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