8.3.6 Paint API之—— Xfermode与PorterDuff详解(三)

本节引言：

1.要实现的效果图以及实现流程分析：

运行后的效果图：

嗯，上述就是我们要实现的一个效果，通过这个PorterDuff.Mode.DST_IN模式来实现！ 我们来分析分析实现流程：

大体的实现流程如上述，知道流程再看代码就简单很多了！

2.代码实现：

自定义控件属性：res/attrs.xml：

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <declare-styleable name="CircleImageView">
        <attr name="Radius" format="dimension"/>
        <attr name="type">
            <enum name="circle" value="0"/>
            <enum name="round" value="1"/>
        </attr>
    </declare-styleable>
</resources>

接着是自定义ImageView：CircleImageView.java：

/**
 * Created by Jay on 2015/10/25 0025.
 */
public class CircleImageView extends ImageView {

    private Paint mPaint;
    private Xfermode mXfermode = new PorterDuffXfermode(PorterDuff.Mode.DST_IN);
    private Bitmap mMaskBitmap;
    private WeakReference<Bitmap> mWeakBitmap;

    //图片相关的属性
    private int type;                           //类型，圆形或者圆角
    public static final int TYPE_CIRCLE = 0;
    public static final int TYPE_ROUND = 1;
    private static final int BODER_RADIUS_DEFAULT = 10;     //圆角默认大小值
    private int mBorderRadius;                  //圆角大小


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

    public CircleImageView(Context context, AttributeSet attrs) {
        super(context, attrs);
        mPaint = new Paint();
        mPaint.setAntiAlias(true);
        //取出attrs中我们为View设置的相关值
        TypedArray tArray = context.obtainStyledAttributes(attrs, R.styleable.CircleImageView);
        mBorderRadius = tArray.getDimensionPixelSize(R.styleable.CircleImageView_Radius, BODER_RADIUS_DEFAULT);
        type = tArray.getInt(R.styleable.CircleImageView_type, TYPE_CIRCLE);
        tArray.recycle();
    }

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


    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        if (type == TYPE_CIRCLE) {
            int width = Math.min(getMeasuredWidth(), getMeasuredHeight());
            setMeasuredDimension(width, width);    //设置当前View的大小
        }
    }

    @Override
    protected void onDraw(Canvas canvas) {

        //在缓存中取出bitmap
        Bitmap bitmap = mWeakBitmap == null ? null : mWeakBitmap.get();
        if (bitmap == null || bitmap.isRecycled()) {
            //获取图片宽高
            Drawable drawable = getDrawable();
            int width = drawable.getIntrinsicWidth();
            int height = drawable.getIntrinsicHeight();

            if (drawable != null) {
                bitmap = Bitmap.createBitmap(getWidth(), getHeight(), Bitmap.Config.ARGB_8888);
                Canvas drawCanvas = new Canvas(bitmap);
                float scale = 1.0f;
                if (type == TYPE_ROUND) {
                    scale = Math.max(getWidth() * 1.0f / width, getHeight()
                            * 1.0f / height);
                } else {
                    scale = getWidth() * 1.0F / Math.min(width, height);
                }
                //根据缩放比例，设置bounds，相当于缩放图片了
                drawable.setBounds(0, 0, (int) (scale * width),
                        (int) (scale * height));

                drawable.draw(drawCanvas);
                if (mMaskBitmap == null || mMaskBitmap.isRecycled()) {
                    mMaskBitmap = getBitmap();
                }

                mPaint.reset();
                mPaint.setFilterBitmap(false);
                mPaint.setXfermode(mXfermode);

                //绘制形状
                drawCanvas.drawBitmap(mMaskBitmap, 0, 0, mPaint);

                //bitmap缓存起来，避免每次调用onDraw，分配内存
                mWeakBitmap = new WeakReference<Bitmap>(bitmap);

                //绘制图片
                canvas.drawBitmap(bitmap, 0, 0, null);
                mPaint.setXfermode(null);

            }
        }
        if (bitmap != null) {
            mPaint.setXfermode(null);
            canvas.drawBitmap(bitmap, 0.0f, 0.0f, mPaint);
            return;
        }
    }

    //缓存Bitmap，避免每次OnDraw都重新分配内存与绘图
    @Override
    public void invalidate() {
        mWeakBitmap = null;
        if (mWeakBitmap != null) {
            mMaskBitmap.recycle();
            mMaskBitmap = null;
        }
        super.invalidate();
    }

    //定义一个绘制形状的方法

    private Bitmap getBitmap() {
        Bitmap bitmap = Bitmap.createBitmap(getWidth(), getHeight(),
                Bitmap.Config.ARGB_8888);

        Canvas canvas = new Canvas(bitmap);
        Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);   //抗锯齿
        paint.setColor(Color.BLACK);
        if (type == TYPE_ROUND) {
            canvas.drawRoundRect(new RectF(0, 0, getWidth(), getHeight()),
                    mBorderRadius, mBorderRadius, paint);
        } else {
            canvas.drawCircle(getWidth() / 2, getWidth() / 2, getWidth() / 2, paint);
        }
        return bitmap;
    }
}

最后在布局文件那里调用下:activity_main.xml：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <com.jay.xfermodedemo1.CircleImageView
        android:layout_width="160dp"
        android:layout_height="240dp"
        android:layout_margin="10dp"
        android:src="@mipmap/ic_bg_meizi2"
        app:type="circle" />

    <com.jay.xfermodedemo1.CircleImageView
        android:layout_width="160dp"
        android:layout_height="280dp"
        android:layout_margin="10dp"
        android:src="@mipmap/ic_bg_meizi1"
        app:Radius="30dp"
        app:type="round" />
    
</LinearLayout>

好的，代码一次看不懂，看多两次就懂的了~

3.本节代码示例下载：

XfermodeDemo1.zip

本节小结：