PorterDuffXfermode的简单使用之画圆形头像

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PorterDuffXfermode的用法之教你画圆形头像

这里我们就直接在onDraw方法中操作了,首先应该创建一个画笔,需要注意的是,创建的画笔不要设置style为stroke,使用默认的即可.
根据源图实例化一个Bitmap对象,bitmap = BitmapFactory.decodeResource(getResources(),R.drawable.timg);然后再利用该实例创建一个副本(因为Android系统中,是不允许直接修改源图的):bmp = Bitmap.createBitmap(bitmap.getWidth(), bitmap.getHeight(),Bitmap.Config.ARGB_8888);
根据Bitmap副本创建一个Canvas对象Canvas mCanvas = new Canvas(bmp);表示之后的绘画操作都是发生在这个副本上的.
然后利用创建出来的mCanvas对象来画一个圆形遮罩mCanvas.drawCircle(bitmap.getWidth() / 2, bitmap.getHeight() / 2,bitmap.getWidth() / 2, paint2);
接下来就是关键步骤了paint2.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));这里就用到了PorterDuffXfermode类了,它就是用来设置draw方法之前和之后图像的关系的:
然后将源图画在mCanvas对象上mCanvas.drawBitmap(bitmap, 0, 0, paint2);
此时副本上的图像就画好了,最后将这个Bitmap画到onDraw方法中指定canvas对象上canvas.drawBitmap(bmp, 0, 0, paint1);

完整代码:

package com.qianyue.testdensity;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.Paint.Style;import android.graphics.PorterDuff;import android.graphics.PorterDuffXfermode;import android.graphics.RectF;import android.util.AttributeSet;import android.view.View;public class DrawPaint extends View {    private static final float WIDTH = 5;    Paint paint1;    Paint paint2;    private Bitmap bitmap;    private Bitmap bmp;public DrawPaint(Context context, AttributeSet attrs) {    this(context, attrs, 0);}public DrawPaint(Context context, AttributeSet attrs, int defStyle) {    super(context, attrs, defStyle);    init();}public DrawPaint(Context context) {    this(context, null);}private void init() {    paint1 = new Paint();    paint1.setColor(Color.RED);    paint1.setStrokeWidth(WIDTH);    paint2 = new Paint();    paint2.setAntiAlias(true);    paint2.setStrokeWidth(WIDTH);    setBackgroundColor(Color.TRANSPARENT);    bitmap = BitmapFactory.decodeResource(getResources(),            R.drawable.timg);    bmp = Bitmap.createBitmap(bitmap.getWidth(), bitmap.getHeight(),            Bitmap.Config.ARGB_8888);}@Overrideprotected void onDraw(Canvas canvas) {    Canvas mCanvas = new Canvas(bmp);    mCanvas.drawCircle(bitmap.getWidth() / 2, bitmap.getHeight() / 2,            bitmap.getWidth() / 2, paint2);    paint2.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));    mCanvas.drawBitmap(bitmap, 0, 0, paint2);    canvas.drawBitmap(bmp, 0, 0, paint1);}@Overrideprotected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {    int getWidth = bitmap.getWidth();    int getHeight = bitmap.getHeight();    int widthMode = MeasureSpec.getMode(widthMeasureSpec);    int heightMode = MeasureSpec.getMode(heightMeasureSpec);    int newWidth = MeasureSpec.makeMeasureSpec(getWidth, widthMode);    int newHeight = MeasureSpec.makeMeasureSpec(getHeight, heightMode);    super.onMeasure(newWidth, newHeight);}}

效果图

v怪客

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