The only shader of any real significance is the one which allows the shields to appear destructible.
A script gives the shader the positions of all collision points (points where the lasers hit the shield). The shader doesn't draw fragments within a certain radius of each point. The script also keeps a list of these points so it knows which parts of the shield have been destroyed. This allows the lasers to pass through the missing parts of the shields.
Below is the relevant portion of the shader code.
