High Performance Map Interactions Using HTML5 Canvas | Hacker News Reader

High Performance Map Interactions Using HTML5 Canvas

chairnerd.seatgeek.com

177 pointsefkv25 comments

This is an awesome writeup!

I was playing with the demo linked elsewhere in this thread [demo], and noticed a bit of a hiccup when scrolling past multiple zoom levels. It seems like there'd be a bit of a pause as the tiles were rendered at each successive zoom level. It may be worthwhile to debounce the scroll event listeners with a small timeout, so you can catch multiple successive scroll events and zoom straight to the target zoom level without having to render each step along the way.

Quick video of the stuttering: http://gfycat.com/BrilliantActiveAfghanhound

[demo] https://seatgeek.com/senators-at-flyers-tickets/4-11-2015-ph...

Thanks!

This has been an issue we have struggled with for a while. What you are suggesting is basically how Leaflet typically handles scroll events. The issue, however, primarily lies with the Apple trackpad. Basically the Apple trackpad "fakes" inertial scrolling. When using the base Leaflet implementation, we would zoom straight to the target zoom level (great), but then the tail end of the intertial zoom would force it to zoom once more (bad).

For a normal map of the world that has like 20 or 30 zoom levels, accidentally missing the target zoom by a level does not matter too much. However, on our maps, with only a couple zoom levels, missing your target zoom level really hinders usability. Therefore we debounce the scroll events to keep zooming to a level at a time. So its not a matter of tile rendering blocking zoom, but rather a purposeful, if imperfect, decision.

This is by no means the right solution and we are keeping our eyes on the new Leaflet release that may help solve this. Great catch, btw.

If you are really interested, here is a thread on exactly this issue: https://github.com/Leaflet/Leaflet/issues/2154

Thanks for the thread. I figured mapping continuous input to discrete levels was more difficult than I was making it seem (especially with the fragmented way the web presents these devices).

No problem. It wouldn't be fun if it were easy!

@Developers, I'm sorry if I missed it in the article, but can I see the online demo somewhere? I went to your website and maps but still couldn't get to it. Thanks.

https://seatgeek.com/senators-at-flyers-tickets/4-11-2015-ph...

Tiles are good and responsive, but you may want to add a shadow behind the text "Section N, Row M" because some arena pictures are largely white!

Any chance we could get a screenshot of where you are seeing this? Or at least a venue/section? Thanks!

Great write up! I've been working with maps lately and this was a very interesting read.

I've tried the Leaflet SVG layer and it can become quite slow when loaded with thousands of points.

Another approach would be to use a custom SVG layer overlay using CSS Transforms. I've used an SVG overlay with D3 and it was much faster at panning and zooming. It could handle ~30k points (and lots of lines) without a problem on my laptop.

Edit + an example: http://i.imgur.com/ey8YDWJ.jpg

Canvas tiles are exactly the approach we took in making the ChromoZoom genome browser, where we wanted people to smoothly zoom in on client drawn data at 60fps through 10 orders of magnitude: http://chromozoom.org (Note that it's only used for user provided data, as the default tracks are prerendered, like Google maps v1.)

I highly recommend this hybrid approach of 10-20 canvases plus a sprinkling of HTML elements for anybody looking to maximize responsiveness in this type of UI. In our tests, SVG and HTML start stuttering in draggable layers around tens of thousands of elements (easier to hit than you'd think). We actually decided to do mouseover calculations ourselves, in a pixel map within a mousemove handler, since having separate elements to trigger the mouseover was too expensive.

Really great to have a case study like this for knowing when to use SVG/DOM or Canvas.

I knew that Canvas can easily be redrawn 60fps for things like games (though it may overheat your laptop). Didn't know about using them as shiftable tiles though. What a great way to minimize redraw! Is this how most online maps work?

Tiling is a very common technique for online maps. Image tiles used to be the standard, but there has been a lot of progress made with vector tiles (what the new Google Maps uses), mainly due to the huge improvements in browser performance as well as greater support of WebGL . Take a look at Mapbox GL, a very cool vector tile renderer:

https://www.mapbox.com/blog/mapbox-gl-js/

This is awesome, thanks for sharing!

One question, on your previous version you had a ton of big purple timeline bars. Were those mostly "recalculate styles" or "update layer trees"? I'm having similar issues and I'm wondering if canvas may be a better decision than DOM.

I am quite certain there was a mix of both, but I honestly cannot remember the details of the timeline. Basically, if your bottleneck is moving lots of DOM elements around, then clustering is a good next step (depending on your use case). If not, then canvas tiles have worked very well for us.

Tardis TimeLine uses a pure brute DOM approach to create timelines. Seeing this and how Vis.js does something similar, drives me to re-implement it removing and adding the time flags. I can't afford to use canvas and it must work on IE 8.

Bit off-topic, but do any of the readers of this topic know of a good combination of an open source (backend) tile server and a (frontend) JS zooming library for dealing with large high-resolution images, of say, something like old paintings?

Like this?

http://www.thekremercollection.com/art/artists/Pieter-Codde/...

It's actually based on Google Maps API, which isn't open source, but OpenLayers has equivalent functionality though I find it less fluid and slower...

Oh, and regarding server side software, a web server is enough if you named the tiles in a logic way. You'll have to provide a callback to OpenLayers to return the name of the tile, similar to this pseudo-code:

GetTileFileName(zoom, x, y) {

    return "/MonaLisa/tiles/z" + zoom + "lon" + x + "lat" + y + ".png";

}

Really simple example at http://lovingmaps.herokuapp.com/gent/

Tiles are on (ahem) dropbox at moment - but S3 / local server would be same. Tiles were generated with TileMill.

there is also http://hugepic.io/ as well as the related github repo at https://github.com/peterbe/tiler

Cool, thanks for all the recommendations people!

Are canvas tiles more performant than one giant canvas sized to fit within a user's browser?

So basically what we wanted to avoid was doing lots of redrawing during panning. If there were a single static canvas with the image tiles moving underneath it, then it would have to constantly redraw during panning. By using tiles, you only have to draw or redraw as necessary, e.g. as you pan to a part of the map outside of the current bounds.

This is great. I use Seatgeek 100% because of their excellent design work.

Maybe someone know wayfinding on HTML5?

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