Retract only when crossing perimeters

Slic3r has a feature named "retract only when crossing perimeters" that stops retraction when the print head is moving solely within the object. In general this is a good idea, but there is a flaw in the implementation. The flaw is that it also causes no retraction to be done on the bottom layer. When on the bottom layer, and traveling from perimeter to perimeter within the object, you are still on the exterior of the object.

So this feature should not apply to the bottom layer. It should just follow the normal retraction configuration, and only apply this above this level.

Why is it ever a good idea? With no retract you loose plastic during the move so the next filament doesn't start properly.

---

[www.hydraraptor.blogspot.com]

That's a good point. I though it would be advantageous to not have the extruder motor rapidly going back and forth while you were within an objects walls. I actually have retraction on mine set all the time.

I started thinking about this when I observed Cura's behavior. By default (at least in my case) Cura has a feature called "Retraction combing" turned on. With this feature turned on, whenever it can, it stays within an objects perimeter and does not retract. And this is not just for straight-line moves. Cura will take a circuitous path to get from point A to point B so that it doesn't cross perimeters and, therefore, doesn't need to retract. This feature too is flawed for the same reason - on layer 0, it may be staying within the object's perimeter, but it is actually on the outside of the object. I have this feature turned off.