SDL Lib笔记 （一） 基本框架

如果有一套跨平台的框架程序能够不用在OS的API之间折腾，或者类似GLUT略坑。。

SDL就是这个答案，最早在StuntRally里面就看到过使用这个库作为框架窗口，里面的窗口分割，用户输入等也是基于SDL来做的。

一边看Lazy Foo的tutorial，一边感叹写的真是非常贴心，比N这样的无私分享奉献太可贵了，想起了很老的NEHE教程。。

框架无非就是初始化——加载资源——渲染（事件监听）——释放资源——结束这几个过程

采用SDL_Image lib，加载一幅JPEG图片，填满窗口作为渲染内容

当前三国杀新出的界限突破武将——界限突破许褚

做一些笔记过程

/*This source code copyrighted by Lazy Foo' Productions (2004-2013)
and may not be redistributed without written permission.*/

//Using SDL, SDL_image, standard IO, and strings
#include <SDL.h>
#include <SDL_image.h>
#include <stdio.h>
#include <string>

//Screen dimension constants
const int SCREEN_WIDTH = 640;
const int SCREEN_HEIGHT = 480;

//Starts up SDL and creates window
bool init();

//Loads media
bool loadMedia();

//Frees media and shuts down SDL
void close();

//Loads individual image
SDL_Surface* loadSurface( std::string path );

//The window we'll be rendering to
SDL_Window* gWindow = NULL;

//The surface contained by the window
SDL_Surface* gScreenSurface = NULL;

//Current displayed PNG image
SDL_Surface* gPNGSurface = NULL;

bool init()
{
	//Initialization flag
	bool success = true;

	//Initialize SDL
	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 == NULL )
		{
			printf( "Window could not be created! SDL Error: %s\n", SDL_GetError() );
			success = false;
		}
		else
		{
			//Initialize Image loading
			int imgFlags = IMG_INIT_JPG;
			if( !( IMG_Init( imgFlags ) & imgFlags ) )
			{
				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;
}

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

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

	return success;
}

void close()
{
	//Free loaded image
	SDL_FreeSurface( gPNGSurface );
	gPNGSurface = NULL;

	//Destroy window
	SDL_DestroyWindow( gWindow );
	gWindow = NULL;

	//Quit SDL subsystems
	IMG_Quit();
	SDL_Quit();
}

SDL_Surface* loadSurface( std::string path )
{
	//The final optimized image
	SDL_Surface* optimizedSurface = NULL;

	//Load image at specified path
	SDL_Surface* loadedSurface = IMG_Load( path.c_str() );
	if( loadedSurface == NULL )
	{
		printf( "Unable to load image %s! SDL_image Error: %s\n", path.c_str(), IMG_GetError() );
	}
	else
	{
		//Convert surface to screen format
		optimizedSurface = SDL_ConvertSurface( loadedSurface, gScreenSurface->format, NULL );
		if( optimizedSurface == NULL )
		{
			printf( "Unable to optimize image %s! SDL Error: %s\n", path.c_str(), SDL_GetError() );
		}


		//Get rid of old loaded surface
		SDL_FreeSurface( loadedSurface );
	}

	return optimizedSurface;
}

int main( int argc, char* args[] )
{
	//Start up SDL and create window
	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
			//Apply the image stretched
			SDL_Rect stretchRect;
			stretchRect.x = 0;
			stretchRect.y = 0;
			stretchRect.w = SCREEN_WIDTH;
			stretchRect.h = SCREEN_HEIGHT;
			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 to the window size
				SDL_BlitScaled( gPNGSurface, NULL, gScreenSurface, &stretchRect );

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

	//Free resources and close SDL
	close();

	return 0;
}

主要的API

SDL_Init 初始化

SDL_CreateWindow 创建渲染窗口，指定窗口大小

IMG_Init 初始化图像文件读取函数，需要指定图像文件类型如PNG JPG等

SDL_GetWindowSurface 获取Window的SDL_Surface* 类型

SDL_FreeSurface 释放Surface资源

SDL_PollEvent 处理事件队列里的事件，没有事件的时候返回0

SDL_BlitScaled 和下面的函数都是将surface内容copy到另外一个surface，这个新版本可以指定copy以后的大小，比如用于填充窗口

SDL_BlitSurface

SDL_UpdateWindowSurface 刷新当前显示，更新双缓冲前后页面

IMG_Quit(); 退出对应的函数库
SDL_Quit();