWindow);

			SDL_Event e;
			bool quit = false;

			while (quit == false)
			{
				while (SDL_PollEvent(&e))
				{
					if (e.type == SDL_QUIT)
						quit = true;
				}
			}
		}


	}

	close();
	return 0;
}

加载PNG

由于默认的SDL库只能加载BMP格式的图片，如果需要加载png等其他格式的图片，需要下载一个扩展库SDL_image​​​​​​

这里我们下载SDL2_image-devel-2.6.3-VC.zipSDL_image​​​​​​

 加载步骤与加载BMP步骤差不多，这里需要注意以下几点

1.需要使用IMG_Init初始化iamge库

2. 使用IMG_Load加载png图片（之前使用SDL_LoadBMP加载BMP）

3.使用IMG_Quit释放image库

以下是完整代码

#include 
#include 
#include 
#include 

using namespace std;

const int SCREEN_WIDTH = 640;
const int  SCREEN_HEIGHT = 480;


SDL_Surface* loadSurface(std::string path);

SDL_Window* gWindow = nullptr;

SDL_Surface* gScreenSurface = nullptr;

SDL_Surface* gPNGSurface = nullptr;


bool init()
{
    bool success = true;
    //initialize SDL
    if (SDL_Init(SDL_INIT_VIDEO) < 0)
    {
        printf("SDL_ERROR:%s\n", SDL_GetError());
        success = false;
    }
    else
    {
        //create window
        gWindow = SDL_CreateWindow("SDL load PNG", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, SCREEN_WIDTH, SCREEN_HEIGHT, SDL_WINDOW_SHOWN );
        if (gWindow == nullptr)
        {
            printf("SDL_ERROR:%s\n", SDL_GetError());
            success = false;

        }
        else
        {
            //initialize PNG loading
            int imgFlag = IMG_INIT_PNG;

            if (!(IMG_Init(imgFlag) & imgFlag))
            {
                printf("SDL_IMAGE could not initialize!SDL_IMAGE ERROR: %s\n", IMG_GetError());
                success = false;
            }
            else
            {
                //get window surface
                gScreenSurface = SDL_GetWindowSurface(gWindow);
            }
        }
        
    }

    return success;
}


SDL_Surface* loadSurface(string path)
{
    SDL_Surface* optimizedSurface = nullptr;

    //load image at specified path
    SDL_Surface* loadSurface = IMG_Load(path.c_str());
    if (loadSurface == nullptr)
    {
        printf("load image error: %s\n", IMG_GetError());
    }
    else
    {
        //convert surface to screen format
        optimizedSurface = SDL_ConvertSurface(loadSurface, gScreenSurface->format, 0);
        if (optimizedSurface == nullptr)
        {
            printf("unable to optimize image: %s\n", SDL_GetError());
        }

        //get rid of old loaded surface
        SDL_FreeSurface(loadSurface);
    }

    return optimizedSurface;
}

bool loadMedia()
{
    //Loading success flag
    bool success = true;

    //Load PNG surface
    gPNGSurface = loadSurface("../picture/loaded.png");
    if (gPNGSurface == NULL)
    {
        printf("Failed to load PNG image!\n");
        success = false;
    }

    return success;
}

void close()
{
    SDL_FreeSurface(gPNGSurface);
    gPNGSurface = nullptr;

    SDL_DestroyWindow(gWindow);
    gWindow = nullptr;

    IMG_Quit();
    SDL_Quit();
}


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

    if (!init())
    {
        printf("Failed to initialize!\n");
    }
    else
    {
        //Load media
        if (!loadMedia())
        {
            printf("Failed to load media!\n");
        }
        else
        {
            //Main loop flag
            bool quit = false;

            //Event handler
            SDL_Event e;

            //While application is running
            while (!quit)
            {
                //Handle events on queue
                while (SDL_PollEvent(&e) != 0)
                {
                    //User requests quit
                    if (e.type == SDL_QUIT)
                    {
                        quit = true;
                    }
                }

                //Apply the PNG image
                SDL_BlitSurface(gPNGSurface, NULL, gScreenSurface, NULL);

                //Update the surface
                SDL_UpdateWindowSurface(gWindow);
            }
        }
    }

    //Free resources and close SDL
    close();

    return 0;
}