experimental multitouch based smooth scrolling

high-resolution mouse wheels aren't supported in userland yet, so why
don't we fake a high resolution touchpad instead 😄

it's somewhat working, though it seems to crash on startup when
installed (among other weird bugs).

src/controller/controls/mod.rs

@@ -2,6 +2,7 @@ mod media;
 mod null;
 mod paddle;
 mod scroll;
+mod scroll_mt;
 mod volume;
 mod zoom;
 
@@ -9,5 +10,6 @@ pub use self::media::*;
 pub use self::null::*;
 pub use self::paddle::*;
 pub use self::scroll::*;
+pub use self::scroll_mt::*;
 pub use self::volume::*;
 pub use self::zoom::*;

src/controller/controls/scroll_mt.rs

@@ -0,0 +1,61 @@
+use crate::controller::{ControlMode, ControlModeMeta};
+use crate::dial_device::DialHaptics;
+use crate::fake_input::FakeInput;
+use crate::DynResult;
+
+pub struct ScrollMT {
+    acc_delta: i32,
+
+    fake_input: FakeInput,
+}
+
+impl ScrollMT {
+    pub fn new() -> ScrollMT {
+        ScrollMT {
+            acc_delta: 0,
+            fake_input: FakeInput::new(),
+        }
+    }
+}
+
+impl ControlMode for ScrollMT {
+    fn meta(&self) -> ControlModeMeta {
+        ControlModeMeta {
+            name: "Scroll",
+            icon: "input-mouse",
+        }
+    }
+
+    fn on_start(&mut self, haptics: &DialHaptics) -> DynResult<()> {
+        haptics.set_mode(false, Some(3600))?;
+        self.acc_delta = 0;
+
+        self.fake_input.scroll_mt_start()?;
+
+        Ok(())
+    }
+
+    fn on_end(&mut self, _haptics: &DialHaptics) -> DynResult<()> {
+        self.fake_input.scroll_mt_end()?;
+        Ok(())
+    }
+
+    // HACK: the button will reset the scroll event, which sometimes helps
+
+    fn on_btn_press(&mut self, _: &DialHaptics) -> DynResult<()> {
+        self.fake_input.scroll_mt_end()?;
+        Ok(())
+    }
+
+    fn on_btn_release(&mut self, _haptics: &DialHaptics) -> DynResult<()> {
+        self.fake_input.scroll_mt_start()?;
+        Ok(())
+    }
+
+    fn on_dial(&mut self, _: &DialHaptics, delta: i32) -> DynResult<()> {
+        self.acc_delta += delta;
+        self.fake_input.scroll_mt_step(self.acc_delta)?;
+
+        Ok(())
+    }
+}