Friday, November 29, 2013

Interactive Embedded Touch GUIs with HTML5

Recently we've been considering graphical user interfaces (GUIs) from the point of view of a systems integrator. There are several thing to consider, when creating a complete solution, such as: several different software platforms ( embedded devices, phones, tablets, desktop computers, ...), data network considerations and future proofing.

Several technical solutions come to the rescue here. Firstly, there are standards that span several (all involved) platforms and allow software development to be done once - with perhaps some adaptation for each platform. Secondly, networks of all sizes and shapes allow for powerful distributed systems, where data can be shared and interaction happens across the room or from the other side of the globe.

The Ixonos Embedded HTML5 library - ixgui.js - has proven to be a highly flexible and scalable platform for creating embedded GUIs. Recently, a number of system topologies have been explored using ixgui.js, involving running the GUI as detached from the embedded device. HTML5 obviously fits natively into this kind of distributed environment. The GUI can be hosted on the cloud, on an embedded device or basically anywhere.

Sensor data sharing in our demonstrator is fascilitated using the Ixonos sensact library, which you can read about in an earlier blog post.

The user interface for this demo is simple. It displays data coming in from the TI Sensor Hub Booster Pack. In addition, there is an RPM display and setting slider, but that is only for show: there is no motor in this version - but in later ones there will. below is a screenshot of the GUI:

Simple Touch Interface using ixgui.js
The below video illustrates using this GUI on the Texas Instruments AM3359 Evaluation Module with a separate, more elaborate, GUI running on a detached display.

ixgui.js is a HTML5-based GUI library, which allows performance optimized GUI creation by using the Canvas 2D interface for fast graphics and fine control over what is drawn at a given time. It is designed around the principles of simplicity, performance, standards compliance and programmer friendliness.

This article outlines some key methods for improving Canvas 2D performance. It has been extremely gratifying to fine-tune drawing for ixgui.js, and indeed we implement optimization on several levels.

On the top level, rendering is optimized by only drawing what needs to be redrawn. For most GUIs, only when items are interacted with, do they require to be redrawn.

Pre-rendering: often a large part of an item is static, and actually requires no update at all during the entire lifecycle of an application. In these cases, we can simply pre-render those areas that don't change onto a separate buffer, and reuse that for each redraw. As an example, see the below picture for how the vertical sliders in the demo are drawn:

Finally, at the lowest level possible (in JavaScript), some optimization is achieved by only feeding integer values to drawing routines. All coordinates and dimensions throughout the GUI are cast to integers.

Mikael Laine, SW Specialist - Ixonos

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