Detail this asset from Unity Asset Store: Original Link
This is a paid asset, but now you can download Soft Mask Free.
Soft Mask v1.6 (Latest version)
Soft Mask v1.5
Soft Mask v1.3.1
Soft Mask is a UI component that masks child elements. It works almost like standard Unity’s UI Mask but supports gradients and semi-transparency.
Demo | Documentation | Support Thread
• Easy to use: just drop it on the Game Object in the same way as Unity’s standard Mask.
• Supports Image, RawImage, Sprite, Texture and RenderTexture.
• Works with TextMesh Pro.
• Supports inverted masks.
• Can be easily supported in your shaders.
• Fully real-time: create, destroy, enable, disable, move, rotate and reorder a mask and UI elements at runtime.
• Can restrict input processing to only visible parts of the masked UI.
• Adjustable mask sampling: use black and white images, images with transparency or set weight of each color channel manually.
It’s intended to use with Unity’s UI only. No Sprite or 3D support is included.