line-cap image / vertex-first, vertex-last

[der-stefan]

User Story

I would like to render bridge abutments at the first and the last node of a line for OpenTopoMap.

Rationale

• Currently there is no direct way to place an image at the first and/or last node of a line. A workaround is to add points to the vector tile as nodes. However, that adds redundant information. Furthermore, the line-cap image should be rotated according to the angle of the connected line.
• Similarly, Mapnik introduced "vertex-first" and "vertex-last" due to our feature request in 2014: Missing linecap image for LineSymbolizer mapnik/mapnik#2122
• It could be considered as an extension of the option "line-cap": "sprite_image". However, it is preferable to be able to control independently like

"line-cap": "round";
"vertex-first": "sprite_image_1";
"vertex-last": "sprite_image_2";

• It could also be a cool feature to render a sprite image at every node or all but not the end nodes of a line. Syntax could be "vertex-all" and "vertex-inner". Instead of "vertex-*" the scheme could also be "node-*".

Impact

Impact is low, as it just enables a more professional styling for bridges. But there could be also other use-cases where you want to draw something at the end nodes of a line.

[HarelM]

Thanks for taking the time to open this feature request!
As far as I understand this request it is related to the style specification, which is shared between native and web.
I therefore suggest to open a new issue in the maplibre-style-spec repo and explain the suggested style spec changes.
This issue can be left open to track the implementation in maplibre-gl-js and a new issue should be open in native once the proposal is approved to track implementation there.
Thanks!