LightCharts

A lightweight line-chart library for Flex.

Background

I created LightCharts for a project of mine that involves tracking many stock market symbols. Originally I was using the Adobe Flex Charting library, but found that performance suffered greatly given the number of charts I was using (around 60+), the amount of data displayed, and the constant real-time updates. Of course this isn’t necessarily due to poor coding on Adobe’s part, it’s just that their library contains an amazing amount of features to handle a variety of needs, consequently it’s very heavy. I didn’t need a lot of features, just a nimble way to display data.

I searched the Internet for other charting libraries which I could use and stumbled across a fantastic set of components created by Keith Peters called Minimal Comps. Keith’s library is extremely lightweight and it would have been a good fit, but MinimalComps is geared towards the pure Flash environment and not Flex – a major issue being the disparity in the component lifecycle.

Nonetheless, I was inspired by his code so I decided to use it as a starting point, adding and changing what I needed along the way.

Features

The result is a charting library that has many new features and several new object classes, some for visual enhancements and others for displaying and interacting with data. For instance, the data series class gives the ability to display multiple lines on a graph. The Toolset architecture is useful for creating mini plug-ins which can annotate or interact with data, all without needing to change any of the charting base classes.

Also, the line-chart class can be subclassed to create new line-chart types which have different visual characteristics or behavior. Included are a couple of examples for charts which I used in my project – these include the MACD and Stochastic. Note: These examples show how to make visual and behavioral changes to the base class, not how to calculate the values for the MACD or Stochastic charts. Those formulas can be easily found online.

Screenshot

In the screenshot above you can see many of the features:

• Three different charts (standard, MACD, and Stochastic), displaying different backgrounds including gradients and alphas, line colors, value ranges, etc.
• On the first chart, the display of crosshairs and coordinate value on mouseover; all charts have this functionality.
• On the first and second charts, a custom plug-in called DotDisplayTool which displays a dot over the last data point in the series. DotDisplayTool is an example of a non-interactive plug-in.
• On the second and third charts, a custom plug-in called LinearDrawTool which allows you to draw on top of the data; it displays a line and the chart values which correspond to the beginning and ending points. LinearDrawTool is an example of an interactive plug-in.

Live Demo & Source

If you want to see the library in action, click on the following link: LightCharts live demo.

The source is covered under the MIT license and it’s currently available from the live demo “View Source…”.

I built it using the Adobe Flex framework. You can get more information about KryptoPhoto at MentalHijack.com.

One example app which helped me greatly was from a blog posting by Ely Greenfield. If you’re interested, you can view it on his website: chart annotation demo.

Unfortunately, the code you can download from his site is a little old so it has problems compiling in Flex Builder 2+. I have updated the code, fixed some bugs in it and have it available here: download OverlayDemo-fixed.zip.

Ely has other interesting demos on his site which are worth checking out. Some of my favorites are: the variable radius pie chart demo, the interactive bubble chart demo, and the dashed lines demo.

Resources

annotation example by Ely Greenfield

• http://www.quietlyscheming.com/blog/2006/04/03/custom-chart-annotations/
• demo: http://demo.quietlyscheming.com/overlayDemo/index.html

annotation example by Brendan Meutzner

• http://www.stretchmedia.ca/blog/index.cfm/2007/3/28/Chart-Milestones-using-annotationElements
• demo: http://www.stretchmedia.ca/code_examples/chart_milestone/main.html

I found what I was looking for in the article “An architectural blueprint for Flex applications” written by Joe Berkovitz. In it he talks about a way in which he architects Flex applications using pure Flex/Actionscript constructs.

Being a Flex newbie, I learned a lot from his article like how to pass variables to your own MXML tags and even customize them using Actionscript. His architecture also solves an issue I was having with Event messaging/bubbling due to the fact that it only works automatically on DisplayObject components. His design also has an interesting way of handling multiple data-services as well as the operations required for handling service communication.

Source code for the project is available in the article. I would recommended downloading it and browsing through the files.

Resources:

• “An architectural blueprint for Flex applications” written by Joe Berkovitz, http://www.adobe.com/devnet/flex/articles/blueprint.html