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Re-implement "avoid edges" for static map tile generation #12461
Description
When we implemented global collision detection (#10436), we removed the per-tile implementation of the symbol-avoid-edges style property because it was no longer necessary -- global collision detection handled the tile boundaries. For static tile generation, we relied on running "global" collision detection on the tile including the symbols in its buffers, in order to handle collisions at the boundary.
That approach works for point labels, but it can break down with line labels because the anchors can get placed at different locations in neighboring tiles. I don't know how common this will actually be in practice, but in theory it will cause more bad label clipping at tile boundaries in api-gl.
I think to implement this we'd project the tile boundaries into viewport space and then do a check against that bounding geometry before we tried testing the line label against the rest of the collision index.
/cc @ansis @jfirebaugh @ian29
Activity
ChrisLoer commentedon Jul 27, 2018
I spent some time looking at one of our core navigation styles using an updated version of api-gl. My impressions were:
It occurs to me that since this only matters for api-gl, we could even get away with skipping most of the logic necessary for handling off-axis (e.g pitched) tile boundaries.
My gut right now is that this is small-medium fix difficulty and small-medium priority -- i'm going to drop it off my immediate todo list, but anyone with more perspective feel free to bump it back up.
cc @lilykaiser
lilykaiser commentedon Jul 30, 2018
Misread this 🤦♀️ I will unassign you
ChrisLoer commentedon Jul 30, 2018
I looked through a bunch of mapbox core styles, and we barely use
symbol-avoid-edgesin them -- and not at all in for instancestreets-v10. Also, as far as I can tell from looking at the old implementation (pre-global collision detection), we never defaulted line labels to avoid edges (See old behavior at calls toplaceFeaturein https://github.com/mapbox/mapbox-gl-native/blob/18d735ccc20e1e7d4616b3d3b5b1a527a01d1b91/src/mbgl/layout/symbol_layout.cpp). So we would have had these problems before too.We should still re-implement support for
symbol-avoid-edgesin the tiled map case just so we support styles that do use it, but unless I'm missing something we've already been living with the line-clipping issues.As part of re-implementing
symbol-avoid-edges, maybe it makes sense to make the default for line layers betrue? The overall effect would be something like:[core, node] Re-implement "avoid edges" behavior for MapMode::Tile
[core, node] Re-implement "avoid edges" behavior for MapMode::Tile
[core, node] Re-implement "avoid edges" behavior for MapMode::Tile
ChrisLoer commentedon Aug 20, 2018
Fixed in #12520.