【音视频】SDL事件

SDL 事件

函数

SDL_WaitEvent()： 等待一个事件
SDL_PushEvent()： 发送一个事件
SDL_PumpEvents()：将硬件设备产生的事件放入事件队列，用于读取事件，在调用该函数之前，必须调用SDL_PumpEvents搜集键盘等事件
SDL_PeepEvents()： 从事件队列提取一个事件

数据结构

SDL_Event： 代表一个事件

实现流程

创建窗口

创建一个窗口，标题为An SDL2 window，其中后面两个参数的意义如下：

SDL_WINDOW_SHOWN：窗口创建后立即显示。
SDL_WINDOW_BORDERLESS：去除窗口边框，实现无边框效果

SDL_Window *window = NULL;  
window = SDL_CreateWindow("An SDL2 window",                  // window titleSDL_WINDOWPOS_UNDEFINED,           // initial x positionSDL_WINDOWPOS_UNDEFINED,           // initial y position640,                               // width, in pixels480,                               // height, in pixelsSDL_WINDOW_SHOWN | SDL_WINDOW_BORDERLESS// flags - see below);

创建渲染器

创建一个渲染器，用于窗口的渲染

SDL_Renderer *renderer = NULL;
renderer = SDL_CreateRenderer(window, -1, 0);

渲染初始帧

因为只需要一帧就好，因此我们直接在循环外进行初始帧的渲染即可，相关API的意义如下

SDL_SetRenderDrawColor：设置渲染颜色（此处为红色）。
SDL_RenderClear：用指定颜色清空渲染目标（即窗口背景）。
SDL_RenderPresent：将渲染结果提交到窗口显示

/* We must call SDL_CreateRenderer in order for draw calls to affect this window. */
renderer = SDL_CreateRenderer(window, -1, 0);/* Select the color for drawing. It is set to red here. */
SDL_SetRenderDrawColor(renderer, 255, 0, 0, 255);/* Clear the entire screen to our selected color. */
SDL_RenderClear(renderer);/* Up until now everything was drawn behind the scenes.This will show the new, red contents of the window. */
SDL_RenderPresent(renderer);

设置事件循环

开始事件循环，根据不同的输入处理不同事件：

事件循环机制

SDL_WaitEvent：阻塞等待事件触发，适用于单线程事件处理
所有事件（如键盘、鼠标、自定义事件）均存储在队列中，按顺序处理

键盘事件

处理键盘按下的操作
当按下q的时候向事件队列中加入自定义的退出事件，这个事件类型需要在这个SDL_USEREVENT的基础上进行累加，比如

#define FF_QUIT_EVENT    (SDL_USEREVENT + 2) // 用户自定义事件

加入自定义事件

SDL_Event event_q;
event_q.type = FF_QUIT_EVENT;
SDL_PushEvent(&event_q);

鼠标按下事件

处理鼠标左键按下/右键按下/其他键（滚轮键按下等）

鼠标移动事件

获取鼠标移动时的坐标

自定义事件

FF_QUIT_EVENT事件是我们自定义的事件，需要使用SDL的宏SDL_USEREVENT的基础上进行累加，比如

#define FF_QUIT_EVENT    (SDL_USEREVENT + 2) // 用户自定义事件

处理自定义事件

case FF_QUIT_EVENT:printf("receive quit event\n");b_exit = 1;break;
}
if(b_exit)break;

SDL_Event event;
int b_exit = 0;
for (;;)
{SDL_WaitEvent(&event);switch (event.type){case SDL_KEYDOWN:	/* 键盘事件 */switch (event.key.keysym.sym){case SDLK_a:printf("key down a\n");break;case SDLK_s:printf("key down s\n");break;case SDLK_d:printf("key down d\n");break;case SDLK_q:printf("key down q and push quit event\n");SDL_Event event_q;event_q.type = FF_QUIT_EVENT;SDL_PushEvent(&event_q);break;default:printf("key down 0x%x\n", event.key.keysym.sym);break;}break;case SDL_MOUSEBUTTONDOWN:			/* 鼠标按下事件 */if (event.button.button == SDL_BUTTON_LEFT){printf("mouse down left\n");}else if(event.button.button == SDL_BUTTON_RIGHT){printf("mouse down right\n");}else{printf("mouse down %d\n", event.button.button);}break;case SDL_MOUSEMOTION:		/* 鼠标移动事件 */printf("mouse movie (%d,%d)\n", event.button.x, event.button.y);break;case FF_QUIT_EVENT:printf("receive quit event\n");b_exit = 1;break;}if(b_exit)break;
}

完整代码

main.c

#include <SDL.h>
#include <stdio.h>
#define FF_QUIT_EVENT    (SDL_USEREVENT + 2) // 用户自定义事件
#undef main
int main(int argc, char* argv[])
{SDL_Window *window = NULL;              // Declare a pointerSDL_Renderer *renderer = NULL;SDL_Init(SDL_INIT_VIDEO);               // Initialize SDL2// Create an application window with the following settings:window = SDL_CreateWindow("An SDL2 window",                  // window titleSDL_WINDOWPOS_UNDEFINED,           // initial x positionSDL_WINDOWPOS_UNDEFINED,           // initial y position640,                               // width, in pixels480,                               // height, in pixelsSDL_WINDOW_SHOWN | SDL_WINDOW_BORDERLESS// flags - see below);// Check that the window was successfully createdif (window == NULL){// In the case that the window could not be made...printf("Could not create window: %s\n", SDL_GetError());return 1;}/* We must call SDL_CreateRenderer in order for draw calls to affect this window. */renderer = SDL_CreateRenderer(window, -1, 0);/* Select the color for drawing. It is set to red here. */SDL_SetRenderDrawColor(renderer, 255, 0, 0, 255);/* Clear the entire screen to our selected color. */SDL_RenderClear(renderer);/* Up until now everything was drawn behind the scenes.This will show the new, red contents of the window. */SDL_RenderPresent(renderer);SDL_Event event;int b_exit = 0;for (;;){SDL_WaitEvent(&event);switch (event.type){case SDL_KEYDOWN:	/* 键盘事件 */switch (event.key.keysym.sym){case SDLK_a:printf("key down a\n");break;case SDLK_s:printf("key down s\n");break;case SDLK_d:printf("key down d\n");break;case SDLK_q:printf("key down q and push quit event\n");SDL_Event event_q;event_q.type = FF_QUIT_EVENT;SDL_PushEvent(&event_q);break;default:printf("key down 0x%x\n", event.key.keysym.sym);break;}break;case SDL_MOUSEBUTTONDOWN:			/* 鼠标按下事件 */if (event.button.button == SDL_BUTTON_LEFT){printf("mouse down left\n");}else if(event.button.button == SDL_BUTTON_RIGHT){printf("mouse down right\n");}else{printf("mouse down %d\n", event.button.button);}break;case SDL_MOUSEMOTION:		/* 鼠标移动事件 */printf("mouse movie (%d,%d)\n", event.button.x, event.button.y);break;case FF_QUIT_EVENT:printf("receive quit event\n");b_exit = 1;break;}if(b_exit)break;}//destory rendererif (renderer)SDL_DestroyRenderer(renderer);// Close and destroy the windowif (window)SDL_DestroyWindow(window);// Clean upSDL_Quit();return 0;
}