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 {

	@Override
	protected 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);
		}

		@Override
		protected 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 empty
			mPath.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)