Render ways with both highway and railway tag

[matthijsmelissen]

Make sure that ways that have both a highway and a railway tag are rendered
both as highway and railway.

This resolves #874.

This assumes #866 and #884 are merged first.

Thanks to @kkofler.

[matthijsmelissen]

This is urgent as it resolves an important regression (railways on top of roads were not rendered).

[matthijsmelissen]

@pnorman Could you check the performance of this?

[matthijsmelissen]

It would also be good if some people could properly test this for potential newly introduced bugs.

[pnorman]

@pnorman Could you check the performance of this?

Checking fd1df07, then 40a747d. In future please indicate the commits you want me to compare, as it's not trivial for a PR that depends on other PRs.

[pnorman]

It's slower. With changes, 8.987 MT/s, without that last change, 9.021 MT/s, a decrease of 0.38%. This result is statistically significant. The slowdown seems distributed across all layers.

It's probably worth the slowdown. We've gained more speed in the last few months than we'll be losing here, including more speed from the roads refactorings which introduced this bug. Assigning to Andy.

It's worth noting that reusing the same layer for roads_fill and roads_casing would probably increase speed by far more than any loss here.

[matthijsmelissen]

It's worth noting that reusing the same layer for roads_fill and roads_casing would probably increase speed by far more than any loss here.

The problem with that is that highway-area-fill is still rendered in between these two layers. To merge roads_fill and roads_casing, we would need to merge the linear roads and areas SQL (for example with a union), which is probably undesirable.

[matthijsmelissen]

@gravitystorm Do you already know when you will have time for your next round of merges? I think there are quite a lot of people waiting for this fix.