How to apply mask softness only on one side of the mask?

[Sanster]

Hi, thank you for your outstanding work. I am adding an outpainting function in my open-source project and have a question to ask: How can I modify the soften_mask function to make it only apply "soft" to one side of the mask?

https://github.com/parlance-zz/g-diffuser-bot/blob/a003394476cb5495d1705daa013b94829a57c121/modules/g_diffuser_lib.py#L392

This is the current effect, if I only want to outpaint one side, the bottom mask will also be soft.

image	mask