How the glass actually breaks
Each pane is a lattice of cells rather than a single object. An impact damages the cells nearest the contact point and the crack grows outward from there, which is why a second hit near the first one behaves differently from a hit on untouched glass. Crack Spread Width sets how far that damage reaches and Crack Raggedness controls how irregular the boundary is.
Depth is modelled separately from surface damage. Glass Layers gives the pane thickness, so a ball can remove the front layer and leave the rest standing. That is what produces the layered look where a wall becomes progressively more transparent before it finally opens.
Collapse is a separate event from shattering. When a section loses enough support it detaches as a group, which is why Hanging Support and Total Collapse Pieces exist alongside the per-hit shard settings.

