Mir considered about Multi-display && Multi-touch devices?

[Daniel van Vugt]

Leslie,

XMir does not use Mir's input system at the moment. It lets X use the 
existing evdev interface instead. Also, XMir does not use Mir's hardware 
cursor either. So it is X rendering the mouse pointer(s) in software.

So in theory your issue has nothing to do with Mir and would still 
happen in plain X too. I think you should direct the problem to an X 
mailing list.

- Daniel


On 19/10/13 12:54, Leslie Zhai wrote:
> Hi Mir developers,
>
> I use Projected Capacitive touch screen device
> http://en.wikipedia.org/wiki/Touchscreen#Projected_capacitance
> It can be pasted on the normal monitor, then it is able to touch, the
> cursor will move to the position where touched. It experienced like
> iphone and other single touch screen device.
>
> But when I put multiple Projected Capacitive touch screen devices on
> several monitors, then touch some of them simultaneously, the cursor of
> X Window was only moving in the first monitor, even though it was able
> to move to other monitors` display, it still failed to show the correct
> position. Did Mir consider about Multi-display && Multi-touch devices?
>
> Why the cursor of X Window wired? Some people might argue that it is
> Linux kernel Multi-touch Protocol issue
> https://www.kernel.org/doc/Documentation/input/multi-touch-protocol.txt
>
> Nope!
>
> For Protocol Example B
>
> Here is what a minimal event sequence for a two-contact touch would look
> like for a type B device:
>
> ABS_MT_SLOT 0
> ABS_MT_TRACKING_ID 45
> ABS_MT_POSITION_X x[0]
> ABS_MT_POSITION_Y y[0]
> ABS_MT_SLOT 1
> ABS_MT_TRACKING_ID 46
> ABS_MT_POSITION_X x[1]
> ABS_MT_POSITION_Y y[1]
> SYN_REPORT
>
> Here is the sequence after moving contact 45 in the x direction:
>
> ABS_MT_SLOT 0
> ABS_MT_POSITION_X x[0]
> SYN_REPORT
>
> Here is the sequence after lifting the contact in slot 0:
>
> ABS_MT_TRACKING_ID -1
> SYN_REPORT
>
> The slot being modified is already 0, so the ABS_MT_SLOT is omitted. The
> message removes the association of slot 0 with contact 45, thereby
> destroying contact 45 and freeing slot 0 to be reused for another contact.
>
> Finally, here is the sequence after lifting the second contact:
>
> ABS_MT_SLOT 1
> ABS_MT_TRACKING_ID -1
> SYN_REPORT
>
> Here ABS_MT_SLOT distinguished which finger touch the screen,
> ABS_MT_POSITION_X and ABS_MT_POSITION_Y shown the position where the
> finger touched.
> In case ABS_MT_XXX martix like below:
>
> (0, 0)-------------------------(4075, 0)
> | |
> | |
> | |
> | (X, Y) |
> | |
> | |
> | |
> | |
> | |
> | |
> | |
> (0, 4095)-------------------(4075, 4095)
>
> For single touch screen device situation, the X axis range of the
> position is [0, 4075], the Y`s is [0, 4095]; then for multi-devices, the
> matrix could not be transformed, the range might never be changed, it
> will not increased by multiply the number of monitors. It means if I
> could touch several monitors in the same or about position
> simultaneously, I am so lucky :) the (X, Y) position values might be the
> same, then the cursor of X Window wired.
>
> Then someone might be doubt about it is X evdev input driver issue
> http://cgit.freedesktop.org/xorg/driver/xf86-input-evdev/
>
> In the function EvdevAddAbsValuatorClass(DeviceIntPtr device, int
> want_scroll_axes)
> http://cgit.freedesktop.org/xorg/driver/xf86-input-evdev/tree/src/evdev.c#n1249
>
> It only consider about one single device, a Projected Capacitive touch
> screen device connected to Linux box via USB, but what about multi-touch
> devices, how to handle several file descriptors? It might be fixed by
> Leslie MultiTouch way!
>
> Leslie MultiTouch
>
> I hacked the get devices function via reading /proc/bus/input/devices
>
> void getDevices(std::string DeviceName, std::vector<std::string>* Devices)
> {
> std::string strLine;
> std::string strDevPath;
> std::ifstream DevFile("/proc/bus/input/devices");
> int nPos;
>
> while (std::getline(DevFile, strLine))
> {
> if (strLine.size() == 0)
> continue;
>
> if (strLine[0] == 'N')
> {
> if (ToLower(strLine).find(ToLower(DeviceName)) != std::string::npos)
> {
> while (std::getline(DevFile, strLine))
> {
> if (strLine[0] == 'H')
> break;
> }
> nPos = strLine.find("event");
> if (nPos != std::string::npos) {
> strDevPath = "/dev/input/" + strLine.substr(nPos, strLine.size() - nPos
> - 1);
> #if DEBUG
> // such as /dev/input/event13
> std::cout << "DEBUG: " << strDevPath << std::endl;
> #endif
> Devices->push_back(strDevPath);
> }
> }
> }
> }
> }
>
> Then it need to create a thread pool to handle several DeviceIntPtr
> objects simultaneously.
>
> And it need to identify each touch screen device like Xorg Xinerama conf
> style:
>
> Section "MultiTouchLayout"
> Identifier "MultiTouch Device"
> Device 0 "Device0" 0 0
> Device 1 "Device1" RightOf "Device0" # LeftOf, BelowOf, AboveOf
> Option "MultiTouch" "true"
> EndSection
>
> Section "Device"
> Identifier "Device0"
> Device "/dev/input/event13"
> Monitor "Monitor0"
> DefaultDepth 24
> SubSection "Display"
> Viewport 0 0
> Depth 24
> Modes "1680x1050"
> EndSubSection
> EndSection
>
> Section "Device"
> Identifier "Device1"
> Device "/dev/input/event16"
> Monitor "Monitor1"
> DefaultDepth 24
> SubSection "Display"
> Viewport 0 0
> Depth 24
> Modes "1680x1050"
> EndSubSection
> EndSection
>
> When it send a (X, Y) position event from the touch screen devices`
> thread pool, it is able to know which device generate it, and it need to
> transform the old (X, Y) position to monitor_N`s new (X`, Y`), the
> cursor of X Window might never wired any more.
>
> Best Regards,
>
> Leslie
>