Android应用中绘制圆形头像的方法解析

要画这种圆形带阴影的头像，个人分解成三个图层

1,先画头像边缘的渐变

RadialGradient gradient = new RadialGradient(j/2,k/2,j/2,new int[]{0xff5d5d5d,0xff5d5d5d,0x00ffffff},new float[]{0.f,0.8f,1.0f}, Shader.TileMode.CLAMP);
paint.setShader(gradient);
canvas.drawCircle(j/2,k/2,j/2,paint);

2,截去出圆形头像Bitmap

/**
 * 转换图片成圆形
 * @param bitmap 传入Bitmap对象
 * @return
 */
 public Bitmap toRoundBitmap(Bitmap bitmap)
 {
  int width = bitmap.getWidth();
  int height = bitmap.getHeight();
  float roundPx;
  float left,top,right,bottom,dst_left,dst_top,dst_right,dst_bottom;
  if (width <= height) {
   roundPx = width / 2 -5;
   top = 0;
   bottom = width;
   left = 0;
   right = width;
   height = width;
   dst_left = 0;
   dst_top = 0;
   dst_right = width;
   dst_bottom = width;
  } else {
   roundPx = height / 2 -5;
   float clip = (width - height) / 2;
   left = clip;
   right = width - clip;
   top = 0;
   bottom = height;
   width = height;
   dst_left = 0;
   dst_top = 0;
   dst_right = height;
   dst_bottom = height;
  }

  Bitmap output = Bitmap.createBitmap(width,
    height, Bitmap.Config.ARGB_8888);
  Canvas canvas = new Canvas(output);

  final int color = 0xff424242;
  final Paint paint = new Paint();
  final Rect src = new Rect((int)left, (int)top, (int)right, (int)bottom);
  final Rect dst = new Rect((int)dst_left, (int)dst_top, (int)dst_right, (int)dst_bottom);
  final RectF rectF = new RectF(dst_left+15, dst_top+15, dst_right-20, dst_bottom-20);

  paint.setAntiAlias(true);

  canvas.drawARGB(0, 0, 0, 0);
  paint.setColor(color);

  canvas.drawRoundRect(rectF, roundPx, roundPx, paint);

  paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
  canvas.drawBitmap(bitmap, src, dst, paint);
  return output;
 }

3,最后画上白边

Paint paint = new Paint();
   paint.setColor(0xffffffff);
   paint.setStrokeWidth(10);
   paint.setStyle(Paint.Style.STROKE);

   canvas.drawCircle(j/2,k/2,j/2-20,paint);

PS：Android App常用图标尺寸规范
1. 程序启动图标：
LDPI (Low Density Screen，120 DPI)，其图标大小为 36 x 36 px。
MDPI (Medium Density Screen, 160 DPI)，其图标大小为 48 x 48 px。
HDPI (High Density Screen, 240 DPI)，其图标大小为 72 x 72 px。
xhdpi (Extra-high density screen, 320 DPI)，其图标大小为 96 x 96 px。
xxhdpi（xx-high density screen, 480 DPI）,其图标大小为144 x 144 px。

2.底部菜单图标
（1）大屏:
完整图片（红色）: 72 x 72 px
图标（蓝色）: 48 x 48 px
图标外边框（粉色）: 44 x 44 px

（2）中屏:
完整图片: 48 x 48 px
图标: 32 x 32 px
图标外边框: 30 x 30 px

（3）小屏:
完整图片: 36 x 36 px
图标: 24 x 24 px
图标外边框: 22 x 22 px

3. 弹出对话框顶部图标

小屏 24 x 24 px Low density screen (ldpi)
中屏 32 x 32 px Medium density screen (mdpi)
大屏 48 x 48 px High density screen (hdpi)

4. 长列表内部列表项图标

小屏 24 x 24 px Low density screen (ldpi)
中屏 32 x 32 px Medium density screen (mdpi)
大屏 48 x 48 px High density screen (hdpi)

5. 底部或顶部tab标签图标

（1）大屏 (hdpi) screens:
完整图片（红色）: 48 x 48 px
图标（蓝色）: 42 x 42 px

（2）中屏 (mdpi) screens:
完整图片: 32 x 32 px
图标: 28 x 28 px

（3）小屏(ldpi) screens:
完整图片: 24 x 24 px
图标: 22 x 22 px

6. 底部状态栏图标

ldpi (120 dpi) 18 x 18 px 小屏
mdpi (160 dpi) 24 x 24 px 中屏
hdpi (240 dpi) 36 x 36 px 大屏
xhdpi (320 dpi) 48 x 48 px 特大屏