line-offset makes the tile borders visible

Context

Trying to style a layer using line-offset and the tiles borders become visible as a side effect

Steps to Reproduce

1. Create a map from a polygon dataset or from scratch with an empty layer, and then draw a polygon by hand
2. Style the layer with an extra border with Npx offset as

#layer {
  polygon-fill: #374c70;
  polygon-opacity: 0;
  line-width: 2;
  line-color:red;
  line-opacity: 1;
}
#layer::2 {
  polygon-fill: #374c70;
  polygon-opacity: 0;
  line-width: 2;
  line-color: blue;
  line-opacity: 1;
  line-offset:-3;
}

Current Result

red lines: actual polygon border blue lines: polygon border with offset

• If offset is < 0: the tiles that intersect my polygon has visible borders inside the polygon

• If offset = 0: Behavior as expected

• if offset > 0: the tiles that intersect my polygon has visible borders outside the polygon

Expected result

Just no tiles borders 😃

Browser and version

Any

.carto file

test_offset.carto.zip

Additional info

Please add any information of interest here below

[Algunenano]

Yeah, it’s not related to #14124. I’m keeping this open until the fix is released and installed in production.

Well, it’s only taken me ~13~ 15 months but it’s now in production.

[rafatower]

Indeed my intuition was correct, reverting that change fixes the bug:

• mapnik v3.0.15-carto branch:

• mapnik revert_offset_converter_fix branch:

(the slight change in style is just to avoid caching between tests)

but it breaks other things (see the polygon vertex and the many visual tests broken).

Fixing this would require some c++ & mapnik expertise, finesse keeping the good parts and amending the bad ones, and some extra test for it.