BitmapShader将图片转化为圆形图片

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今天用BitmapShader实现圆形图片

package com.example.bitmap_porterduffxfermode;import android.content.Context;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.graphics.BitmapShader;import android.graphics.Canvas;import android.graphics.Paint;import android.graphics.Shader;import android.util.AttributeSet;import android.view.View;import android.view.View.MeasureSpec;public class RoundRectShaderView extends View {private int mMeasureHeigth;private int mMeasureWidth;private BitmapShader mBitmapShader;private Bitmap mBitmap;private Paint mPaint;public RoundRectShaderView(Context context) {super(context);}public RoundRectShaderView(Context context, AttributeSet attrs) {super(context, attrs);}public RoundRectShaderView(Context context, AttributeSet attrs,int defStyleAttr) {super(context, attrs, defStyleAttr);}@Overrideprotected void onMeasure(int widthMeasureSpec,int heightMeasureSpec) {mMeasureWidth = MeasureSpec.getSize(widthMeasureSpec);mMeasureHeigth = MeasureSpec.getSize(heightMeasureSpec);setMeasuredDimension(mMeasureWidth, mMeasureHeigth);}@Overrideprotected void onDraw(Canvas canvas) {float length = 0;if (mMeasureHeigth >= mMeasureWidth) {length = mMeasureWidth;} else {length = mMeasureHeigth;}mBitmap = BitmapFactory.decodeResource(getResources(),R.drawable.zhongyu);mBitmapShader = new BitmapShader(mBitmap,Shader.TileMode.CLAMP, Shader.TileMode.CLAMP);mPaint = new Paint();mPaint.setShader(mBitmapShader);canvas.drawCircle(length/2, length/2, length/2, mPaint);}}

然后在布局文件中引用就行了

  <com.example.bitmap_porterduffxfermode.RoundRectShaderView        android:layout_width="200dp"        android:layout_height="200dp"        android:layout_gravity="center_horizontal" >    </com.example.bitmap_porterduffxfermode.RoundRectShaderView>

测量一下View的高度，根据测量的高度设置遮罩层的大小，情况是这样，如果绘制的圆形小于图像大小，之会显示部分图像

弄清原理就明白了.

到底如何才能实现缩放图像大小呢？

解决方法：http://blog.csdn.net/wei_chong_chong/article/details/51125258

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