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 <[email protected]> --- 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). Cheers, Benjamin 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); } 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 [email protected] http://lists.freedesktop.org/mailman/listinfo/wayland-devel
