<html> <head> <base href="https://bugs.freedesktop.org/"> </head> <body> <div> <a class="bz_bug_link bz_status_NEEDINFO " title="NEEDINFO - Acceleration still too fast with slow and slow-medium finger movements" href="https://bugs.freedesktop.org/show_bug.cgi?id=101139#c44">Comment # 44</a> on <a class="bz_bug_link bz_status_NEEDINFO " title="NEEDINFO - Acceleration still too fast with slow and slow-medium finger movements" href="https://bugs.freedesktop.org/show_bug.cgi?id=101139">bug 101139</a> from <a class="email" href="mailto:peter.hutterer@who-t.net" title="Peter Hutterer <peter.hutterer@who-t.net>"> Peter Hutterer</a> <pre>Created <a href="attachment.cgi?id=138716" name="attach_138716" title="synaptics-libinput-comparison.svg">attachment 138716</a> <a href="attachment.cgi?id=138716&action=edit" title="synaptics-libinput-comparison.svg">[details]</a> synaptics-libinput-comparison.svg Please keep this bug on-topic, the hysteresis issues are not for this bug. Attaching my best efforts to compare synaptics and libinput for archival purposes. The libinput curve is printed directly with the ptraccel-debug tool (this is git master without the patches above). For the synaptics curve, I created a uinput device that moves a touch from left to right at decreasing time intervals and eventually gets to the maximum speeds shown. The various values were printed as YAML to the xorg.log and extracted from there with custom python scripts. Since the server uses device coordinates everywhere, I divided the velocity for synaptics values by the resolution I used in the uinput device. This should give us mm. The curves shown in the diagram are: "synaptics" - the accelfct as returned from SynapticsAccelerationProfile for a given speed. Notice how the curve isn't too dissimilar to the libinput curve in shape, albeit the libinput curve includes the final accel factor. "mult" - the multiplier used in the server's acceleratePointerPredictable(), after taking constant deceleration and the synaptics acceleration factor into account. This mult factor is then applied to the input deltas (these are in device coordinates) and the closest match to the 'accel factor' that libinput uses (but see below). "libinput" - libinput accel factor applied to a delta at any given speed. Constant deceleration in synaptics is 1/2.5 (0.4), and quite similar to the MAGIC we use in libinput (0.37). That latter one was found by trial and error but having those two similar indicates this is a good value. I haven't even tried to change synaptics acceleration options, this makes it even harder... To the best of my knowledge, the curves are correct. But honestly, this is all so convoluted that it's hard to be sure. And note that after applying the acceleration factor, the device coordinates are scaled into screen coordinates which depends on the screen resolution. IOW, different results for larger screens (or screens with different aspect ratios). And for all I know, this may change the curve significantly but this is even harder to test because the rescaling will clip at screen edges and my testing approach hit those very quickly. Also, neither libinput nor synaptics are that simple, there is some analysis of previous events to adjust the acceleration curve (e.g. on directional changes).</pre> </div> <hr> You are receiving this mail because: <ul> <li>You are the assignee for the bug.</li> </ul> </body> </html>