Android下Graphics/Clipping（切割视图）的学习

    看了很多网上很多关于Android切割视图的例子，基本都出自一个人，但作者本人也坦承说不是很了解 Region.Op.下相关： DIFFERENCE INTERSECT UNION XOR REVERSE_DIFFERENCE REPLACE 参数的含义。

   说来也是自己太懒了，这个在APIDmo中有很好的例子。自己仔细研究下就可以明白其中的含义了。

Clipping.java类

  

<span style="font-size:18px;">/* * Copyright (C) 2008 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * *      http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */package com.example.android.apis.graphics;import android.content.Context;import android.graphics.*;import android.os.Bundle;import android.view.View;public class Clipping extends GraphicsActivity {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(new SampleView(this));}private static class SampleView extends View {private Paint mPaint;private Path mPath;public SampleView(Context context) {super(context);setFocusable(true);mPaint = new Paint();mPaint.setAntiAlias(true);mPaint.setStrokeWidth(6);mPaint.setTextSize(16);mPaint.setTextAlign(Paint.Align.RIGHT);mPath = new Path();}private void drawScene(Canvas canvas) {canvas.clipRect(0, 0, 100, 100);canvas.drawColor(Color.WHITE);mPaint.setColor(Color.RED);canvas.drawLine(0, 0, 100, 100, mPaint);mPaint.setColor(Color.GREEN);canvas.drawCircle(30, 70, 30, mPaint);mPaint.setColor(Color.BLUE);canvas.drawText("Clipping", 100, 30, mPaint);}@Overrideprotected void onDraw(Canvas canvas) {canvas.drawColor(Color.GRAY);canvas.save();canvas.translate(10, 10);drawScene(canvas);canvas.restore();canvas.save();canvas.translate(160, 10);canvas.clipRect(10, 10, 90, 90);canvas.clipRect(30, 30, 70, 70, Region.Op.DIFFERENCE);// 扣一块区域drawScene(canvas);canvas.restore();canvas.save();canvas.translate(10, 160);mPath.reset();canvas.clipPath(mPath); // makes the clip emptymPath.addCircle(50, 50, 50, Path.Direction.CCW);canvas.clipPath(mPath, Region.Op.REPLACE);drawScene(canvas);canvas.restore();canvas.save();canvas.translate(160, 160);canvas.clipRect(0, 0, 60, 60);canvas.clipRect(40, 40, 100, 100, Region.Op.UNION);drawScene(canvas);canvas.restore();canvas.save();canvas.translate(10, 310);canvas.clipRect(0, 0, 60, 60);canvas.clipRect(40, 40, 100, 100, Region.Op.XOR);drawScene(canvas);canvas.restore();canvas.save();canvas.translate(160, 310);canvas.clipRect(0, 0, 60, 60);canvas.clipRect(40, 40, 100, 100, Region.Op.REVERSE_DIFFERENCE);drawScene(canvas);canvas.restore();}}}</span>

 

每个图对应相应的代码块很容易理解，clipRect局部绘图区域(明白这个就不至于会为那个drawScene方法而感到迷惑，drawScene(canvas)该方法内部的画布是你传进去的，所以内部的那个局部绘图区域不要理解混了)