AS3 直线裁剪

private var bmp:Bitmap = new Bitmap(bmd);private var clip1:Rectangle = new Rectangle(100,100,100,100);private var clip2:Rectangle = new Rectangle(200,200,200,200);public function LineTest(){stage.scaleMode = StageScaleMode.NO_SCALE;addChild(bmp);stage.addEventListener(Event.ENTER_FRAME, onEnterFrame);}protected function onEnterFrame(event:Event):void{var s:Point = new Point(Math.random()*600, Math.random()*800);var e:Point = new Point(Math.random()*600, Math.random()*800);var s1:Point = s.clone();var e1:Point = e.clone();if(clipLine(s1, e1, clip1)){drawLine(s1,e1, 0xffffff*Math.random());}if(clipLine(s,e,clip2)){drawLine(s,e,0xffffff*Math.random());}}/** *  *  * 看起点和终点属于下列哪个区域 *  *  ||NW |N|  NE || ||------------------------------------------------ || ||W |C|     E || ||------------------------------------------------ ||SW |S|  SE || ||  * @param start * @param end * @param clipRect *  */private function clipLine(start:Point, end:Point, clipRect:Rectangle):int{const CLIP_CODE_C:uint = 0;const CLIP_CODE_W:uint = 1;const CLIP_CODE_E:uint = 2;const CLIP_CODE_S:uint = 4;const CLIP_CODE_N:uint = 8;const CLIP_CODE_SW:uint = 5;const CLIP_CODE_SE:uint = 6;const CLIP_CODE_NW:uint = 9;const CLIP_CODE_NE:uint = 10;//斜率var k:Number = (end.y - start.y)/(end.x - start.x);var krevese:Number = (end.x - start.x)/(end.y - start.y);//计算在X轴和Y轴上裁剪过后的值var xc1:int = start.x;var yc1:int = start.y;var xc2:int = end.x;var yc2:int = end.y;//算起点再哪个区域var p1Code:int = 0;//算终点再哪个区域var p2Code:int = 0;//startif(xc1 < clipRect.left){p1Code |= CLIP_CODE_W;}else if(xc1 > clipRect.right){p1Code |= CLIP_CODE_E;}if(yc1 < clipRect.bottom){p1Code |= CLIP_CODE_N;}else if(yc1 > clipRect.top){p1Code |= CLIP_CODE_S;}//endif(xc2 < clipRect.left){p2Code |= CLIP_CODE_W;}else if(xc2 > clipRect.right){p2Code |= CLIP_CODE_E;}if(yc2 < clipRect.bottom){p2Code |= CLIP_CODE_N;}else if(yc2 > clipRect.top){p2Code |= CLIP_CODE_S;}//这里有个小技巧，判断直线两个端点都落在 裁剪区域之外//||//1001|1000|1010//-------------------------------------//0001|0|0010//||//-------------------------------------//0101|0100|0110//||//以W为例，当两个端点落在  W-WN 或   W-WS 的时候这条直线在矩形外面,其它情况则与矩形有交点//可以看出 在外面的情况 有  p1Code & p2Code != 0 ，有部分落在里面的时候，有 p1Code & p2Code  = 0//所以我们先把直线在裁剪区域之外的排除if(p1Code & p2Code){return 0;}//再判断两个端点完全在 裁剪矩形内的情况//完全在里面则无须裁剪if(p1Code == 0 &&　p2Code == 0){return 1;}//处理一部分在里面的情况//先求出起始点在矩形上的映射switch(p1Code){case CLIP_CODE_C:break;case CLIP_CODE_W:xc1 = clipRect.left;yc1 = start.y + k*(xc1 - start.x);break;case CLIP_CODE_E:xc1 = clipRect.right;yc1 = start.y + k*(xc1 - start.x);break;case CLIP_CODE_S:yc1 = clipRect.bottom;xc1 = start.x + krevese*(yc1 - start.y);break;case CLIP_CODE_N:yc1 = clipRect.top;xc1 = start.x + krevese*(yc1 - start.y);break;case CLIP_CODE_SW://有一个交点会落在外面，所以要判断两次, 取落在矩形上的那个点，画个图就知道了xc1 = clipRect.left;yc1 = start.y + k*(xc1 - start.x);if(yc1 > clipRect.bottom || yc1 < clipRect.top){yc1 = clipRect.bottom;xc1 = start.x + krevese*(yc1 - start.y);}break;case CLIP_CODE_SE:xc1 = clipRect.right;yc1 = start.y + k*(xc1 - start.x);if(yc1 > clipRect.bottom || yc1 < clipRect.top){yc1 = clipRect.bottom;xc1 = start.x + krevese*(yc1 - start.y);}break;case CLIP_CODE_NW:xc1 = clipRect.left;yc1 = start.y + k*(xc1 - start.x);if(yc1 > clipRect.bottom || yc1 < clipRect.top){yc1 = clipRect.top;xc1 = start.x + krevese*(yc1 - start.y);}break;case CLIP_CODE_NE:xc1 = clipRect.right;yc1 = start.y + k*(xc1 - start.x);if(yc1 > clipRect.bottom || yc1 < clipRect.top){yc1 = clipRect.top;xc1 = start.x + krevese*(yc1 - start.y);}break;}//再求出终点在矩形上的映射switch(p2Code){case CLIP_CODE_C:break;case CLIP_CODE_W:xc2 = clipRect.left;yc2 = end.y + k*(xc2 - end.x);break;case CLIP_CODE_E:xc2 = clipRect.right;yc2 = end.y + k*(xc2 - end.x);break;case CLIP_CODE_S:yc2 = clipRect.bottom;xc2 = end.x + krevese*(yc2 - end.y);break;case CLIP_CODE_N:yc2 = clipRect.top;xc2 = end.x + krevese*(yc2 - end.y);break;case CLIP_CODE_SW://有一个交点会落在外面，所以要判断两次, 取落在矩形上的那个点，画个图就知道了xc2 = clipRect.left;yc2 = end.y + k*(xc2 - end.x);if(yc2 > clipRect.bottom || yc2 < clipRect.top){yc2 = clipRect.bottom;xc2 = end.x + krevese*(yc2 - end.y);}break;case CLIP_CODE_SE:xc2 = clipRect.right;yc2 = end.y + k*(xc2 - end.x);if(yc2 > clipRect.bottom || yc2 < clipRect.top){yc2 = clipRect.bottom;xc2 = end.x + krevese*(yc2 - end.y);}break;case CLIP_CODE_NW:xc2 = clipRect.left;yc2 = end.y + k*(xc2 - end.x);if(yc2 > clipRect.bottom || yc2 < clipRect.top){yc2 = clipRect.top;xc2 = end.x + krevese*(yc2 - end.y);}break;case CLIP_CODE_NE:xc2 = clipRect.right;yc2 = end.y + k*(xc2 - end.x);if(yc2 > clipRect.bottom || yc2 < clipRect.top){yc2 = clipRect.top;xc2 = end.x + krevese*(yc2 - end.y);}break;}//double checkif((xc1 < clipRect.left) || (xc1 > clipRect.right) ||(xc2 < clipRect.left) || (xc2 > clipRect.right) ||(yc1 < clipRect.top) || (yc1 > clipRect.bottom) ||(yc2 < clipRect.top) || (yc2 > clipRect.bottom)){return 0;}start.x = xc1;start.y = yc1;end.x = xc2;end.y = yc2;return 1;}private function drawLine(start:Point, end:Point, color:uint):void{bmd.lock();var dx:int = end.x - start.x;var dy:int = end.y - start.y;var x:int = start.x;var y:int = start.y;var xInc:int;var yInc:int;var i:int;if(dx >=0){xInc = 1;}else{xInc = -1;dx = -dx;//总共要走多少步}if(dy >= 0){yInc = 1;}else{yInc = -1;dy = -dy;}//比较值的时候，都是按照第一象限来比较，只不过，步进的时候，按照 xInc, yInc 来步进var k2dx:int = 2*dy;var error2dx:int = k2dx - 1;var k2dy:int = 2*dx;var error2dy:int = k2dy - 1;if(dx >= dy)//近X轴线{for(i = 0; i <= dx ; i++){bmd.setPixel32(x,y, color);if(error2dx > 0){y += yInc;error2dx = error2dx + k2dx - 2*dx;}else{error2dx = error2dx + k2dx;}x += xInc;}}else//近Y轴线{for(i = 0; i <= dy ; i++){bmd.setPixel32(x,y, color);if(error2dy > 0){x += xInc;error2dy = error2dy + k2dy - 2*dy;}else{error2dy = error2dy + k2dy;}y += yInc;}}bmd.unlock();}