//srcRect為視頻區(qū)域，angle為旋轉角度
const double PI = 3.1415926535897935384626;
//角度轉弧度，用于三角函數(shù)計算。
double theta = PI / 180.0 * angle;
//計算旋轉后的邊框大小，+0.5四舍五入
int width = srcRect->h * fabs(sin(theta) )+ srcRect->w * fabs(cos(theta)) + 0.5;
int height = srcRect->h * fabs(cos(theta)) + srcRect->w * fabs(sin(theta)) + 0.5;

//邊框的寬高比
double srcBorderRatio = (double)width / height;
//目標區(qū)域的寬高比
double dstRatio = (double)dstRect->w / dstRect->h;
//計算邊框縮放到目標區(qū)域的大小
int zoomWidth;
int zoomHeight;
if (srcBorderRatio > dstRatio)
{
	zoomWidth = dstRect->w;
	zoomHeight = dstRect->w / srcBorderRatio;
}
else
{
	zoomWidth = dstRect->h * srcBorderRatio;
	zoomHeight = dstRect->h;
}

//視頻的寬高比
double srcRatio = (double)srcRect->w / srcRect->h;
//通過縮放后的邊框計算還原的圖像大小
targetRect.h = (double)zoomWidth / (fabs(sin(theta) )+ srcRatio * fabs(cos(theta)));
targetRect.w = targetRect.h * srcRatio;
targetRect.x = (dstRect->w- targetRect.w ) / 2;
targetRect.y = (dstRect->h- targetRect.h ) / 2;

/// <summary>
/// 計算旋轉的矩形大小
/// </summary>
/// <param name="src">原圖像區(qū)域</param>
/// <param name="dst">目標區(qū)域</param>
/// <param name="angle">旋轉角度</param>
/// <returns></returns>
static SDL_Rect getRotateRect(SDL_Rect *srcRect, SDL_Rect* dstRect,double angle) {
	SDL_Rect targetRect;
	const double PI = 3.1415926535897935384626;
	double theta = PI / 180.0 * angle;
	//計算旋轉后的邊框大小
	int width = srcRect->h * fabs(sin(theta) )+ srcRect->w * fabs(cos(theta)) + 0.5;
	int height = srcRect->h * fabs(cos(theta)) + srcRect->w * fabs(sin(theta)) + 0.5;
	double srcRatio = (double)srcRect->w / srcRect->h;
	double srcBorderRatio = (double)width / height;
	double dstRatio = (double)dstRect->w / dstRect->h;
	//計算邊框縮放到目標區(qū)域的大小
	int zoomWidth;
	int zoomHeight;
	if (srcBorderRatio > dstRatio)
	{
		zoomWidth = dstRect->w;
		zoomHeight = dstRect->w / srcBorderRatio;
	}
	else
	{
		zoomWidth = dstRect->h * srcBorderRatio;
		zoomHeight = dstRect->h;
	}
	//通過縮放后的邊框計算還原的圖像大小
	targetRect.h = (double)zoomWidth / (fabs(sin(theta) )+ srcRatio * fabs(cos(theta)));
	targetRect.w = targetRect.h * srcRatio;
	targetRect.x = (dstRect->w- targetRect.w ) / 2;
	targetRect.y = (dstRect->h- targetRect.h ) / 2;
	return targetRect;
}

	//窗口區(qū)域
	sdlRect.x = 0;
	sdlRect.y = 0;
	sdlRect.w = video->screen_w;
	sdlRect.h = video->screen_h;
	//視頻區(qū)域
	sdlRect2.x = 0;
	sdlRect2.y = 0;
	sdlRect2.w = video->decoder.codecContext->width;
	sdlRect2.h = video->decoder.codecContext->height;
	//渲染到sdl窗口
	SDL_RenderClear(video->sdlRenderer);
	SDL_UpdateYUVTexture(video->sdlTexture, &sdlRect2, dst_data[0], dst_linesize[0], dst_data[1], dst_linesize[1], dst_data[2], dst_linesize[2]);
	if (video->angle == 0)
		SDL_RenderCopy(video->sdlRenderer, video->sdlTexture, NULL, &sdlRect);
	else
	//當旋轉角度不為0時使用SDL_RenderCopyEx渲染
	{
		SDL_Rect sdlRect3;
		//計算旋轉后的目標區(qū)域
		sdlRect3= getRotateRect(&sdlRect2,&sdlRect,video->angle);
		SDL_RenderCopyEx(video->sdlRenderer, video->sdlTexture, NULL
			, &sdlRect3, video->angle, 0, SDL_FLIP_NONE);
	}
	SDL_RenderPresent(video->sdlRenderer);