简单的时钟，示例 SDL2 的普通颜色板纹理、自定义事件、定时器

// Time.c
// SDL2 时钟：自定义消息与计时器
// gcc -mwindows -o Time Time.c -lSDL2 -lSDL2main -lSDL2_ttf
// C4droid

//#define _DEBUG_

#include <stdio.h>
#include <string.h>
#include <time.h>
#include <SDL2/SDL.h>
#include <SDL2/SDL_ttf.h>

// 字符串常量
char szWindowTitle[] = "SDL2 时钟";
char *szWeekCN[7] = {"天", "一", "二", "三", "四",  "五",  "六"};      // 星期汉字
char szTimeFormat[]  = "%d年%02d月%02d日 星期%s %02d点%02d分%02d秒";    // 时钟格式
char *szFontFile[2]  = {"/system/fonts/DroidSansFallback.ttf",          // 安卓系统中字体文件
"C:/Windows/Fonts/msyh.ttf"};                   // Windows系统中字体文件

Uint32 TimerFunc(Uint32 nInterval, void *param);
SDL_Texture *GetColorTexture(SDL_Renderer *pRenderer, int nWidth, int nHeight, int color);
SDL_Texture *GetStringTexture(SDL_Renderer *pRenderer, char *szString, TTF_Font *pFont, int color);
void PrintString(SDL_Renderer *pRenderer, SDL_Rect *prt, char *szString, TTF_Font *pFont, int color);

#undef main
int main(int argc, char *argv[])
{
int nWindowWidth, nWindowHeight;    // 窗口尺寸
SDL_Window   *pWindow      = NULL;  // 窗口
SDL_Renderer *pRenderer    = NULL;  // 渲染器
SDL_Texture  *pBackTexture = NULL;  // 背景纹理
SDL_Texture  *pTextTexture = NULL;  // 文字纹理
TTF_Font     *pFont        = NULL;  // 文字字体
SDL_Rect     rt;                    // 文字位置
SDL_TimerID  iTimeID;       // 定时器ID
Uint32    SDL_MyTimerEvent; // 自定义事件类型ID
Uint32    nInterval = 1000; // 定时间隔
SDL_Event event;
_Bool     bRun = 1;
char      szMsg[256];
time_t    nRawTime;
struct tm *pt;

// 初始化
if(SDL_Init(SDL_INIT_EVERYTHING) == -1 || TTF_Init() == -1)
{
#ifdef _DEBUG_
fprintf(stderr, "1 %s", SDL_GetError());
#endif
goto label_error;
}
// 创建主窗口及其渲染器、背景板
if(SDL_CreateWindowAndRenderer(0, 0, SDL_WINDOW_FULLSCREEN, &pWindow, &pRenderer) == -1)
{
#ifdef _DEBUG_
fprintf(stderr, "2 %s", SDL_GetError());
#endif
goto label_error;
}
SDL_SetWindowTitle(pWindow, szWindowTitle);
SDL_GetWindowSize(pWindow, &nWindowWidth, &nWindowHeight);
rt.x = 0;
rt.y = nWindowHeight/2-20;
rt.w = nWindowWidth;
rt.h = 40;
if(NULL == (pBackTexture = GetColorTexture(pRenderer, nWindowWidth, nWindowHeight, 0xFFFF)))
{
#ifdef _DEBUG_
fprintf(stderr, "3 %s", SDL_GetError());
#endif
goto label_error;
}
// 加载字体文件
if(strcmp(SDL_GetPlatform(), "Android") == 0)
pFont = TTF_OpenFont(szFontFile[0], 20);
else if(strcmp(SDL_GetPlatform(), "Windows") == 0)
pFont = TTF_OpenFont(szFontFile[1], 20);
if(NULL == pFont)
{
#ifdef _DEBUG_
fprintf(stderr, "4 %s", SDL_GetError());
#endif
goto label_error;
}

// 取得定义定时器触发的事件类型号
if((SDL_MyTimerEvent = SDL_RegisterEvents(1)) == -1)
{
#ifdef _DEBUG_
fprintf(stderr, "5 %s", SDL_GetError());
#endif
goto label_error;
}
// 启动定时器
if((iTimeID = SDL_AddTimer(nInterval, TimerFunc, &SDL_MyTimerEvent)) == 0)
{
#ifdef _DEBUG_
fprintf(stderr, "6 %s", SDL_GetError());
#endif
goto label_error;
}

while(bRun && SDL_WaitEvent(&event))
{
switch (event.type)
{
case SDL_USEREVENT :
if(event.type == SDL_MyTimerEvent)
{
time(&nRawTime);
pt = localtime(&nRawTime);
sprintf(szMsg, szTimeFormat, pt->tm_year+1900, pt->tm_mon+1, pt->tm_mday,
szWeekCN[pt->tm_wday], pt->tm_hour, pt->tm_min, pt->tm_sec);

SDL_RenderClear(pRenderer);
SDL_RenderCopyEx(pRenderer, pBackTexture, NULL, NULL, 0, NULL, SDL_FLIP_NONE);
PrintString(pRenderer, &rt, szMsg, pFont, 0);
SDL_RenderPresent(pRenderer);
}
break;

case SDL_QUIT :
bRun = 0;
break;
}
}

// 异常退出
label_error:
if(pRenderer != NULL)   SDL_DestroyRenderer(pRenderer);
if(pWindow != NULL)     SDL_DestroyWindow(pWindow);
if(pFont != NULL)       TTF_CloseFont(pFont);
TTF_Quit();
SDL_Quit();
return 0;
}

// 显示文字时钟
// 参数：pRenderer = 渲染器；prt = 显示文字的位置；szString = 文字内容；pFont = 字体；pColor = 文字颜色
void PrintString(SDL_Renderer *pRenderer, SDL_Rect *prt, char *szString, TTF_Font *pFont, int color)
{
SDL_Texture *pTextTexture;

if((pTextTexture = GetStringTexture(pRenderer, szString, pFont, color)) != NULL)
{
SDL_RenderCopyEx(pRenderer, pTextTexture, NULL, prt, 0, NULL, SDL_FLIP_NONE);
SDL_DestroyTexture(pTextTexture);
}
}

// 定时器处理过程
// 参数：nInterval = 定时间隔；param = 参数（这里给的是自定义事件类型ID）
Uint32 TimerFunc(Uint32 nInterval, void *param)
{
SDL_Event event;

SDL_zero(event);
event.type = *((Uint32 *)param);
SDL_PushEvent(&event);

return nInterval;
}

// 取得字符串纹理
// 参数：pRenderer = 渲染器；szString = 字符串内容；pFont = 字体；color = 文字颜色
// 返回值：纹理指针
SDL_Texture *GetStringTexture(SDL_Renderer *pRenderer, char *szString, TTF_Font *pFont, int color)
{
SDL_Texture *pTexture;
SDL_Surface *pSurface;
SDL_Color c = {color>>16, (color>>8)&0xFF, color&0xFF};

if((pSurface = TTF_RenderUTF8_Blended(pFont, szString, c)) == NULL)
return NULL;
pTexture = SDL_CreateTextureFromSurface(pRenderer, pSurface);
SDL_FreeSurface(pSurface);

return pTexture;
}

// 取得颜色板纹理
// 参数：pRenderer = 渲染器；nWidth，nHeight = 颜色板尺寸；color = 颜色
// 返回值：纹理指针
SDL_Texture *GetColorTexture(SDL_Renderer *pRenderer, int nWidth, int nHeight, int color)
{
SDL_Texture *pTexture;
SDL_Surface *pSurface;

if((pSurface = SDL_CreateRGBSurface(0, nWidth, nHeight, 32, 0, 0, 0, 0)) == NULL)
return NULL;
SDL_FillRect(pSurface, NULL, color);
pTexture = SDL_CreateTextureFromSurface(pRenderer, pSurface);
SDL_FreeSurface(pSurface);

return pTexture;
}