On Fri, Jul 30, 2010 at 4:41 PM, Éric Piel <E.A.B.Piel@xxxxxxxxxx> wrote: > > Op 30-07-10 23:01, Henrik Rydberg schreef: > > On 07/30/2010 08:55 PM, Éric Piel wrote: > : > >>> 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. > > This is basically same approach as what synaptics hardware is reporting. Their Synaptics PS/2 TouchPad Interfacing Guide mentions current hardware reports an x/y closer to first finger during multiple fingers and that older hardware reports a value closer to center. Both cases, you can see movement when either finger is moving. There are a few existing X side bug reports I've seen related to this behaviour. On newer synaptics pad its easiest to see if you touch 1st finger on left side of pad, 2nd finger on right side of pad, and then release 1st finger then you will see a big cursor jump as hardware is force to transition over to 2nd finger x/y (make sure 2 finger scrolling is disabled as that feature can fix issue). I've seen xf86-input-synaptics patches floating around that try to detect jumps-because-of-averaging from the size of delta and discard but it is easy to be mistaken. Probably its better to detect BTN_TOOL_DOUBLETAP transitions back to 0 and treating similar to both fingers being lifted to account for expected jump. So an option is to do something similar to below and clearly document that user space needs to account for known reporting behaviour when BTN_TOOL_DOUBLETOUCH transitions back to 0. input_report_abs(dev, ABS_X, x1 + (x2 & 7)); input_report_abs(dev, ABS_Y, y1 + (y2 & 7)); Chris -- 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
