Linear feature end points at tile boundaries

[pramsey]

This is a bit of a corner case, but. When rendering linear features with distinct end-point rendering styles (a symbol at the end, or a dumbell or something) there is no way in the current spec to distinguish between a line that ends at a tile boundary, and one that is carried over the tile boundary by another line in the neighboring tile.

[hallahan]

Specifically flagging a vertex exactly at the edge of a vector tile as a clipped point would be helpful, because this would also allow the ability to draw the clipped edge along the tile by simply drawing a line from one clip vertex to the next.

[kkaefer]

@pramsey You are assuming that features in a vector tile are clipped, which is up to the user to do, but not something that the tile format defines (in fact, you can have features that are entirely outside of the viewport/extent of the tile).

At Mapbox, we are clipping features at a small buffer around the tile, so that lines that extent beyond the viewport /actually/ extent beyond the viewport and get clipped at render time.

[strk]

Same applies to areas. Distinguishing real polygon boundary from the product of clipping would be helpful. Could maybe be an additional command to change the "role" of a segment ?