NOTES.cutouts

Notes on implementing the PCB noundary and cutouts:
---------------------------------------------------

I. Step 1 processing:
    KiCad arcs, lines, and circles must be converted
    to sets of bounds:
    a. main boundary
    b. drill holes and other circular cutouts
    c. internal cutouts

II. Step 2 processing:
    a. Circular holes must be checked against the main
    outline and the main outline's segments adjusted
    accordingly.
        + there may be only 0 or 2 intersections with
          the main boundary; 1 intersection means the
          hole is tangent to an edge and this is
          forbidden since it is a serious mechanical
          defect. More than 2 intersections is forbidden
          since that would split the main outline into
          multiple bodies.

          There is an exception to this rule when the
          intersection happens to be the terminal point
          of a segment; in this instance we need to
          store a pointer to both entities (CW entity
          first) and (to avoid duplicate calcs in the
          future) mark whether the intersection is a
          terminal point or not.

        + Take any of the arcs formed by the split at
          the 2 intersections and determine if it is
          inside or outside the main outline. If it is
          outside then take the CW terminus and split
          the intersecting entities as necessary,
          otherwise take the CCW terminus and split
          the intersecting entitites. Finally, eliminate
          all intermediate segments in the outline in a
          CCW direction. Remember to correctly handle
          the cases where the ends of the segment list
          are involved.

    b. Circular holes must be checked against each cutout
    and the cutout adjusted accordingly.
        + [TBD] the scheme is similar to that of the
          main outline but we are performing a boolean
          addition rather than a subtraction
        + ???

III. Step 3 processing:
    Remaining circular holes must be checked against
    eachother and overlapping holes merged; to avoid
    multiple calculations, create lists with all holes
    which overlap. In a pathological case for example
    a user may employ multiple holes to represent a slot
    and these holes must be amalgamated to produce a
    strange undulating slot. Since we cannot guess at
    the user's intention, such multiple drills will
    remain as multiple overlapping drills; they will not
    be interpreted as a slot.

IV. Step 4 processing:
    Cutouts must be checked against eachother and
    merged.

    a. [TBD] this requires a bit more thought than the
    case of circles being removed since in many cases
    we will be dealing with multiple segments.

V. Step 5 processing:
    Cutouts (except for merged circular holes) must be
    checked against the main outline and the outline
    adjusted accordingly.

    a. [TBD] The processing shall be similar to that
    of Step 4 but we are performing a boolean subtraction
    rather than an addition.