DEL and TRI

[mdsumner]

this is the relationship:

• DEL must be composed from edges, and edges can come from any model
• TRI must be composed from close paths, there's no path in SC, ARC or TRI
• DEL0 should exist, and be the default workhorse
• TRI cannot be set-vectorized, we have to call earcut for each POLYGON
• DEL is set-vectorized, classify all triangles by intersection with input paths (or holes)
• triangles in DEL that fall in holes are not visible, but don't need to be removed
• if we DEL a TRI we could test triangle inclusion to classify the triangles that are in holes

All up I think that makes a very compelling feature set, we can't TRI() a lot of things, but we can use a TRI to reclassify a better quality triangulation made only from the edges which should be easier and more efficient than the pfft thing - so we don't have to try keeping paths in all the workflows.

[mdsumner]

in vignette now