* Change: In Cumulus/plugins.block.spares, allow the QuadTree to have
only *some* of it's four childs (BL, TL, TR, BR).
Modify QuandTree.getLeafUnder() so when there is no leaf under
the point, due to an incomplete tree, we get the closer leaf.
Leaf are suppressed when their center points (where the buffers
are to be put) are under a FIXED Instance (that is, an opaque block).
Those opaque blocks (or macro blocks) must be put *on the periphery*
of the design, because the closer they got to the center, the larger
the chunks of QuadTree that are removeds.
* Change: In Cumulus/plugins.block.clocktree, based on the spare
QuadTree changes, can now build a clock-tree with some of the
leaf missing. Should find a way to compensate for the missing
leaf wires & buffer (dummies).
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