In Spine, we can apply a "Mesh" to the image. This is actually a masking method. Imagine you are making an eye in Photoshop, we create two circles, one for the black of the pupil and the other for the white of the eye. To move the pupil, we mask inside the white circle and move the pupil around. So we can move the pupil (black circle) inside the circle without leaving the white circle. This is done with weights in Spine and it happens with perspective. This is a very tedious process... Is there a masking system like in Photoshop where we can move within the "Mesh" borders? Or will there be an update to Spine regarding masking?
Will there be an update to Spine regarding Masking in Animation?
Currently, Spine does not support a masking system similar to Photoshop's, where you can move elements within a defined mask area. The existing masking functionality in Spine is primarily through the use of clipping, which is a more complex and runtime-expensive operation. Clipping in Spine is limited to polygonal shapes and does not support feathered edges or more advanced masking techniques like those found in Photoshop. While there have been requests for more advanced masking features, such as feathered masks or alpha-based masking, these are not yet implemented due to technical limitations and the focus on features that work across various game engines. There is no specific timeline for when or if such features will be added to Spine.
To add to Spinebot's answer, at least for your specific example, you'd usually do an eyeball not by using a single image as a mesh and moving the pupil pixels, but by having transparent eye holes, then place the pupil behind it -- no weights.
You can't always place an image on top to hide things. In that case you can use clipping to hide them. While this does have a hard edge, sometimes that can be overcome by placing an image on top of the clipping edge.
More advanced clipping has great uses, but also some technological challenges. We are always working on improving Spine, though new clipping features aren't on our short term radar.