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AIM-Style Scrolling Banner Control

, 30 Jun 2001
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A scrolling banner control containing strings with individual styles and colors.
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Sample Image - BannerTester.jpg

Introduction

Have you ever wanted to include a control in one of your applications that behaves like a web banner ad with scrolling text that whips by. This effect is also seen with the news ticker on AOL Instant Messenger. A bunch of hyperlinks whip by with news headlines, and you click on the headlines to go to the article. Of course, it wouldn't be very useful if all the strings had to have the same style and color. It would be better if each string was able to have its own individual style and color. This type of thing is possible with the CBannerStatic class. So what do we need to use this control?

Explanation

First off, we're going to need a collection of strings with each string having its own color and style (underlined, italicized, etc) - enter the CString derived CColorString class. It uses a DWORD to hold both the color and value parameters. Since a COLORREF uses only the low 3 bytes to keep track of colors, I use the high byte to store style information such as whether the string is italicized, underlined or bold. CColorString can also store a background color; I waste another DWORD for this. In the future, I may move the style values to BOOL types so that the code is more understandable; we're supposed to get away from bit-masking operations in C++!

Now that we have a class to encapsulate strings that know their own style, we need a control that knows how to display them. Enter CMultiColorStatic. It's quite similar to CColorStatic type controls but it is a static object that will allow multiple strings to be entered with each string having its own style. This is done by having a CPtrArray to keep track of all of the CColorStrings that have been added to the control. Granted, there isn't a whole lot of gain by using one CMultiColorStatic instead of a bunch of CColorStatics; I just wanted one control to be the base for CBannerStatic.

Speaking of CBannerStatic, that's the last piece of the puzzle. CBannerStatic combines scrolling with the flexability of multiple strings. For scrolling, it uses multimedia timers so that similar precision can be achieved on any windows platform (with normal timers, Windows NT has 10ms precision, while Win9x has only 55ms precision). I use the multimedia timers only for precision; when I receive the timer message, I post a WM_TIMER message to the control and the drawing is done in the WM_TIMER handler. When drawing becomes complicated, the app containing the banner could become unresponsive because the drawing takes longer than the scrolling. By this time the drawing is complete and it's time to scroll again. By retaining a message structure, the app will never become unresponsive.

The entire thing is fairly simple to use, but it may take some time getting used to. CBannerStatic provides a neat way to allow the user to click on an item and get results. The client can set an item cursor as well with an ItemClick callback function. It'd be too much to explain everything here, but the sample app BannerTester is pretty comprehensive in demonstrating the feature-set of CBannerStatic (as well as CMultiColorStatic).

Some caveats: The control can be slow if it is made to be large and/or has a lot of message strings. It will bog down the entire system - so beware!

One last note: I don't like to use Precompiled Headers and you'll find that if you just use the classes as provided, the compiler will complain about "StdAfx.h" not being included. If you get this problem, you can just add #include "StdAfx.h" to each cpp file for each of the three classes.

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

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About the Author

PaulWendt
Software Developer (Senior)
United States United States
No Biography provided

Comments and Discussions

 
GeneralEverything is great except... PinmemberAnonymous19-Jun-02 6:25 

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