How to 'crop' a g-code

[paulus.v]

I don't think you realise just how complex a mathematical problem what you're asking for constitutes, it would need to

I do not see where it is the complexity. My g-code is a list of points defined by XYZ. I need to look at the the XY coord. of every line and compare with my shape. If the point is inside the shape keep the line, if it is outside delete it. That simple.

To get an idea of what I'm doing, I have the shapes already cutout and I'm applying a surface texture on them. I need to eliminate the extra movement, cutting out air, around the shape.