初学PorterDuffXfermode（实现刮刮乐）_porterduff. 刮刮乐-优快云博客

本文介绍了一种自定义Android View的方法，通过XfermodeView实现了特定的绘图效果。利用PorterDuffXfermode结合DST_IN模式，使得触摸路径与背景图片产生有趣的交互效果。文章详细展示了如何创建自定义View，包括初始化画布、绘制背景图片及灰色前景图片，并通过触摸事件绘制路径。

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自定义View
XfermodeView.java

package com.example.day0119;

import java.util.Formatter.BigDecimalLayoutForm;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffXfermode;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

public class XfermodeView extends View{

    private Paint mPaint;
    private Canvas mCanvas;
    private Path mPath;
    private Bitmap mBgBitmap,mFgBitmap;
    public XfermodeView(Context context, AttributeSet attrs) {
        super(context, attrs);

        mPaint = new Paint();
        mPaint.setAlpha(0);//透明
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setStrokeJoin(Paint.Join.ROUND);//笔头设置为圆形
        mPaint.setStrokeCap(Paint.Cap.ROUND);//笔尾设置为圆形
        mPaint.setAntiAlias(true);
        mPaint.setStrokeWidth(50);
        mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_IN));//显示交错的下层图片

        mPath = new Path();

        mBgBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.bmp);
        mFgBitmap = Bitmap.createBitmap(mBgBitmap.getWidth(), mBgBitmap.getHeight(), Bitmap.Config.ARGB_8888);

        mCanvas = new Canvas(mFgBitmap);
        mCanvas.drawColor(Color.GRAY);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        canvas.drawBitmap(mBgBitmap, 0, 0, null);
        canvas.drawBitmap(mFgBitmap, 0, 0, null);

    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN:
            mPath.reset();
            mPath.moveTo(event.getX(), event.getY());
            break;

        case MotionEvent.ACTION_MOVE :
            mPath.lineTo(event.getX(), event.getY());
            break;
        }

        mCanvas.drawPath(mPath, mPaint);
        invalidate();
        return true;
    }

}

xml

<FrameLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
xmlns:android="http://schemas.android.com/apk/res/android" >

    <com.example.day0119.XfermodeView 
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

</FrameLayout>

效果

这里写图片描述