OpenCV-waitKey()

学习仿射变换时用到waitKey()实现图片旋转显示

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waitKey(30)

for（；；）{
if (waitKey(30) >= 0)//返回30ms内按下的键值，否则返回-1.
break;
}

其中（）内的值表示等待时间（ms），如代码中表示等待30ms，waitKey(30)返回值为30ms内键盘按下的返回值(键盘中每个按键对应一个ASCII码，见https://www.cnblogs.com/yiven/p/7118056.html)
如果没有按键按下，则返回-1，所以不会跳出循环

waitKey(0)

表示一直等待用户按键事件发生

 int main()
{
	Mat src = imread("lyj.png");
	imshow("this is 林宥嘉",src);
	Point2f srcTri[] = {
		Point2f(0,0),
		Point2f(src.cols - 1,0),
		Point2f(0,src.rows - 1),
	};
	Point2f dstTri[] = {
		Point2f(0,src.rows*0.33f),
		Point2f(src.cols*0.85f,src.rows*0.25f),
		Point2f(src.cols*0.15f,src.rows*0.9f),	
	};
	//compute affine matrix
	Mat warp_mat = getAffineTransform(srcTri, dstTri);
	Mat dst, dst2;
	warpAffine(src, dst, warp_mat, src.size(), INTER_LINEAR, BORDER_CONSTANT, Scalar());
	for (int i = 0; i < 3; i++)
		circle(dst, dstTri[i], 5, Scalar(255, 0, 255), -1, 16);
	imshow("Affine Transform Test", dst);
     waitKey(0);
	//Rotation
	for (int frame = 0;; ++frame) {
	Point2f	 center=Point2f(src.cols*0.5f, src.rows*0.5f);
		double angle = frame * 3 % 360, scale = (cos((angle - 60)*PI / 180) + 1.05)*0.8;
		Mat rot_mat = getRotationMatrix2D(center, angle, scale);
		warpAffine(src, dst2, rot_mat, src.size(), INTER_LINEAR, BORDER_CONSTANT, Scalar());
		imshow("Affine Transform Test2", dst2);
		if (waitKey(30) >= 0)//返回30ms内按下的键值，否则返回-1.
			break;

	}
	return 0;
}