Skiasharp performs under a low dpi in Android

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I use avalonia to achieve cross-platform. Because avalonia has native controls like ShiaSharp.Views.xxx, i have to create my custom control.
SKCanvas can not render on subpixel and it performs so bad in Android.
dpi of my phone is about 260, but measured by a real ruler, dpi of skcanvas is about 90
"-20" is rendered by my custom control, and "s" is rendered by avalonia control.
Actually this problem also occurs in Windows, just not so obvious.
I guess that there is a buffer (maybe skbitmap) created, and its clarity depends on the size of the buffer.