Race across screens and platforms, powered by the mobile web

JUN 11, 2013
Author Picture By Pete LePage, Chromium team

Cross-posted with the Chromium Blog

You may have seen our recent demo of Racer at Google I/O, and wondered how it was made. So today we wanted to share some of the web technologies that made this Chrome Experiment “street-legal” in a couple of months. Racer was built to show what’s possible on today’s mobile devices using an entirely in-browser experience. The goal was to create a touch-enabled experience that plays out across multiple screens (and speakers). Because it was built for the web, it doesn’t matter if you have a phone or a tablet running Android or iOS, everyone can jump right in and play.
Racer required two things: speedy pings and a consistent experience across screens. We delivered our minimal 2D vector drawings to each device’s HTML5 Canvas using the Paper.js vector library. Paper.js can handle the path math for our custom race track shapes without getting lapped. To eke out all the frame rate possible on such a large array of devices we rendered the cars as image sprites on a DOM layer above the Canvas, while positioning and rotating them using CSS3’s transform: matrix().

Racer’s sound experience is shared across multiple devices using the Web Audio API (available in latest iOS and Android M28 beta). Each device plays one slice of Giorgio Moroder’s symphony of sound—requiring five devices at once to hear his full composition. A constant ping from the server helps synchronize all device speakers allowing them to bump to one solid beat. Not only is the soundtrack divided across devices, it also reacts to each driver’s movements in real time—the accelerating, coasting, careening, and colliding rebalances the presence of every instrument.

To sync your phones or tablets, we use WebSockets, which enables rapid two-way communication between devices via a central server. WebSocket technology is just the start of what multi-device apps of the future might use. We’re looking forward to when WebRTC data channels—the next generation of speedy Web communication—is supported in the stable channel of Chrome for mobile. Then we’ll be able to deliver experiences like Racer with even lower ping times and without bouncing messages via a central server. Racer’s backend was built on the Google Cloud Platform using the same structure and web tools as another recent Chrome Experiment, Roll It.

To get an even more detailed peek under the hood, we just published two new case studies on our HTML5 Rocks site. Our friends at Plan8 wrote one about the sound engineering and Active Theory wrote one about the front-end build. You can also join the team at Active Theory for a Google Developers Live event this Thursday, June 13, 2013 at 3pm GMT for an in depth discussion.

Pete LePage is a Developer Advocate on the Google Chrome team and helps developers create great web applications and mobile web experiences.

Posted by Ashleigh Rentz, Editor Emerita