On Mon, Feb 17, 2014 at 01:42:52PM -0500, Benjamin Tissoires wrote: > X and Y are li_fixed_t, which is 24.8 fixed point real number. > li_fixed_t max is thus ~8388607. > > On a touchscreen with a range of 32767 values (like a 3M sensor), and > mapped on monitor with a resolution of 1920x1080, we currently have: > (x - li_fixed_from_int(device->abs.min_x)) * width == 62912640 > > which is 7 times bigger than li_fixed_t max. > > To keep the precision of the sensor, first compute the uniformized > coordinate (in range 0 .. 1.0) of the touch point, then multiply it > by the screen dimension, and revert it to a li_fixed_t. > > Signed-off-by: Benjamin Tissoires <benjamin.tissoi...@gmail.com> > --- > > Hi, > > I have hit this problem by playing with a touchscreen reporting 4096 values, > on > xf86-input-libinput. xf86-input-libinput does not use the real screen size, > but > 0xffff instead. This allows to report a touchscreen with a range of 128 values > to work properly :( > > I went through the multitouch device database, and took one example of a more > real use-case (xf86-input-libinput is still in an early shape).
fwiw, this is exactly the type of use-case where it would be simple and worth it to knock up a test for a single device and make sure that the coordinates are correct. which gives us a nice reproducer and prevents us from errors like this in the future. > src/evdev.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/src/evdev.c b/src/evdev.c > index d8dff65..0d033b8 100644 > --- a/src/evdev.c > +++ b/src/evdev.c > @@ -91,8 +91,9 @@ evdev_device_transform_x(struct evdev_device *device, > li_fixed_t x, > uint32_t width) > { > - return (x - li_fixed_from_int(device->abs.min_x)) * width / > + double x_scaled = (li_fixed_to_double(x) - device->abs.min_x) / > (device->abs.max_x - device->abs.min_x + 1); > + return li_fixed_from_double(x_scaled * width); A simple 1L * .... should suffice, right? Cheers, Peter > } > > li_fixed_t > @@ -100,8 +101,9 @@ evdev_device_transform_y(struct evdev_device *device, > li_fixed_t y, > uint32_t height) > { > - return (y - li_fixed_from_int(device->abs.min_y)) * height / > + double y_scaled = (li_fixed_to_double(y) - device->abs.min_y) / > (device->abs.max_y - device->abs.min_y + 1); > + return li_fixed_from_double(y_scaled * height); > } > > static void > -- > 1.8.5.3 > _______________________________________________ wayland-devel mailing list wayland-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/wayland-devel