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
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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);
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2,截去出圆形头像bitmap
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/**
* 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;
}
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3,最后画上白边
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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);
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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