1 files changed, 107 insertions, 0 deletions
diff --git a/src/event_filter.rs b/src/event_filter.rs
new file mode 100644
index 0000000..9eb4620
--- /dev/null
+++ b/src/event_filter.rs
@@ -0,0 +1,107 @@
+use crate::cirque::TouchData;
+
+use core::{
+    cmp,
+    ops::Sub,
+};
+
+#[derive(Copy, Clone, Debug)]
+pub struct Point<T>(pub T, pub T);
+
+impl<T> Point<T>
+where
+    T: Sub<Output = T>,
+{
+    pub fn delta(self, p: Point<T>) -> Point<T> {
+        Point(p.0 - self.0, p.1 - self.1)
+    }
+}
+
+impl Point<isize> {
+    pub fn scale(self) -> Self {
+        Point(self.0 >> 2, self.1 >> 2)
+    }
+}
+
+impl From<&TouchData> for Point<isize> {
+    fn from(td: &TouchData) -> Self {
+        Self(td.x as _, td.y as _)
+    }
+}
+
+impl From<Point<isize>> for Point<i8> {
+    fn from(p: Point<isize>) -> Self {
+        Point(
+            cmp::min(i8::MAX as isize, cmp::max(p.0, i8::MIN as isize)) as i8,
+            cmp::min(i8::MAX as isize, cmp::max(p.1, i8::MIN as isize)) as i8,
+        )
+    }
+}
+
+pub struct AbsToRel {
+    last_touch: Point<isize>,
+    is_collecting: bool,
+}
+
+impl AbsToRel {
+    pub fn new() -> Self {
+        Self {
+            last_touch: Point(0, 0),
+            is_collecting: false,
+        }
+    }
+
+    pub fn update(&mut self, td: &TouchData) -> Option<Point<i8>> {
+        let p: Point<isize> = td.into();
+        let p = p.scale();
+
+        let res = self.last_touch.delta(p);
+        self.last_touch = p;
+        if self.is_collecting && td.is_pressed {
+            Some(res.into())
+        } else {
+            self.is_collecting = td.is_pressed;
+            None
+        }
+    }
+}
+
+pub struct TrackBall(Point<i8>, i8, u32);
+
+impl TrackBall
+where
+{
+    pub fn new(friction: i8) -> Self {
+        Self(Point(i8::default(), i8::default()), friction, 0)
+    }
+
+    pub fn update(&mut self, point: Option<Point<i8>>, elapsed: u32) -> Point<i8> {
+        if let Some(p) = point {
+            self.0 = p;
+            self.2 = 0;
+        } else {
+            let elapsed = elapsed + self.2;
+            // TODO: configure time divisor
+            let decel: i8 = self.1.saturating_mul((elapsed >> 15).try_into().unwrap_or(i8::MAX));
+            let rem = elapsed & (1 << 15) - 1;
+            self.2 = rem;
+
+            if decel > 0 {
+                let x = Self::abs_add(self.0.0, decel);
+                let y = Self::abs_add(self.0.1, decel);
+                self.0 = Point(x, y);
+            }
+        }
+        self.0
+    }
+
+    fn abs_add(speed: i8, decel: i8) -> i8 {
+        if speed > decel {
+            speed - decel
+        } else if speed < -decel {
+            speed + decel
+        } else {
+            0
+        }
+    }
+}