时钟的SDL2实现示例

基本实现思路是这样：有一个表盘图片和三个指针图片，表盘图片作为背景，指针图片起始点在表盘的中央。获取系统时间，计算指针角度，重绘。监听退出事件，程序退出。

实现效果如下：

具体代码：

#include "SDL2/SDL.h"
#include
#include

const int SCREEN_;
const int SCREEN_;

SDL_Window *window = NULL;
SDL_Renderer *renderer = NULL;

/* print out error information */
void ShowError() {
 printf("%sn", SDL_GetError());
}

/* load image by filename */
SDL_Texture* LoadImage(char file[]) {
 SDL_Surface *loadedImage = NULL;
 SDL_Texture *texture = NULL;

 loadedImage = SDL_LoadBMP(file);
 if (loadedImage != NULL) {
  texture = SDL_CreateTextureFromSurface(renderer, loadedImage);
  SDL_FreeSurface(loadedImage);
 }
 else
  ShowError();
 return texture;
}

/* show the backgroud */
void ApplyBackground(SDL_Texture *tex, SDL_Renderer *rend) {
 SDL_Rect pos;
 SDL_QueryTexture(tex, NULL, NULL, &pos.w, &pos.h);
 pos.x = pos.y = 0;
 SDL_RenderCopy(renderer, tex, NULL, NULL);
}

/* show the pointers by angle */
void ApplySurface(SDL_Texture *tex, SDL_Renderer *rend, double angle) {
 int x = SCREEN_WIDTH/2+7;
 int y = SCREEN_HEIGHT/2;
 
 SDL_RendererFlip flip = SDL_FLIP_HORIZONTAL | SDL_FLIP_VERTICAL;
 SDL_Rect pos;
 SDL_QueryTexture(tex, NULL, NULL, &pos.w, &pos.h);
 
 pos.x = x;
 pos.y = y;
 SDL_Point p = {0, 0};
 SDL_RenderCopyEx(renderer, tex, NULL, &pos, angle, &p, flip);
}

int main() {
 if (SDL_Init(SDL_INIT_EVERYTHING) == -1) {
  ShowError();
  return 1;
 }
 
 /* Initial Window */
 window = SDL_CreateWindow("Clock", SDL_WINDOWPOS_CENTERED,
  SDL_WINDOWPOS_CENTERED, SCREEN_WIDTH, SCREEN_HEIGHT, SDL_WINDOW_SHOWN);
 if (window == NULL) {
  ShowError();
  return 2;
 }
 
 /* Initial Renderer */
 renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC);
 if (renderer == NULL) {
  ShowError();
  return 3;
 }
 
 /* load pictures */
 SDL_Texture *background = NULL, *hour = NULL,
    *min = NULL, *second = NULL;
 background = LoadImage("background.bmp");
 hour = LoadImage("hour.bmp");
 min = LoadImage("min.bmp");
 second = LoadImage("second.bmp");

 if (background == NULL | hour == NULL | min == NULL | second == NULL) {
  return 4;
 }

 time_t rawtime;
 struct tm *timeinfo;
 int quit = 0;
 SDL_Event e;
 
 /* begin to run */
 while (!quit) {
  time(&rawtime);
  timeinfo = localtime(&rawtime);
  
  /* get system time */
  int h = timeinfo->tm_hour % 12, m = timeinfo->tm_min,
   s = timeinfo->tm_sec;
  
  /* calculate their angles */
  double angle_s = s*1.0*6 - 90;
  double angle_m = m*1.0*6 + angle_s/360*6 - 90;
  double angle_h = h*1.0*30 + angle_m/360/2 - 90;
  
  /* repaint */
  SDL_RenderClear(renderer);
  ApplyBackground(background, renderer);
  ApplySurface(hour, renderer, angle_h);
  ApplySurface(min, renderer, angle_m);
  ApplySurface(second, renderer, angle_s);

  SDL_RenderPresent(renderer);
  SDL_Delay(1000);
  
  /* way to quit */
  while (SDL_PollEvent(&e)) {
   if (e.type == SDL_QUIT) // close the window
    quit = 1;
   if (e.type == SDL_MOUSEBUTTONDOWN) // click the mouse
    quit = 1;
  }
 }
 /* Free Memory */
 SDL_DestroyTexture(background);
 SDL_DestroyTexture(hour);
 SDL_DestroyTexture(min);
 SDL_DestroyTexture(second);
 SDL_DestroyRenderer(renderer);
 SDL_DestroyWindow(window);

 SDL_Quit();
 
 return 0;
}