Bring back a representation of layers

[sophiedeziel]

Part of #221

There is value into getting a representation of layers like we had before. I brought back the class. The reason is that its is very well suited to hold some information like layer height.

I exposed the layer count as a getter instead of exposing layers themselves. It is an essential affordance for library clients to implement some sort of slider to inspect the inner layers using single layer mode and/or min/max layers.

I had to slightly change it just to replace GCommands by Paths.

[sophiedeziel]

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• Bring back a representation of layers #233 👈
• v3 temporary branch #225 : 5 other dependent PRs (#220 , #224 , #227 and 2 others)
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Visit the preview URL for this PR (updated for commit e4442eb):

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[remcoder]

How will we handle a gcode file that is incrementally fed to the preview, like when used as a realitime progress of an actual print?

[sophiedeziel]

It will handle it pretty well actually! As long as the same job object is used and appended paths on top of, they will be indexed on the right layer.

Layers are no longer used in the rendering logic (yet), it's a convenience for lib clients. I have plans for the layer height to be calculated from movement and used for the geometries.

To officially support incremental rendering, some logic has to be added to pop back the last path into the current path in case it was not finished. It's reference in the layer is kept. After that, rendering will just work

[sophiedeziel]

I made the changes to make sure progressive rendering works gracefully in all cases

[sophiedeziel]

Turns out layers are already useful with their z and height attributes!

#234