Android 自定义view中如何判断一个点是否在 经过旋转的 RectF 内？

最近在做相册的图片编辑功能，遇到一个bug，插入文字后旋转文字区域，点击文字区域无法触发，分析原因是判断时认定为点没在RectF内。如图：

如果只是通过rect.contains(x, y)来判断，那么实际区域则是绿色区域的部分，则有部分无法点击，如下图：

因此需要将矩形框旋转。

如果通过matrix.mapRect(rect)来获取转换后的区域，再通过rect.contains(x, y)来判断是否落在区域内，那么实际区域如下图绿色区域，则点击非区域内的位置仍会触发文字区域的点击，如下图：

Matrix matrix = new Matrix();
matrix.setRotate(roatetAngle, mHelpBoxRect.centerX(), mHelpBoxRect.centerY());
matrix.mapRect(mHelpBoxRect);

因此，无法通过rect.contains(x, y)来判断点是否落在区域内。需要将原矩形四个顶点旋转，将转换后的矩形四个顶点重新构成四边形，再判断点是否落在该四边形内。

public boolean clickHelpBoxRect(float x, float y) {
		if (mHelpBoxRect == null || mHelpBoxRect.isEmpty()) {
			return false;
		}
		boolean isClickHelpBoxRect;
		if (roatetAngle != 0) {
			// 旋转后判断点是否在四边形内
			Matrix matrix = new Matrix();
			matrix.setRotate(roatetAngle, mHelpBoxRect.centerX(), mHelpBoxRect.centerY());

			PointF curPoint = new PointF(x, y);

			PointF pointLT = getMapPoints(matrix, mHelpBoxRect.left, mHelpBoxRect.top);
			PointF pointRT = getMapPoints(matrix, mHelpBoxRect.right, mHelpBoxRect.top);
			PointF pointLB = getMapPoints(matrix, mHelpBoxRect.left, mHelpBoxRect.bottom);
			PointF pointRB = getMapPoints(matrix, mHelpBoxRect.right, mHelpBoxRect.bottom);
			isClickHelpBoxRect = pointInRect(curPoint, pointLT, pointRT, pointLB, pointRB);
		} else {
			isClickHelpBoxRect = mHelpBoxRect.contains(x, y);
		}
		return isClickHelpBoxRect;
	}

	/**
	 * 获取旋转后的座标点
	 *
	 * @param matrix 转换矩阵
	 * @param x      左座标
	 * @param y      右座标
	 * @return
	 */
	private PointF getMapPoints(Matrix matrix, float x, float y) {
		float[] floats = new float[]{x, y};
		matrix.mapPoints(floats);
		return new PointF(floats[0], floats[1]);
	}

	/**
	 * 点是否落在四边形内
	 *
	 * @param curPoint 点击位置
	 * @param pointLT  左上顶点
	 * @param pointRT  右上顶点
	 * @param pointLB  左下顶点
	 * @param pointRB  右下顶点
	 * @return true 在四边形内；false 不在四边形内
	 */
	private boolean pointInRect(PointF curPoint, PointF pointLT, PointF pointRT, PointF pointLB, PointF pointRB) {
		int nCount = 4;
		PointF[] rectPoints = new PointF[]{pointLT, pointLB, pointRB, pointRT};
		int nCross = 0;
		for (int i = 0; i < nCount; i++) {
			//依次取相邻的两个点
			PointF pStart = rectPoints[i];
			PointF pEnd = rectPoints[(i + 1) % nCount];

			//相邻的两个点是平行于x轴的，肯定不相交，忽略
			if (pStart.y == pEnd.y)
				continue;

			//交点在pStart,pEnd的延长线上，pCur肯定不会与pStart.pEnd相交，忽略
			if (curPoint.y < Math.min(pStart.y, pEnd.y) || curPoint.y > Math.max(pStart.y, pEnd.y))
				continue;

			//求当前点和x轴的平行线与pStart,pEnd直线的交点的x座标
			double x = (double) (curPoint.y - pStart.y) * (double) (pEnd.x - pStart.x) / (double) (pEnd.y - pStart.y) + pStart.x;

			//若x座标大于当前点的座标，则有交点
			if (x > curPoint.x)
				nCross++;
		}

		// 单边交点为偶数，点在多边形之外
		return (nCross % 2 == 1);
	}