Grid Reverse Mask

I was wondering if it was possible to do a Reverse Mask on the Unity UI Image that is in a specific shape, like a grid? Similar to the image. I wanted to do it without using a second image as a mask. I wanted to do it somewhat dynamically.

 

yes, you can write an own shader.
As a starting point you can download the built in shaders: https://unity3d.com/get-unity/download/archive (select "Built in Shaders" from the left drop down).
In the downloaded zip file navigate to DefaultResourcesExtra -> UI.
Probably you should unpack the UI-Default.shader and modify it to fit your needs.