Add collision groups to filter collision pairs.

src/geometry/interaction_groups.rs

@@ -0,0 +1,54 @@
+#[repr(transparent)]
+#[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
+#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
+/// Pairwise filtering using bit masks.
+///
+/// This filtering method is based on two 16-bit values:
+/// - The interaction groups (the 16 left-most bits of `self.0`).
+/// - The interaction mask (the 16 right-most bits of `self.0`).
+///
+/// An interaction is allowed between two filters `a` and `b` two conditions
+/// are met simultaneously:
+/// - The interaction groups of `a` has at least one bit set to `1` in common with the interaction mask of `b`.
+/// - The interaction groups of `b` has at least one bit set to `1` in common with the interaction mask of `a`.
+/// In other words, interactions are allowed between two filter iff. the following condition is met:
+/// ```rust
+/// ((self.0 >> 16) & rhs.0) != 0 && ((rhs.0 >> 16) & self.0) != 0
+/// ```
+pub struct InteractionGroups(pub u32);
+
+impl InteractionGroups {
+    /// Allow interaction with everything.
+    pub fn all() -> Self {
+        Self(u32::MAX)
+    }
+
+    /// Prevent all interactions.
+    pub fn none() -> Self {
+        Self(0)
+    }
+
+    /// Sets the group this filter is part of.
+    pub fn with_groups(self, groups: u16) -> Self {
+        Self((self.0 & 0x0000ffff) | ((groups as u32) << 16))
+    }
+
+    /// Sets the interaction mask of this filter.
+    pub fn with_mask(self, mask: u16) -> Self {
+        Self((self.0 & 0xffff0000) | (mask as u32))
+    }
+
+    /// Check if interactions should be allowed based on the interaction groups and mask.
+    ///
+    /// An interaction is allowed iff. the groups of `self` contain at least one bit set to 1 in common
+    /// with the mask of `rhs`, and vice-versa.
+    pub fn test(self, rhs: Self) -> bool {
+        ((self.0 >> 16) & rhs.0) != 0 && ((rhs.0 >> 16) & self.0) != 0
+    }
+}
+
+impl Default for InteractionGroups {
+    fn default() -> Self {
+        Self::all()
+    }
+}