On Mon, Dec 13, 2010 at 10:36 PM, Peter Hutterer <peter.hutterer@xxxxxxxxx> wrote: > On Tue, Dec 14, 2010 at 12:25:26AM +0100, Henrik Rydberg wrote: >> >> The envelope contacts serve as a way to detect a small area of fingers or a >> >> >> large area of fingers. There is nothing inherently problematic with having one >> >> or three or more such contacts. >> > >> > Then I'm more confused :). >> > >> > I see one problem: devices that report two touch points, (X1, Y1) and >> > (X2, Y2), but in reality the touches could be at (X1, Y2) and (X2, Y1) >> > instead. Using a rectangle helps resolve this issue for panning and >> > pinching, though not for rotation. >> >> >> If panning and pinching and rotation could all be recovered properly, then the >> individual contacts could actually have been reconstructed properly in the first >> place. This is the whole point - there is not enough information available for >> rotation to be recovered properly. > > can you post an example event stream of the MT_ENVELOPE tool? I'm having > trouble wrapping my head around it. > Patch 2/2 of synaptics patches from Henrik show this in code form but here is text form. Its sets up 2 MT slots and start out at (x,y)=(0,0) for both slots with no fingers touching. When 1 finger touches, slot 0 shows (x,y) as reported by hardware and keeps slot 1 at (0,0). When 2 fingers touch, slot 0 shows lower left of rectangle and slot 1 shows upper right corner. When 3 fingers touch, same thing as 2 fingers. For 1 finger case, we could send duplicate values of slot 0 into slot 1 but (0,0) is more efficient for more typical 1 finger usage. The 3 finger case helps show that hardware itself really wants to talk in terms of rectangles as well, even if they give half hearted attempts at real multi-touch points. Since these slots need to be treated as a whole, no tracking id or similar. 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
