Dense infill under solid layer

left	right
feature activated	without

6% infill

When this switch is activated, if the infill% is under 40%, it search a supported area under each solid surface, with only straight lines between perimeters. When it find one, it use a special infill process that lay a perimeter (with overlap, so it's ~supported by the current internal perimeter and then a 42% rectilinear infill inside it. This will prevent any curling that may ruin your top surface, and ensure everything can be supported even with an infill ratio of 0%

note: beta feature, not yet in the release package. It will replace the manual dense infill.