On Tue, Feb 15, 2005 at 06:40:37PM -0500, Dan Streetman wrote: > > Hi Vojtech, > > I have a question about the "contract" of the evdev interface... > > I have 2 touch screens, both USB. Both of them have drivers (hid-input > and mtouchusb) that provide ABS_X and ABS_Y coordinates to the input > subsystem and so I read those coordinates from userspace. > > However, one of the touch screens (ELO, via hid-input) reports coordinates > with the origin in the upper-left corner, i.e. touching the upper-left > corner of the screen reports 0,0. The other touch screen (3M, via > mtouchusb) reports coordinates with the origin at the bottom-left corner. > > So my question is, can an evdev app assume a specific origin?
Yes, Linux input layer defines decreasing values to be the same as HID, that is up, far from the user, and left. Zero can be anywhere, but if only positive values are returned, it must be in the upper left corner. > Normal screen origin, i.e. upper-left, would make the most sense to > me. If so, it seems that mtouchusb should flip its Y coordinates > before sending to the input subsystem (which would be an easy patch of > course). It doesn't flip them while it should flip the Y coordinate. This is because many touchscreens have [0,0] in their bottom left corner by hardware, being in the 1st quadrant, which is considered most logical by many. I fixed it in my tree. > Or, can an app not rely on evdev's coordinate origin being > upper-left? Yes and no. You can rely that the driver will try to have [0,0] in the upper left corner, however this can be marred by the user turning the touchscreen 180 degrees on the monitor to get the cables on a more convenient side. This happens quite often. A complete matrix axis transformation is necessary then. -- Vojtech Pavlik SuSE Labs, SuSE CR ------------------------------------------------------- SF email is sponsored by - The IT Product Guide Read honest & candid reviews on hundreds of IT Products from real users. Discover which products truly live up to the hype. Start reading now. http://ads.osdn.com/?ad_id=6595&alloc_id=14396&op=click _______________________________________________ linux-usb-devel@lists.sourceforge.net To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
