SDL(3)-键盘响应

业界资讯 2023-04-16 19:44:58 阅读次数: 0

这篇对SDL是如何响应键盘的做一个简单介介绍。

首先我们定义一个枚举，默认起始位为0，也可以显式的制定整数值。尽量养成使用符号常量的习惯，不要直接使用数字，例如if(option == 1),当我们有大量这种判断时，我们回头再来排查会相当麻烦。

enum KeyPressSurfaces
{
    KEY_PRESS_SURFACE_DEFAULT,
    KEY_PRESS_SURFACE_UP,
    KEY_PRESS_SURFACE_DOWN,
    KEY_PRESS_SURFACE_LEFT,
    KEY_PRESS_SURFACE_RIGHT,
    KEY_PRESS_SURFACE_TOTAL
};

跟之前一样，我们配置好头文件，lib文件和lib依赖项之后，我们在代码中首先定义一些变量

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

//从指定路径加载图片surface
SDL_Surface* loadSurface(std::string path);

//SDL窗口
SDL_Window* gWindow = nullptr;

//SDL窗口surface
SDL_Surface* gScreenSurface = nullptr;

//用来存储不同图片的surface, 这里的KEY_PRESS_SURFACE_TOTAL = 5
SDL_Surface* gKeyPressSurfaces[KEY_PRESS_SURFACE_TOTAL];

//当前显示的surface
SDL_Surface* gCurrentSurface = nullptr;

这里我们声明了一个函数loadSurface用来加载指定位置的图片，这样封装下可以有效降低代码量，也可以是程序看起来更清晰

SDL_Surface* loadSurface(std::string path)
{
	//加载图片
	SDL_Surface* loadSurface = SDL_LoadBMP(path.c_str());
	if (loadSurface == nullptr)
		printf("unable to load image %s!SDL_ERROR:%s\n", path.c_str(), SDL_GetError());

	return loadSurface;
}

接下来我们修改loadMedia函数，我们加载5张不同的图片，后面用来响应键盘事件

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

	//load default surface
	gKeyPressSurfaces[KEY_PRESS_SURFACE_DEFAULT] = loadSurface("../picture/press.bmp");
	if(gKeyPressSurfaces[KEY_PRESS_SURFACE_DEFAULT] == nullptr)
	{
		printf("unable to load image!SDL_ERROR%s\n", SDL_GetError());
		success = false;
	}

	gKeyPressSurfaces[KEY_PRESS_SURFACE_UP] = loadSurface("../picture/up.bmp");
	if (gKeyPressSurfaces[KEY_PRESS_SURFACE_UP] == nullptr)
	{
		printf("unable to load image!SDL_ERROR%s\n", SDL_GetError());
		success = false;
	}

	gKeyPressSurfaces[KEY_PRESS_SURFACE_DOWN] = loadSurface("../picture/down.bmp");
	if (gKeyPressSurfaces[KEY_PRESS_SURFACE_DOWN] == nullptr)
	{
		printf("unable to load image!SDL_ERROR%s\n", SDL_GetError());
		success = false;
	}

	gKeyPressSurfaces[KEY_PRESS_SURFACE_LEFT] = loadSurface("../picture/left.bmp");
	if (gKeyPressSurfaces[KEY_PRESS_SURFACE_LEFT] == nullptr)
	{
		printf("unable to load image!SDL_ERROR%s\n", SDL_GetError());
		success = false;
	}

	gKeyPressSurfaces[KEY_PRESS_SURFACE_RIGHT] = loadSurface("../picture/right.bmp");
	if (gKeyPressSurfaces[KEY_PRESS_SURFACE_RIGHT] == nullptr)
	{
		printf("unable to load image!SDL_ERROR%s\n", SDL_GetError());
		success = false;
	}

	return success;
}

接下来我们在主函数中响应键盘上的方向键来呈现不同图片

在while循环前先赋值一个显示的surface，而后在SDL事件循环中判断是否触发了按键事件，如果是，我们根据按键类型呈现不同的图片

SDL_Event e;
bool quit = false;

gCurrentSurface = gKeyPressSurfaces[KEY_PRESS_SURFACE_DEFAULT];

while (quit == false)
{
	while (SDL_PollEvent(&e) != 0)
	{
		if (e.type == SDL_QUIT)
			quit = true;

		else if (e.type == SDL_KEYDOWN)
		{
			switch (e.key.keysym.sym)
			{
			case SDLK_UP:
				gCurrentSurface = gKeyPressSurfaces[KEY_PRESS_SURFACE_UP];
				break;
			case SDLK_DOWN:
				gCurrentSurface = gKeyPressSurfaces[KEY_PRESS_SURFACE_DOWN];
				break;
			case SDLK_LEFT:
				gCurrentSurface = gKeyPressSurfaces[KEY_PRESS_SURFACE_LEFT];
				break;
			case SDLK_RIGHT:
				gCurrentSurface = gKeyPressSurfaces[KEY_PRESS_SURFACE_RIGHT];
				break;

			default:
				gCurrentSurface = gKeyPressSurfaces[KEY_PRESS_SURFACE_DEFAULT];
				break;
			}
		}
	}


    //这里我们先把背景色填充下，不然背景会不断叠加
	SDL_FillRect(gScreenSurface, nullptr, SDL_MapRGB(gScreenSurface->format, 0xff, 0xfd, 0xdd));

	//拷贝到窗口的surface
	SDL_BlitSurface(gCurrentSurface, nullptr, gScreenSurface, nullptr);

	//更新窗口
	SDL_UpdateWindowSurface(gWindow);
}

最后关闭程序前，别忘了释放内存空间

for (int i = 0; i < KEY_PRESS_SURFACE_TOTAL; ++i)
	{
		SDL_FreeSurface(gKeyPressSurfaces[i]);
		gKeyPressSurfaces[i] = NULL;
	}

	SDL_FreeSurface(gScreenSurface);
	gScreenSurface = nullptr;

以下是运行效果

完整代码如下

#include <iostream>
#include <sdl.h>

//key press surface constants
enum KeyPressSurfaces
{
	KEY_PRESS_SURFACE_DEFAULT,
	KEY_PRESS_SURFACE_UP,
	KEY_PRESS_SURFACE_DOWN,
	KEY_PRESS_SURFACE_LEFT,
	KEY_PRESS_SURFACE_RIGHT,
	KEY_PRESS_SURFACE_TOTAL,

};


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* gKeyPressSurfaces[KEY_PRESS_SURFACE_TOTAL];

SDL_Surface* gCurrentSurface = nullptr;


SDL_Surface* loadSurface(std::string path)
{
	//load image at secified path
	SDL_Surface* loadSurface = SDL_LoadBMP(path.c_str());
	if (loadSurface == nullptr)
		printf("unable to load image %s!SDL_ERROR:%s\n", path.c_str(), SDL_GetError());

	return loadSurface;

}

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("deal key press", 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 default surface
	gKeyPressSurfaces[KEY_PRESS_SURFACE_DEFAULT] = loadSurface("../picture/press.bmp");
	if(gKeyPressSurfaces[KEY_PRESS_SURFACE_DEFAULT] == nullptr)
	{
		printf("unable to load image!SDL_ERROR%s\n", SDL_GetError());
		success = false;
	}

	gKeyPressSurfaces[KEY_PRESS_SURFACE_UP] = loadSurface("../picture/up.bmp");
	if (gKeyPressSurfaces[KEY_PRESS_SURFACE_UP] == nullptr)
	{
		printf("unable to load image!SDL_ERROR%s\n", SDL_GetError());
		success = false;
	}

	gKeyPressSurfaces[KEY_PRESS_SURFACE_DOWN] = loadSurface("../picture/down.bmp");
	if (gKeyPressSurfaces[KEY_PRESS_SURFACE_DOWN] == nullptr)
	{
		printf("unable to load image!SDL_ERROR%s\n", SDL_GetError());
		success = false;
	}

	gKeyPressSurfaces[KEY_PRESS_SURFACE_LEFT] = loadSurface("../picture/left.bmp");
	if (gKeyPressSurfaces[KEY_PRESS_SURFACE_LEFT] == nullptr)
	{
		printf("unable to load image!SDL_ERROR%s\n", SDL_GetError());
		success = false;
	}

	gKeyPressSurfaces[KEY_PRESS_SURFACE_RIGHT] = loadSurface("../picture/right.bmp");
	if (gKeyPressSurfaces[KEY_PRESS_SURFACE_RIGHT] == nullptr)
	{
		printf("unable to load image!SDL_ERROR%s\n", SDL_GetError());
		success = false;
	}

	return success;
}


void close()
{
	for (int i = 0; i < KEY_PRESS_SURFACE_TOTAL; ++i)
	{
		SDL_FreeSurface(gKeyPressSurfaces[i]);
		gKeyPressSurfaces[i] = NULL;
	}

	SDL_FreeSurface(gScreenSurface);
	gScreenSurface = nullptr;

	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;

			gCurrentSurface = gKeyPressSurfaces[KEY_PRESS_SURFACE_DEFAULT];

			while (quit == false)
			{
				while (SDL_PollEvent(&e) != 0)
				{
					if (e.type == SDL_QUIT)
						quit = true;

					else if (e.type == SDL_KEYDOWN)
					{
						switch (e.key.keysym.sym)
						{
						case SDLK_UP:
							gCurrentSurface = gKeyPressSurfaces[KEY_PRESS_SURFACE_UP];
							break;
						case SDLK_DOWN:
							gCurrentSurface = gKeyPressSurfaces[KEY_PRESS_SURFACE_DOWN];
							break;
						case SDLK_LEFT:
							gCurrentSurface = gKeyPressSurfaces[KEY_PRESS_SURFACE_LEFT];
							break;
						case SDLK_RIGHT:
							gCurrentSurface = gKeyPressSurfaces[KEY_PRESS_SURFACE_RIGHT];
							break;
						/*default:
							gCurrentSurface = gKeyPressSurfaces[KEY_PRESS_SURFACE_DEFAULT];
							break;*/
						}
					}
				} 


				SDL_FillRect(gScreenSurface, nullptr, SDL_MapRGB(gScreenSurface->format, 0xff, 0xfd, 0xdd));


				//apply the current image
				SDL_BlitSurface(gCurrentSurface, nullptr, gScreenSurface, nullptr);

				//update the surface
				SDL_UpdateWindowSurface(gWindow);
				

			}
		}


	}

	close();
	return 0;
}

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转载自blog.csdn.net/yunxiaobaobei/article/details/130187496
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