CircleImageView实现方法有很多种，各有优缺点，因此需要按照不同的场景使用。我们今天使用修改图片像素的方法实现CircleImageView，主要知识点无非是勾股定理和点到圆形的距离。
素材图片：
效果如下：
1、clipPath裁剪画布
该方法支持的最小版本是Android 4.3(API Level 18)，方便快捷，但是不支持硬件加，此外也存在Path既有的缺点，不支持抗锯齿。
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
Paint paint = new Paint();
mBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.pic);
mPath = new Path();
mPath.addCircle(mBitmap.getWidth() / 2, mBitmap.getHeight() / 2, mBitmap.getWidth() / 2, Path.Direction.CCW);
canvas.clipPath(mPath);
canvas.drawBitmap(mBitmap, 0, 0, paint);
}
2、使用PorterDuffXfermode
PorterDuffXfermode是Android主流的图片合成工具，支持模式多，稳定性强，效果好，质量高，支持抗锯齿备受广大开发者喜爱，可以说是很多应用开发的首选。缺点是难度学习有些高，另外比较占内存。
/**
* 绘制圆形图片
*
*/
@Override
protected void onDraw(Canvas canvas) {
Drawable drawable = getDrawable();
if (null != drawable) {
Bitmap bitmap = ((BitmapDrawable) drawable).getBitmap();
Bitmap b = getCircleBitmap(bitmap);
final Rect rectSrc = new Rect(0, 0, b.getWidth(), b.getHeight());
final Rect rectDest = new Rect(0,0,getWidth(),getHeight());
paint.reset();
canvas.drawBitmap(b, rectSrc, rectDest, paint);
} else {
super.onDraw(canvas);
}
}
/**
* 获取圆形图片方法
* @param bitmap
* @param pixels
* @return Bitmap
*/
private Bitmap getCircleBitmap(Bitmap bitmap) {
Bitmap output = Bitmap.createBitmap(bitmap.getWidth(),
bitmap.getHeight(), Config.ARGB_8888);
Canvas canvas = new Canvas(output);
final int color = 0xff424242;
final Rect rect = new Rect(0, 0, bitmap.getWidth(), bitmap.getHeight());
paint.setAntiAlias(true);
canvas.drawColor(Color.TRANSPARENT);
paint.setColor(color);
int x = bitmap.getWidth();
canvas.drawCircle(x / 2, x / 2, x / 2, paint);
paint.setXfermode(new PorterDuffXfermode(Mode.SRC_IN));
canvas.drawBitmap(bitmap, rect, rect, paint);
return output;
} 4、设置画笔Paint的Shader，然后用该画笔绘制圆形图片
该方法是Glide和picasso使用的方法，用法简单便捷，占内占有率处于中等水平。
@Override
protected void onDraw(Canvas canvas) {
Drawable drawable = getDrawable();
if (null != drawable) {
Bitmap bitmap = ((BitmapDrawable) drawable).getBitmap();
Bitmap b = transform(bitmap);
final Rect rectSrc = new Rect(0, 0, b.getWidth(), b.getHeight());
final Rect rectDest = new Rect(0,0,getWidth(),getHeight());
paint.reset();
canvas.drawBitmap(b, rectSrc, rectDest, paint);
} else {
super.onDraw(canvas);
}
}
public Bitmap transform(Bitmap source) {
int size = Math.min(source.getWidth(), source.getHeight());
int x = (source.getWidth() - size) / 2;
int y = (source.getHeight() - size) / 2;
Bitmap squaredBitmap = Bitmap.createBitmap(source, x, y, size, size);
if (squaredBitmap != source) {
source.recycle();
}
Bitmap bitmap = Bitmap.createBitmap(size, size, source.getConfig());
Canvas canvas = new Canvas(bitmap);
Paint paint = new Paint();
BitmapShader shader = new BitmapShader(squaredBitmap,
BitmapShader.TileMode.CLAMP, BitmapShader.TileMode.CLAMP);
float mScale = (mRadius * 2.0f) / Math.min(bitmap.getHeight(), bitmap.getWidth());
Matrix matrix = new Matrix();
matrix.setScale(mScale, mScale);
bitmapShader.setLocalMatrix(matrix);
paint.setShader(shader);
paint.setAntiAlias(true);
float r = size / 2f;
canvas.drawCircle(r, r, r, paint);
squaredBitmap.recycle();
return bitmap;
}
5、修改像素
该方法无法支持抗锯齿，并且不支持Bitmap.Config.HARDWARE格式的bitmap，但用法简单，内存占有率同样处于比较低。
public class CircleImageView extends AppCompatImageView {
public CircleImageView(Context context) {
this(context,null);
}
public CircleImageView(Context context, AttributeSet attrs) {
this(context, attrs,0);
}
public CircleImageView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
@Override
public void onDraw(Canvas canvas) {
int width = getWidth();
int height = getHeight();
int minSize = Math.min(width,height)/2;
Drawable drawable = getDrawable();
if(drawable!=null && minSize!=0) {
if(Math.min(drawable.getIntrinsicWidth(),drawable.getIntrinsicHeight())==0) {
return;
}
int intrinsicWidth = drawable.getIntrinsicWidth();
int intrinsicHeight = drawable.getIntrinsicHeight();
float R = Math.min(intrinsicWidth, intrinsicHeight) / 2;
Bitmap bmp = transformBitmap(drawable, intrinsicWidth, intrinsicHeight, R);
Matrix imageMatrix = getImageMatrix();
if((imageMatrix==null || imageMatrix.isIdentity()) && getPaddingTop()==0 && getPaddingLeft()==0){
drawCircleImage(canvas, bmp);
}else {
if (imageMatrix != null && !imageMatrix.isIdentity()) {
canvas.concat(imageMatrix);
}
final int saveCount = canvas.getSaveCount();
canvas.save();
if (getCropToPadding()) {
final int scrollX = getScrollX();
final int scrollY = getScrollY();
canvas.clipRect(scrollX + getPaddingLeft(), scrollY + getPaddingTop(),
scrollX + getRight() - getLeft() - getPaddingRight(),
scrollY + getBottom() - getTop() - getPaddingBottom());
}
canvas.translate(getPaddingLeft(), getPaddingTop());
drawCircleImage(canvas, bmp);
canvas.restoreToCount(saveCount);
}
if(bmp!=null && !bmp.isRecycled()) {
bmp.recycle();
}
}else{
super.onDraw(canvas);
}
}
private void drawCircleImage(Canvas canvas, Bitmap bmp) {
try {
DrawFilter drawFilter = canvas.getDrawFilter();
canvas.setDrawFilter(new PaintFlagsDrawFilter(0, Paint.ANTI_ALIAS_FLAG | Paint.FILTER_BITMAP_FLAG));
canvas.drawBitmap(bmp, 0, 0, null);
canvas.setDrawFilter(drawFilter);
}catch (Exception e){
e.printStackTrace();
return;
}
}
@NonNull
private Bitmap transformBitmap(Drawable drawable, int intrinsicWidth, int intrinsicHeight, float r) {
Bitmap bmp = Bitmap.createBitmap(intrinsicWidth, intrinsicHeight, Bitmap.Config.ARGB_8888);
Canvas targetCanvas = new Canvas(bmp);
try {
drawable.draw(targetCanvas);
for (int y = 0; y < intrinsicHeight; y++) {
for (int x = 0; x < intrinsicWidth; x++) {
if ((Math.pow(x - intrinsicWidth / 2, 2) + Math.pow(y - intrinsicHeight / 2, 2)) <= Math.pow(r, 2)) {
continue;
}
bmp.setPixel(x, y, Color.TRANSPARENT);
}
}
}catch (Exception e){
NCFLog.e("transformBitmap","e="+e.getLocalizedMessage());
e.printStackTrace();
}
return bmp;
}
public boolean isHardware(Bitmap sourceBitmap){
if(sourceBitmap==null) return false;
if(Build.VERSION.SDK_INT>=Build.VERSION_CODES.O) {
return sourceBitmap.getConfig() == Bitmap.Config.HARDWARE;
}
return false;
}
}
来源：oschina
链接：https://my.oschina.net/u/2256215/blog/3036297