Shattered Mirror Cracks

This post currently has placeholder images and videos. I’m just waiting on the green light from PlaySide to include the actual media I’d like to share.

At PlaySide I worked on Shattered (Unity - Quest 3 Mixed Reality)

One of my tasks was to make cracks grow on a mirror, eventually transitioning into shards falling out.

Depending on the situation, the crack needed to either:

• Split the mirror in half first, then grow outward
• Or grow evenly in all directions from the center

To achieve this, I created a custom mesh in Blender by tracing the glass shards that would fall out.

I tried two techniques to animate the crack, and ended up going with the second:

Technique 1 - Distance-based reveal

I used a float parameter in the shader to control how much of the crack was visible, based on distance from the center. When needed, I added a bias to the Y-axis to grow the central split first.

While this was easy to set up, it didn’t look convincing:

• It was obvious the crack was simply being revealed by distance

• Pieces of the crack would appear before they were actually connected to the main split

Technique 2 - Vertex color-based reveal

In this approach, the shader reveals the crack based on vertex color.

I wrote a Blender script that starts from a selected vertex and performs a flood fill across the crack mesh, assigning weights to each vertex as it spreads outward. These weights are normalized and stored as vertex colors.

For the split crack effect, I updated the script to handle a two-phase flood and created a group to store all the vertices that were part of the split.

With this setup, I could drive the animation with a 0–1 float value in the shader.

The result: both the cracks now grows in a much more natural way, and no disconnected pieces appear out of order.