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月份:2013年2月

判断线段和矩形是否相交

判断线段和矩形是否相交

阅读本文,你可以了解 AS3中判断线段和矩形是否相交的一种方法。

实例如下:

RectLine

 

源码如下:(判断方法来自网上,原方法是java的)

[codesyntax lang=”php”]

package
{
	import flash.display.Sprite;
	import flash.events.MouseEvent;
	import flash.text.TextField;

	[SWF(width=375,height=300,backgroundColor="0xeeeeee")]
	public class RectLine extends Sprite
	{
		private var txt:TextField;
		public function RectLine()
		{

			this.txt = new TextField();
			addChild(txt);

			stage.addEventListener(MouseEvent.CLICK,ckHandler);
			ckHandler(null);
		}

		private function ckHandler(e:MouseEvent):void
		{
			graphics.clear();
			graphics.beginFill(0x00ffff);
			graphics.drawRect(100,100,200,50);
			graphics.endFill();

			var a:int = Math.random()*375;
			var b:int = Math.random()*300;
			var c:int = Math.random()*375;
			var d:int = Math.random()*300;

			graphics.lineStyle(2,0xff0000);
			graphics.moveTo(a,b);
			graphics.lineTo(c,d);
			trace(isLineIntersectRectangle(a,b,c,d,100,100,300,150));
			var isF:Boolean = isLineIntersectRectangle(a,b,c,d,100,100,300,150);
			txt.text = "是否相交:"+isF;
		}

		/** <p>判断线段是否在矩形内 </p>
		 * 先看线段所在直线是否与矩形相交,
		 * 如果不相交则返回false,
		 * 如果相交,
		 * 则看线段的两个点是否在矩形的同一边(即两点的x(y)坐标都比矩形的小x(y)坐标小,或者大),
		 * 若在同一边则返回false,
		 * 否则就是相交的情况。
		 * @param linePointX1 线段起始点x坐标
		 * @param linePointY1 线段起始点y坐标
		 * @param linePointX2 线段结束点x坐标
		 * @param linePointY2 线段结束点y坐标
		 * @param rectangleLeftTopX 矩形左上点x坐标
		 * @param rectangleLeftTopY 矩形左上点y坐标
		 * @param rectangleRightBottomX 矩形右下点x坐标
		 * @param rectangleRightBottomY 矩形右下点y坐标
		 * @return 是否相交
		 */
		private function isLineIntersectRectangle(linePointX1:Number,
												  linePointY1:Number,
												  linePointX2:Number,
												  linePointY2:Number,
												  rectangleLeftTopX:Number,
												  rectangleLeftTopY:Number,
												  rectangleRightBottomX:Number,
												  rectangleRightBottomY:Number):Boolean
		{
			var  lineHeight:Number = linePointY1 - linePointY2;
			var lineWidth:Number = linePointX2 - linePointX1;  // 计算叉乘
			var c:Number = linePointX1 * linePointY2 - linePointX2 * linePointY1;
			if ((lineHeight * rectangleLeftTopX + lineWidth * rectangleLeftTopY + c >= 0 && lineHeight * rectangleRightBottomX + lineWidth * rectangleRightBottomY + c <= 0)
				|| (lineHeight * rectangleLeftTopX + lineWidth * rectangleLeftTopY + c <= 0 && lineHeight * rectangleRightBottomX + lineWidth * rectangleRightBottomY + c >= 0)
				|| (lineHeight * rectangleLeftTopX + lineWidth * rectangleRightBottomY + c >= 0 && lineHeight * rectangleRightBottomX + lineWidth * rectangleLeftTopY + c <= 0)
				|| (lineHeight * rectangleLeftTopX + lineWidth * rectangleRightBottomY + c <= 0 && lineHeight * rectangleRightBottomX + lineWidth * rectangleLeftTopY + c >= 0))
			{

				if (rectangleLeftTopX > rectangleRightBottomX) {
					var temp:Number = rectangleLeftTopX;
					rectangleLeftTopX = rectangleRightBottomX;
					rectangleRightBottomX = temp;
				}
				if (rectangleLeftTopY < rectangleRightBottomY) {
					var temp1:Number = rectangleLeftTopY;
					rectangleLeftTopY = rectangleRightBottomY;
					rectangleRightBottomY = temp1;   }
				if ((linePointX1 < rectangleLeftTopX && linePointX2 < rectangleLeftTopX)
					|| (linePointX1 > rectangleRightBottomX && linePointX2 > rectangleRightBottomX)
					|| (linePointY1 > rectangleLeftTopY && linePointY2 > rectangleLeftTopY)
					|| (linePointY1 < rectangleRightBottomY && linePointY2 < rectangleRightBottomY)) {
					return false;
				} else {
					return true;
				}
			} else {
				return false;
			}
		}
	}
}

[/codesyntax]

延伸思考:1.旋转后的矩形 是否还能用这个方法进行判断?

2.直线与其他形状(如椭圆)如何判断相交?

延伸阅读:公式汇总 http://blog.sqstudio.com/formula