Rick's b.log - entry 2017/02/26

My blog been kind of quiet recently? That's because I was cooking a few things. Here's the other thing I've been cooking...

Tablet driver

Now, this product is on CJE's website at http://www.cjemicros.co.uk/micros/individual/newprodpages/prodinfo.php?prodcode=WAC-GT1 at a cost of £114 (for UK customers).

There have been some mutterings about the cost over the price of the tablet alone. So please let me take a moment to inform you of a few things. The first thing to understand is that while tablets based upon the same chip will use the same protocol (kind of like how all the Pi family can run RISC OS), there are almost as many tablet controller chips as there are tablets (kind of like how the majority of cheap'n'cheerful ARM boards can't run RISC OS 'cos they're all different). As such, there was no hope of a one-size-fits-all tablet driver.
Because of this, CJE actually sent me several potential tablets to try. Unfortunately by the time the tablet has been connected to RISC OS, it will have downgraded its abilities to be a mouse emulation. To have otherwise would mean a tablet driver actually built into RISC OS to get at the device before the USB stack starts messing with it. In this situation, a number of tablets provide co-ordinates but no pen pressure (the bytes are sent, but either as fixed bogus values or as zero). A stylus without any pressure report is...useless.
To add to the fun, most of the HID blocks provided by the tablets are rubbish. Indeed, the Wacom tablet describes itself as "n bytes of undefined purpose". Looking on the Wacom developer website says, and I quote: There is generally no good reason to directly communicate with the tablet instead of using Wintab, but if you have a unique situation, you can contact Wacom's Product Management (...email...) to see about signing an NDA.
An NDA? Sheesh. Obviously getting nowhere with that avenue, the actual tablet was sent to me so I could plug it in and perform the time-honoured tradition of "doing stuff" and seeing how it altered the data flow. Only to discover that the protocol was indeed complex. And a tad hairy in places. Lots of fun to deal with.
Then we hit the problem of screen aspect ratio. That is to say that if one draws a perfect circle on the tablet, what will appear on the screen will probably be an oval. It's because the tablet's active area is a fixed size, and is probably not the same sort of dimensions as your screen. So what was necessary was to provide a way to work out what was necessary, and then introduce borders in the active area (that is to say, if you are using a 16:9 monitor, your tablet will have null areas at the top and bottom of the active area) so that what is drawn on the tablet will exactly correspond with what appears on-screen.
But the better part is that I developed this on my Pi, so each test version was sent back to CJE for verification that it worked as expected on other hardware; such as an iMX.6 or Ti with different display than mine.

I'm missing out a load of detail that isn't really pertinent, suffice to say that CJE's markup on the product isn't simply a matter of taking my driver and Wacom's tablet and sellotaping one to the other. There was a lot of stuff that went on beforehand that got us to the place where CJE could offer a product for sale. Because it is important to CJE (and to me) that the product offered be one that works. A known combination of elements to give you results. Because, if you handn't figured it out from above, loading up the driver and using it with a tablet you got off of eBay is most likely to result in failure. Plus the expense of a useless tablet. An expense that CJE endured, several times, in their search for a good combination for you. You, as the customer, don't get these headaches. You don't get to scour eBay looking for some part that might work. You get http://www.cjemicros.co.uk/micros/individual/newprodpages/prodinfo.php?prodcode=WAC-GT1 that has already been tested, and was demonstrated at the recent show.

Okay, I'll get off my soapbox now. ☺

I redrew the girl from that manga (well, retraced it might be more accurate as my drawing ability is that of a blind toddler), and here it is as drawn in about ten minutes on the Wacom with PhotoDesk:

Pi unboxing

The automatic subtitle transcription gave such joy as "the stuff people could actually flip out" and "something this machine when I get a new DJ and donuts with the probably my machine". So I decided the only sensible thing to do was to create my own subtitles in English and French.

The video is also available in FullHD, nd was created entirely on my Samsung Galaxy S7.

And, as the video ends, so shall this blog article: Thanks David!

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Zerosquare, 2nd March 2017, 10:19

It's nice to see that there still are companies willing to support alternative/obsolete stuff :)

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