render.OverrideBlendFunc leaves black color on edges where must be alpha

[LisyFOX]

https://files.facepunch.com/forum/upload/135013/f6b0d03b-d21b-4fcf-8ef0-54554ae09cee/image.png
Hi, I'm tried many methods, but it's not brought me any result to fix it. I have minimap and mask and I'm blending it for get blurred edges of minimap, but blending leaves black color on edges there are must be alpha channel, but it's not there. So first screenshot with using render.Clear(0,0,0,255) and second without.

https://files.facepunch.com/forum/upload/135013/f6b0d03b-d21b-4fcf-8ef0-54554ae09cee/image.png

https://files.facepunch.com/forum/upload/135013/2412d121-007b-4aa5-b9af-24ac2d37f541/image.png

[LisyFOX]

I've found Blue's Masks and Shadows! and It's works fine! Thanks him for it! And thread can be closed.