diff -r a4dd3d307115 -r a4c17cfaa4c9 rust/hwphysics/src/collision.rs
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/rust/hwphysics/src/collision.rs	Fri Nov 09 01:05:34 2018 +0300
@@ -0,0 +1,111 @@
+use std::{
+    ops::RangeInclusive
+};
+
+use crate::{
+    common::GearId,
+    physics::PhysicsData,
+    grid::Grid
+};
+
+use fpnum::*;
+use integral_geometry::{
+    Point, Size, GridIndex
+};
+use land2d::Land2D;
+
+pub fn fppoint_round(point: &FPPoint) -> Point {
+    Point::new(point.x().round() as i32, point.y().round() as i32)
+}
+
+#[derive(PartialEq, Eq, Clone, Copy, Debug)]
+pub struct CircleBounds {
+    pub center: FPPoint,
+    pub radius: FPNum
+}
+
+impl CircleBounds {
+    pub fn intersects(&self, other: &CircleBounds) -> bool {
+        (other.center - self.center).is_in_range(self.radius + other.radius)
+    }
+
+    pub fn rows(&self) -> impl Iterator<Item = (usize, RangeInclusive<usize>)> {
+        let radius = self.radius.abs_round() as usize;
+        let center = Point::from_fppoint(&self.center);
+        (center.y as usize - radius..=center.y as usize + radius)
+            .map(move |row| (row, center.x as usize - radius..=center.x as usize + radius))
+    }
+}
+
+#[derive(PartialEq, Eq, Clone, Copy, Debug)]
+pub struct CollisionData {
+    pub bounds: CircleBounds
+}
+
+#[derive(PartialEq, Eq, Clone, Copy, Debug)]
+pub struct ContactData {
+    pub elasticity: FPNum,
+    pub friction: FPNum
+}
+
+struct EnabledCollisionsCollection {
+    gear_ids: Vec<GearId>,
+    collisions: Vec<CollisionData>
+}
+
+impl EnabledCollisionsCollection {
+    fn push(&mut self, gear_id: GearId, collision: CollisionData) {
+        self.gear_ids.push(gear_id);
+        self.collisions.push(collision);
+    }
+
+    fn iter(&self) -> impl Iterator<Item = (GearId, &CollisionData)> {
+        self.gear_ids.iter().cloned().zip(self.collisions.iter())
+    }
+}
+
+pub struct CollisionProcessor {
+    grid: Grid,
+    enabled_collisions: EnabledCollisionsCollection,
+
+    detected_collisions: DetectedCollisions,
+}
+
+pub struct DetectedCollisions {
+    pub pairs: Vec<(GearId, GearId)>,
+    pub positions: Vec<Point>
+}
+
+impl DetectedCollisions {
+    pub fn new(capacity: usize) -> Self {
+        Self {
+            pairs: Vec::with_capacity(capacity),
+            positions: Vec::with_capacity(capacity),
+        }
+    }
+
+    pub fn push(&mut self, contact_gear_id1: GearId, contact_gear_id2: GearId, position: &FPPoint) {
+        self.pairs.push((contact_gear_id1, contact_gear_id2));
+        self.positions.push(fppoint_round(position));
+    }
+}
+
+impl CollisionProcessor {
+    pub fn process(&mut self, land: &Land2D<u32>, updates: &crate::physics::PositionUpdate) {
+        self.grid.check_collisions(&mut self.detected_collisions);
+
+        for (gear_id, collision) in self.enabled_collisions.iter() {
+            if collision.bounds.rows().any(|(y, r)| (&land[y][r]).iter().any(|v| *v != 0)) {
+                self.detected_collisions.push(0, 0, &collision.bounds.center)
+            }
+        }
+    }
+
+    pub fn push(&mut self, gear_id: GearId, physics_data: PhysicsData, collision_data: CollisionData) {
+        if physics_data.velocity.is_zero() {
+            self.grid.insert_static(0, &physics_data.position, &collision_data.bounds);
+        } else {
+            self.grid.insert_dynamic(0, &physics_data.position, &collision_data.bounds);
+        }
+    }
+}
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