In earlier versions, clippings could not be made on a hard fill,
but from DCL ver.5, clippings can be made on hard fill in a way similar to a soft fill.
In other words, the clipping of the tone pattern is not performed by the hardware.
Instead, boundary points specifying the overlap in the specified region and the clipping range
and the data are handed over to the tone routine.
The algorithm for calculating this clipped boundary line
runs on the precondition that the direction of the boundary line is known.
Here, the direction of the boundary line is the clockwise or counter-clockwise direction
in which the sequence of points defining the boundary is specified.
Although this algorithm has poor compatibility with traditional rules for fill tone patterns,
it was created nonetheless since the direction of the boundary line on the map (TC)
must be provided to determine the outside and inside of the boundary.
The actual procedure of tone clipping is as follows.
Therefore, it is dangerous to perform clipping when filling in a polygon with overlapping boundaries. To be on the safe side, the user is advised to
When you wish to fill the outside of a polygon, divide the area into 2 sections so that the polygon will definitely be be clipped, reset the clipping area (viewport), and call the tone routine twice.