On 09/06/2011 11:47 AM, Henrik Rydberg wrote: >>>> I see that the current code scales the coordinates for v2, but it's only >>>> half-resolution. That's not a huge deal since the resolution of modern >>>> touchpads is very high. We could leave it scaled to not break abi, if >>>> that was a concern. However, with new devices it makes sense to state >>>> the ranges in terms of what the device actually supports. Otherwise, >>>> we're just masking out useful data that userspace could be using. >>>> >>> >>> I disagree. I believe that ST and MT ranges reported for the same >>> working surface should match, especially since many devices derive ST >>> data from MT. >>> >>> As far as devices that have ranges 0-15 in MT mode - I am not sure how >>> useful such MT steam anyway and if we are better of just ignore them >>> (maybe just use the data to report number of fingers on the surface but >>> otherwise use standard ST protocol). >> >> The MT data could still be useful for pinch to zoom or potentially >> rotate (though most low res devices probably are only semi-mt). I don't >> want to forsake pinch to zoom just because we can't pass on the >> resolution of MT data properly. > > We are not forsaking anything. At best, the detail missed out by using > the same scaling for ST and MT is the ability to distinguish the axis > with the best or poorest resolution. However, some devices report > higher MT than ST resolution, not because it is better (it is indeed > worse), but simply to not lose bits in the filtering process. In other > words: the logic is not without corner cases, and it only makes a > difference to the transitional devices that are not fully MT > capable. If this really was a concern, userspace could use the ST > coordinates for some transformations instead. So what do we want userspace to do? In the absence of supplying this information we need to provide guidelines. We could say: * Always use ST coords + finger count for drag gestures (i.e. scrolling) * Use MT coords for pinch and rotate If this is acceptable, we should add it to the documentation. Thoughts? -- 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
