questions about features/maintenance...

[farfromrefug]

Hi,

I am very intersted about your fork of tangram.
I am an app developper and maintain my own mobile app https://github.com/Akylas/alpimaps. It uses Nativescript for the app framework and my fork of carto mobile sdk https://github.com/Akylas/mobile-sdk for the map framework.
I am always considering switching map framework as maintaining my own is pretty tough. Yours seems really promising.
I have a few questions:

• do you plan on maintaining this in the future?
• do you plan on adding new features? Like clustering for example?
• do you have the android or ios doc ? it is a 404 on trangram website, and i would like to read it to see what's possible. For example i am wondering if layers can be "merged". For example i have separated mbtiles for map, contours, routes and i would like to merge them while rendering so that contour lines appear above ground layers but under roads. I also have a separated raster mbtiles for hillshading and i would like to render it in between layers just like contour lines.
• in carto i have a custom layer type which takes my rgb elevation raster mbtiles and use it to render slopes grade color using a shader. Would that be possible with your framework?
• with the yaml style is it possible to have app variable passed on and used in the style? For example to render differently a vector item which is "selected"

If all seems good on my side, i am more than willling to start contributing to your framework.

Thanks

[pbsurf]

Hi,

Very cool app! Regarding your questions:

• I do plan to maintain tangram-ng ...
• ... including adding new features, although I want to keep it as simple and lightweight as possible, so I'd probably add most of the logic for something like clustering to Ascend instead of tangram-ng
• The tangram-es Android and iOS API docs seem to work, although the walkthroughs are broken as you found. I don't use any of that code in Ascend and would basically consider it deprecated in tangram-ng. I'm open to updating or replacing it.
• Yes, actually the same is done for slope angle shading in Ascend - see hillshade.yaml and slope-angle.yaml at https://github.com/styluslabs/maps/tree/master/assets/scenes
• Yes, app variables can be used in the style, but tiles must be rebuilt for changes to take effect. This is pretty fast, so support for dynamic updates isn't a huge priority for me. For an example, see is_selected_fn in https://github.com/styluslabs/maps/blob/master/assets/scenes/stylus-osm.yaml#L282

I'd be happy to accept and help with contributions. For new features and major changes, please discuss before putting in too much effort since I want to keep tangram-ng lightweight and focused just on map rendering.

Best,
Matt

[farfromrefug]

@pbsurf thanks a lot for your detailed answer. I am deeply interested in your work and tangram-es. Could really replace my current framework. I have forked and already made a few changes https://github.com/farfromrefug/tangram-ng. Will create PR when i can.
Talking about PR i saw a few PR on tangram-es i am really interested about:

• [wip] postprocess shader tangrams/tangram-es#1605: post processing could be interesting. I am wondering if something like this could be possible
• Add support for multiple mbtiles tangrams/tangram-es#2111. My app uses multiple mbtiles separated by regions. I am even thinking about having a server with per region mbtiles like organic maps.
• Tile fallback tangrams/tangram-es#2120: this is a must have for me.
• Fix label collider tile scale tangrams/tangram-es#2142: related to the one above
• Added methods to TouchInput.LongPressResponder for long press + pan, and long press up. tangrams/tangram-es#924: may users expect this today
• Add support for updating and deleting MapData features tangrams/tangram-es#2112 : maybe ?

Would you be willing to integrate them?

[pbsurf]

I'm not sure how many of the open tangram-es PRs could be merged easily given all the changes I've made - here are some quick thoughts for each:

• adding an optional post-processing pass sounds good; actually creating an effect like your example is on my TODO list for Ascend (but just with the regular hillshading shader, not postprocessing).
• In Ascend, multiple mbtiles are imported into a single mbtiles files, so that multiple DB queries aren't needed to find a tile. One thing I'd be open to is adding support for passing custom SQL to MBTilesDataSource so that it would be possible to attach multiple mbtiles files to the DB connection and then create an sqlite view using UNION to allow querying all mbtiles as if they were a single database.
• How would you need tile fallback to work? Do you need it because you have a tile source where the maximum available zoom depends on location? I have been planning some kind of option to always request tiles covering the current view at some zoom level (e.g. z=13) if the current zoom level is higher.
• If there was an issue w/ tile scale in LabelCollider, I may have already fixed it (if not, I will).
• I haven't worked on the Android or iOS code in Tangram, but if you test the changes, I'd be happy to accept the PR.
• In tangram-ng, ClientDataSource has been modified to return an id for added features, which can be used to replace the feature (replacing with an empty feature can be used to effectively delete). Will this work for you?

[farfromrefug]

@pbsurf yes i test everything on android and will do the same on ios. might be even more platforms in the future

• great for the peak finder ! postprocessing is necessary to render the horizon lines of the summits. This is what makes it really nice
• for the mbtiles I am starting to thing I could create new data sources deciding between multiple entry data sources, like i do in carto SDK. i have a few like merge, or, ... what you propose would be the equivalent of the merge ? i mean make it like if it was one tiles containing the content of both tiles (queried from 2 mbtiles)? for example in carto I merge main mbtiles with contours mbtiles to show contours in between layers (land cover and roads)
• tile fallback is for mbtiles which have a minzoom of 12 and you still want to show them at zoom below 12. a example is hill shade. i generate tiles starting at zoom around 9 or 10 to reduce tile size but still want to render them starting at zoom 5. this is what i do in carto.

there are many features I need to investigate in tangram to see if they are possible and if not, if they are doable.

a few that comes to mind right now:

• capturing current view to image
• offsetting center position by screen size. useful in navigation mode to make the center be lower or higher on the screen
• padding so that when you fly to a BBox it does by making so the BBox is visible in a padded region of the screen (useful when you have bottomsheet or other ui components are visible)
• querying features by regexp or search in tiles (limiting min and Max zoom levels)
• reading hill shade tiles to read elevations. i create elevations profiles using this technique in carto
• maybe per layer vector tile element click/longpress listeners
• will think of more

[pbsurf]

Multiple layers can be merged/combined, with ordering controlled by the order and blend_order parameters - see https://tangrams.readthedocs.io/

If the min and max tile zooms don't vary by location, then there is no problem - the min and max is just set in the Tangram source configuration and the min is used for all lower zoom levels and the max for all higher zoom levels

Regarding the other features:

• capturing the current view to an image can be done with glReadPixels()
• offsetting center/padding: see setPadding() and getEnclosingCameraPosition() in map.h
• querying: Tangram doesn't retain the decoded feature information once it has created the tile for display. I think search would be better implemented separately from Tangram.
• Yes, elevation tiles are read directly in Ascend - see MapsApp::getElevation() at https://github.com/styluslabs/maps/blob/master/app/src/mapsapp.cpp#L1167

[farfromrefug]

@pbsurf working a bit on tangram-ng and bringing it back to ios/android as a framework/library. All good for android but on ios i have build issues. I updated the build scripts a bit with your changes farfromrefug@d663e4d but i got a link issue. fontstash symbols are not found:

"_fonsSetSize", referenced from:
      Tangram::FontContext::layoutLine(Tangram::TextStyle::Parameters&, float, float, char const*, char const*, std::__1::vector<Tangram::GlyphQuad, std::__1::allocator<Tangram::GlyphQuad>>&) in libtangram-core.a[70](fontContext.o)
      Tangram::FontContext::layoutMultiline(Tangram::TextStyle::Parameters&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>> const&, Tangram::TextLabelProperty::Align, std::__1::vector<Tangram::GlyphQuad, std::__1::allocator<Tangram::GlyphQuad>>&) in libtangram-core.a[70](fontContext.o)

what i dont get is that fontstash.h is added as include in the core CMakeLists. Do you have an idea?

EDIT: i actually fixed the build. I had to apply changes you made to the android version
EDIT2: so i get the ios demo app to run but i dont see anything. I get region changed events and i see the map is moving . But nothing is "drawn".
I also add to fix some gl shader versions from 300 to 330. I had unsupported version errors.

Do you think you can help?
EDIT3: ios framework is now fully working!