On 12/15/2010 02:25 AM, Dmitry Torokhov wrote: > On Wed, Dec 15, 2010 at 02:37:54AM +0100, Henrik Rydberg wrote: >> Hi Chase, >> >>> >> >>> I gave this some more thought, and I was close to accepting it with >>> documentation of the above restrictions. Then I thought of how the >>> following two devices would be presented to userspace: >>> >>> 1. A real MT device supporting up to 2 touches (e.g. a bamboo touch) >>> - ABS_{X,Y}, BTN_TOUCH, BTN_TOOL_FINGER, and BTN_TOOL_DOUBLETAP for ST >>> - ABS_MT_SLOT, ABS_MT_TRACKING_ID, ABS_MT_POSITION_{X,Y}, ABS_MT_TOOL_TYPE >>> >>> 2. A partial MT device using MT_TOOL_ENVELOPE (e.g. synaptics MT) >>> - ABS_{X,Y}, BTN_TOUCH, BTN_TOOL_FINGER, and BTN_TOOL_DOUBLETAP for ST >>> - ABS_MT_SLOT, ABS_MT_TRACKING_ID, ABS_MT_POSITION_{X,Y}, ABS_MT_TOOL_TYPE >>> >>> Note that they are identical! The range of values for each axis would be >>> identical too. The only way to tell the two apart would be to watch for >>> the ABS_MT_TOOL_TYPE axis. > > Question: does the driver really need to know this data beforehand? I'd > expect MT-aware driver simply having handlers for both styles and then > doing the best it can with the data stream it gets... There should not > be ambiguity as to what event is - I believe we should be sending > BTN_TOOL_ENVELOPE even for the single/first contact for devices that do > not do full MT tracking. In XI 2.1 with MT, I would envision a partial MT device having different axis labels. We don't want to push an implementation specific abstraction, as MT_TOOL_ENVELOPE is, through the X protocol and require clients to watch the tool type. It should be readily apparent by the axis labels of the position valuators whether they represent true MT coordinates or a bounding rectangle of touches. As for whether clients will want to know if the device is real or partial MT, I think we should design a protocol that allows for a client to know. Maybe the application gives visual feedback on how to perform gestures depending on the device type? Thanks, -- Chase -- To unsubscribe from this list: send the line "unsubscribe linux-input" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html