8.3.7 Paint API之—— Xfermode与PorterDuff详解(四)

本节引言：

1.要实现的效果图以及实现流程分析：

要实现的效果图：

可能看上去有点复杂，其实不然，代码超简单的说~

2.代码实现：

直接就一个自定义View——StripMeiZi.java

/**
 * Created by Jay on 2015/10/25 0025.
 */
public class StripMeiZi extends View{

    private Paint mPaint = new Paint();
    private Path mPath = new Path();
    private Canvas mCanvas;
    private Bitmap mBeforeBitmap;
    private Bitmap mBackBitmap;
    private int mLastX,mLastY;
    private int screenW, screenH; //屏幕宽高
    private Xfermode mXfermode = new PorterDuffXfermode(PorterDuff.Mode.DST_OUT);


    public StripMeiZi(Context context) {
        this(context, null);
    }

    public StripMeiZi(Context context, AttributeSet attrs) {
        super(context, attrs);
        screenW = ScreenUtil.getScreenW(context);
        screenH = ScreenUtil.getScreenH(context);
        init();
    }


    public StripMeiZi(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    private void init() {
        //背后图片，这里让它全屏
        mBackBitmap = BitmapFactory.decodeResource(getResources(), R.mipmap.meizi_back);
        mBackBitmap = Bitmap.createScaledBitmap(mBackBitmap, screenW, screenH, false);
        //前面的图片，并绘制到Canvas上
        mBeforeBitmap = Bitmap.createBitmap(screenW, screenH, Bitmap.Config.ARGB_8888);
        mCanvas = new Canvas(mBeforeBitmap);
        mCanvas.drawBitmap(BitmapFactory.decodeResource(getResources(),
                R.mipmap.meizi_before), null, new RectF(0, 0, screenW, screenH), null);
        //画笔相关的设置
        mPaint.setAntiAlias(true);
        mPaint.setDither(true);
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setStrokeJoin(Paint.Join.ROUND); // 圆角
        mPaint.setStrokeCap(Paint.Cap.ROUND); // 圆角
        mPaint.setStrokeWidth(80);    // 设置画笔宽
    }

    private void drawPath() {
        mPaint.setXfermode(mXfermode);
        mCanvas.drawPath(mPath, mPaint);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        canvas.drawBitmap(mBackBitmap, 0, 0, null);
        drawPath();
        canvas.drawBitmap(mBeforeBitmap, 0, 0, null);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        int action = event.getAction();
        int x = (int) event.getX();
        int y = (int) event.getY();
        switch (action)
        {
            case MotionEvent.ACTION_DOWN:
                mLastX = x;
                mLastY = y;
                mPath.moveTo(mLastX, mLastY);
                break;
            case MotionEvent.ACTION_MOVE:

                int dx = Math.abs(x - mLastX);
                int dy = Math.abs(y - mLastY);

                if (dx > 3 || dy > 3)
                    mPath.lineTo(x, y);

                mLastX = x;
                mLastY = y;
                break;
        }
        invalidate();
        return true;
    }
}

布局代码activity_main.xml：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <com.jay.xfermodedemo2.StripMeiZi
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

</RelativeLayout>