Digital Signage: Implementing a smooth scrolling text

Many digital signage hardware feature scroll text. However, in many cases the scrolling text is either not smooth, sometimes teared or very slow.

It may depends on the performance of the hardware used but also on the implementation of the software.

Once easy way to implemented scrolling text is just to redraw the text again and again at different position. However, this is very slow and yields poor results unless maybe you have a Truetype accelerator or similar hardware font accelerator.

The next step is then to convert the text into pixmaps. This can either be done in the digital signage manager software (Windows PC/MAC or Linux based) or the digital signage player. Doing so in the latter makes it much more flexible.

So you may create 2 pixmaps whose width and length match the region to be displayed, you write the text on those 2 pixmaps, then simply move those 2 pixmaps, and once one is fully displayed, you refresh it off screen before displaying again.

2 pixmaps for smooth scrolling text

In the example above, assuming a left to right scrolling text “THIS IS A SM” is written to pixmap 1, “MOOTH SCRO” to pixmap2 and once pixmap 1 is fully displayed, refresh it and write “OLLING TEXT” inside it and etc..

Once this is properly implemented, this may yield decent results depending on the resolution used. If this is still not smooth, make use of the 2D graphic accelerator (if any)  that have move rectangle operation.

This has been tried on Digital Signage hardware using Sigma Designs EM8623 and SMP8635 platforms. Although those two platforms do have Truetype font graphic accelerator they could not be used in our designs due to font memory limitations in the hardware accelerator, as we had to use East Asian fonts.

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