C++ sdl实现渲染旋转视频的方法分享

//srcRect为视频区域，angle为旋转角度
const double PI = 3.1415926535897935384626;
//角度转弧度，用于三角函数计算。
double theta = PI / 180.0 * angle;
//计算旋转后的边框大小，+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;

//边框的宽高比
double srcBorderRatio = (double)width / height;
//目标区域的宽高比
double dstRatio = (double)dstRect->w / dstRect->h;
//计算边框缩放到目标区域的大小
int zoomWidth;
int zoomHeight;
if (srcBorderRatio > dstRatio)
{
	zoomWidth = dstRect->w;
	zoomHeight = dstRect->w / srcBorderRatio;
}
else
{
	zoomWidth = dstRect->h * srcBorderRatio;
	zoomHeight = dstRect->h;
}

//视频的宽高比
double srcRatio = (double)srcRect->w / srcRect->h;
//通过缩放后的边框计算还原的图像大小
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>
/// 计算旋转的矩形大小
/// </summary>
/// <param name="src">原图像区域</param>
/// <param name="dst">目标区域</param>
/// <param name="angle">旋转角度</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;
	//计算旋转后的边框大小
	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;
	//计算边框缩放到目标区域的大小
	int zoomWidth;
	int zoomHeight;
	if (srcBorderRatio > dstRatio)
	{
		zoomWidth = dstRect->w;
		zoomHeight = dstRect->w / srcBorderRatio;
	}
	else
	{
		zoomWidth = dstRect->h * srcBorderRatio;
		zoomHeight = dstRect->h;
	}
	//通过缩放后的边框计算还原的图像大小
	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;
}

	//窗口区域
	sdlRect.x = 0;
	sdlRect.y = 0;
	sdlRect.w = video->screen_w;
	sdlRect.h = video->screen_h;
	//视频区域
	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
	//当旋转角度不为0时使用SDL_RenderCopyEx渲染
	{
		SDL_Rect sdlRect3;
		//计算旋转后的目标区域
		sdlRect3= getRotateRect(&sdlRect2,&sdlRect,video->angle);
		SDL_RenderCopyEx(video->sdlRenderer, video->sdlTexture, NULL
			, &sdlRect3, video->angle, 0, SDL_FLIP_NONE);
	}
	SDL_RenderPresent(video->sdlRenderer);