Overlays support

Goal

Support overlays like the ones you can create from the CartoDB editor (title, lon/lat annotation, anchored text item, anchored image) so it is possible to generate static images with them on top of the map.

Open questions

• markdown or html support?
• only available for static images?

Alternatives

HTML5 Canvas

• basic font rendering + metrics
• transpiler: markdown/html to components
• plug it into coordinate system, cut for several tiles
• hard to implement
• easy to integrate as another renderer

Flipboard's canvas-react

• text rendering supported, check how much of it
• transpiler: markdown/html to components
• probably a lot of issues with spacing and text metrics already solved
• plug it into coordinate system, cut for several tiles
• hard to implement
• easy to integrate, it should be as it is still canvas

Mapnik font rendering

• fake inline geojson data + font styling (so it does not require db conn)
• limited in styling
• no effort to integrate it in tiles
• easy to integrate
• easy to implement

Phanton JS

• best rendering support, straight away: it's a headless webkit
• plug it into coordinate system, cut for several tiles
• probably it makes sense to be a separate service (not ideal) that only returns images for test+style, because I'm against introducing phantom overhead in windshaft
• easy to implement
• hard to integrate

Mapnik + Any canvas/image solution

• leverage font rendering to a more powerful approach: like phantomjs
• use mapnik to get images as marker files into the appropriate tiles
• hard to implement, it requires implementing two components
• hard to integrate, images must be managed/cached (integrate with grainstore?)

html2canvas

• really difficult to run server side: no support for nodejs
• easy to implement?
• hard to integrate