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 title
SDL_WINDOWPOS_UNDEFINED, // initial x position
SDL_WINDOWPOS_UNDEFINED, // initial y position
640, // width, in pixels
480, // height, in pixels
SDL_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 pointer
SDL_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 title
SDL_WINDOWPOS_UNDEFINED, // initial x position
SDL_WINDOWPOS_UNDEFINED, // initial y position
640, // width, in pixels
480, // height, in pixels
SDL_WINDOW_SHOWN | SDL_WINDOW_BORDERLESS// flags - see below
);
// Check that the window was successfully created
if (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 renderer
if (renderer)
SDL_DestroyRenderer(renderer);
// Close and destroy the window
if (window)
SDL_DestroyWindow(window);
// Clean up
SDL_Quit();
return 0;
}