On 07/30/2010 08:55 PM, Éric Piel wrote: > On 21-07-10 05:36, Dmitry Torokhov wrote: >> On Mon, Jun 21, 2010 at 11:06:28PM +0200, Éric Piel wrote: >>> When 2 fingers are pressed, the low and high coordinates are given. >>> Instead of reporting just the low coordinate as the normal position, >>> report an average of both. This allow to have the cursor always move, >>> whichever finger moves. In practice, this improves the support of >>> two-fingers scolling with the synaptics X driver. > : >>> - input_report_abs(dev, ABS_X, x1<< 2); >>> - input_report_abs(dev, ABS_Y, y1<< 2); >>> + input_report_abs(dev, ABS_X, (x1 + x2)<< 1); >>> + input_report_abs(dev, ABS_Y, (y1 + y2)<< 1); >> >> I am concerned what happens when you put one finger first and then add >> another one. Would not that couse the cursor to jump? I agree, I have seen this behavior before and it is not quite what you want. The average point does jump. >> I'd say we need to obey MT protocol and continue reporting the first >> contact in non-MT protocol and rely on MT-aware drivers to do better job >> of contact tracking. This is also consistent with how other drivers, >> such as bcm5974, report coordinates. > If the MT protocol says we should always report on the single-touch side > the first contact, then I guess it's better to do so. However, I've just > read the latest version of the mt-protocol document, and couldn't see > anything saying that. Are you sure this is the official behavior? I'd > tend to think that single-touch and multi-touch are never read together, > so they can be different. It is true that there are no specific section on how to handle the ABS_X/Y events, and different drivers have slightly different strategies. However, common to them all is that a single finger is consistently used to report the events. > More specifically, on this hardware, when there are two fingers, we get > only the lower coordinates and the higher coordinates, but we don't know > exactly where are the fingers. As there is no tracking, the lower > coordinate might be the second finger applied, so even if we report just > the lower coordinates, there is 75% chance that the cursor will jump. Perhaps it is better to not report ABS_X/Y at all in the case of two fingers on this trackpad. With any reasonable userspace driver, the ABS_X/Y will be masked out anyways. > That's actually the reason I prefer the average: it gives a 100% > expectable behavior (because the average is always correct). In > practice, when using the xorg synaptics driver, with the default > 2-fingers-scrolling mode, the cursor never jumps because as soon as the > second finger is applied, X and Y are not used to move the cursor. It is predictable, but it is still bad behavior. ;-) > So, I think this patch is an improvement for the user, but if you think > that it would not respect the MT protocol, just drop it. Either dropping the patch or muting ABS_X/Y in case of multiple fingers is what I would recommend. Cheers, Henrik -- 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
