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Android中贝塞尔曲线的绘制方法
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貝塞爾曲線，很多人可能不太了解，什么叫做貝塞爾曲線呢？這里先做一下簡單介紹：貝塞爾曲線也可以叫做貝濟埃曲線或者貝茲曲線，它由線段與節點組成，節點是可拖動的支點，線段像可伸縮的皮筋。一般的矢量圖形軟件常利用貝塞爾曲線來精確畫出曲線。
?????? 上面的介紹中，“線段像可伸縮的皮筋”這句話非常關鍵，但也特別好理解。至于貝塞爾曲線的詳細內容大家可以查閱相關資料。
???????Android提供的貝塞爾曲線繪制接口
???????在Android開發中，要實現貝塞爾曲線其實還是很簡單的，因為Android已經給我們提供了相關接口，但此接口方法被藏的有點深，藏于Path類中。此方法如下：
???????android.graphics.Path.quadTo(float x1, float y1, float x2, float y2)
?????? Since: API Level 1
?????? 參數說明：
?????? x1：操作點的x坐標
?????? y1：操作點的y坐標
?????? x2：結束點的x坐標
?????? y2：結束點的y坐標
?????? 從API中看出，貝塞爾曲線從API－1就開始支持了。
???????Android貝塞爾曲線的繪制實例
?????? 熟悉方法后，下面就來實現：
???????SurfaceView框架不多講，看過我博客的都應該知道的。
?????? 直接看MySurfaceView類，此類繼承SurfaceView，是游戲的主視圖。
?????? 這里為了更清晰的講解：這里部分代碼先不貼出來了，最后會整體貼出。
?????? 首先是定義相關的成員變量：
Java代碼 private?int?startX,?startY,?controlX,?controlY,?endX,?endY; ??private?Path?path; ??private?Paint?paintQ; ??private?Random?random;?? ?????? 本類構造函數：
Java代碼 public?MySurfaceView(Context?context)?{ ??????super(context); ??????... ??????????????????path?=?new?Path(); ??????????paintQ?=?new?Paint(); ??????????paintQ.setAntiAlias(true); ??????????paintQ.setStyle(Style.STROKE); ??????????paintQ.setStrokeWidth(5); ??????????paintQ.setColor(Color.WHITE); ??????????random?=?new?Random(); ??????... ??}?? ?????? 接著我把貝賽爾曲線的繪制封裝成一個方法了，函數如下：
Java代碼 public?void?drawQpath(Canvas?canvas)?{ ??????path.reset();????????path.moveTo(startX,?startY); ??????????path.quadTo(controlX,?controlY,?endX,?endY); ??????????canvas.drawPath(path,?paintQ); ??}?? ?????? 最后是用戶觸屏監聽函數以及邏輯函數：
Java代碼 @Override??public?boolean?onTouchEvent(MotionEvent?event)?{ ??????endX?=?(int)?event.getX(); ??????endY?=?(int)?event.getY(); ??????return?true; ??} ??private?void?logic()?{ ??????if?(endX?!=?0?&&?endY?!=?0)?{ ??????????????????controlX?=?random.nextInt((endX?-?startX)?/?2); ??????????controlY?=?random.nextInt((endY?-?startY)?/?2); ??????} ??}?? ?????? 整個代碼很easy，主要是貝賽爾函數的參數，尤其是操作點，操作點的各種不同可以實現不同的效果，這里我簡單的統一的講操作點設置成用戶觸屏點的x、y的一半，呵呵偷懶了~~
???????我把貝賽爾的操作點寫在了邏輯logic()函數中，不斷的執行，并且每次利用nextInt函數得到隨機的操作點，主要為了讓其曲線不斷的變化從而形成一個震動的曲線運動軌跡。
???????運行效果截圖如下：
?????? 這里可能由于圖片是靜止的，所以效果看起來不是很明顯，大家可以運行源碼來觀察。
?????? 下面貼出整個MySurfaceView的源碼：
Java代碼 package?com.qpath; ??import?java.util.Random; ??import?android.content.Context; ??import?android.graphics.Canvas; ??import?android.graphics.Color; ??import?android.graphics.Paint; ??import?android.graphics.Paint.Style; ??import?android.graphics.Path; ??import?android.view.KeyEvent; ??import?android.view.MotionEvent; ??import?android.view.SurfaceHolder; ??import?android.view.SurfaceHolder.Callback; ??import?android.view.SurfaceView; ??public?class?MySurfaceView?extends?SurfaceView?implements?Callback,?Runnable?{ ??????private?SurfaceHolder?sfh; ??????private?Paint?paint; ??????private?Thread?th; ??????private?boolean?flag; ??????private?Canvas?canvas; ??????public?static?int?screenW,?screenH; ??????????????private?int?startX,?startY,?controlX,?controlY,?endX,?endY; ??????????private?Path?path; ??????????private?Paint?paintQ; ??????????private?Random?random; ??????????public?MySurfaceView(Context?context)?{ ??????????super(context); ??????????sfh?=?this.getHolder(); ??????????sfh.addCallback(this); ??????????paint?=?new?Paint(); ??????????paint.setColor(Color.WHITE); ??????????paint.setAntiAlias(true); ??????????setFocusable(true); ??????????????????????????path?=?new?Path(); ??????????paintQ?=?new?Paint(); ??????????paintQ.setAntiAlias(true); ??????????paintQ.setStyle(Style.STROKE); ??????????paintQ.setStrokeWidth(5); ??????????paintQ.setColor(Color.WHITE); ??????????random?=?new?Random(); ??????} ??????????public?void?surfaceCreated(SurfaceHolder?holder)?{ ??????????screenW?=?this.getWidth(); ??????????screenH?=?this.getHeight(); ??????????flag?=?true; ??????????????????th?=?new?Thread(this); ??????????????????th.start(); ??????????????} ??????????public?void?myDraw()?{ ??????????try?{ ??????????????canvas?=?sfh.lockCanvas(); ??????????????if?(canvas?!=?null)?{ ??????????????????canvas.drawColor(Color.BLACK); ??????????????????????????????????drawQpath(canvas); ??????????????} ??????????}?catch?(Exception?e)?{ ??????????????????????}?finally?{ ??????????????if?(canvas?!=?null) ??????????????????sfh.unlockCanvasAndPost(canvas); ??????????} ??????} ??????????public?void?drawQpath(Canvas?canvas)?{ ??????????path.reset();????????????????path.moveTo(startX,?startY); ??????????????????path.quadTo(controlX,?controlY,?endX,?endY); ??????????????????canvas.drawPath(path,?paintQ); ??????} ??????????@Override??????public?boolean?onTouchEvent(MotionEvent?event)?{ ??????????endX?=?(int)?event.getX(); ??????????endY?=?(int)?event.getY(); ??????????return?true; ??????} ??????????private?void?logic()?{ ??????????if?(endX?!=?0?&&?endY?!=?0)?{ ??????????????????????????controlX?=?random.nextInt((endX?-?startX)?/?2); ??????????????controlY?=?random.nextInt((endY?-?startY)?/?2); ??????????} ??????} ??????????@Override??????public?boolean?onKeyDown(int?keyCode,?KeyEvent?event)?{ ??????????return?super.onKeyDown(keyCode,?event); ??????} ??????public?void?run()?{ ??????????while?(flag)?{ ??????????????long?start?=?System.currentTimeMillis(); ??????????????myDraw(); ??????????????logic(); ??????????????long?end?=?System.currentTimeMillis(); ??????????????try?{ ??????????????????if?(end?-?start?<?50)?{ ??????????????????????Thread.sleep(50?-?(end?-?start)); ??????????????????} ??????????????}?catch?(InterruptedException?e)?{ ??????????????????e.printStackTrace(); ??????????????} ??????????} ??????} ??????????public?void?surfaceChanged(SurfaceHolder?holder,?int?format,?int?width, ??????????????int?height)?{ ??????} ??????????public?void?surfaceDestroyed(SurfaceHolder?holder)?{ ??????????flag?=?false; ??????} ??} ?
轉載于:https://www.cnblogs.com/Free-Thinker/p/4749782.html
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