ezu-core 0.4.0

Core types for ezu: tile/world coordinates, deterministic seeding
Documentation 
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//! Web-Mercator tile / world coordinate utilities.
//!
//! World coordinates are in the unit square `[0, 1] x [0, 1]` covering the whole
//! Web-Mercator projection. This avoids zoom-dependent units and makes
//! deterministic seeding zoom-stable.

/// A Web-Mercator XYZ tile identifier.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub struct TileId {
    pub z: u8,
    pub x: u32,
    pub y: u32,
}

impl TileId {
    pub const fn new(z: u8, x: u32, y: u32) -> Self {
        Self { z, x, y }
    }

    /// Number of tiles along one axis at this zoom level.
    #[inline]
    pub fn axis_tiles(self) -> u32 {
        1u32 << self.z
    }

    /// The tile one zoom level up that contains this tile, or `None`
    /// at zoom 0 (which has no parent).
    #[inline]
    pub fn parent(self) -> Option<TileId> {
        if self.z == 0 {
            None
        } else {
            Some(TileId::new(self.z - 1, self.x >> 1, self.y >> 1))
        }
    }

    /// The ancestor tile at the given (lower) zoom, or `None` if `z`
    /// is greater than or equal to this tile's zoom.
    #[inline]
    pub fn ancestor_at(self, z: u8) -> Option<TileId> {
        if z >= self.z {
            return None;
        }
        let dz = self.z - z;
        Some(TileId::new(z, self.x >> dz, self.y >> dz))
    }

    /// `true` iff `other` lies inside this tile's spatial bounds at a
    /// deeper zoom. A tile is *not* considered its own ancestor.
    pub fn is_ancestor_of(self, other: TileId) -> bool {
        if other.z <= self.z {
            return false;
        }
        let dz = other.z - self.z;
        other.x >> dz == self.x && other.y >> dz == self.y
    }
}

/// A position in the global Web-Mercator unit square `[0, 1] x [0, 1]`.
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct WorldPos {
    pub x: f64,
    pub y: f64,
}

impl WorldPos {
    pub const fn new(x: f64, y: f64) -> Self {
        Self { x, y }
    }
}

/// Convert a tile-local position (in `[0, extent]`) to world unit-square coordinates.
#[inline]
pub fn tile_to_world(tile: TileId, tx: f64, ty: f64, extent: f64) -> WorldPos {
    let n = tile.axis_tiles() as f64;
    WorldPos {
        x: (tile.x as f64 + tx / extent) / n,
        y: (tile.y as f64 + ty / extent) / n,
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn parent_walks_one_level() {
        assert_eq!(TileId::new(0, 0, 0).parent(), None);
        assert_eq!(TileId::new(3, 5, 6).parent(), Some(TileId::new(2, 2, 3)));
    }

    #[test]
    fn ancestor_at_handles_invalid() {
        let t = TileId::new(5, 10, 20);
        assert_eq!(t.ancestor_at(5), None); // same zoom → not an ancestor
        assert_eq!(t.ancestor_at(6), None); // deeper zoom
        assert_eq!(t.ancestor_at(3), Some(TileId::new(3, 2, 5)));
        assert_eq!(t.ancestor_at(0), Some(TileId::new(0, 0, 0)));
    }

    #[test]
    fn is_ancestor_of() {
        let parent = TileId::new(5, 10, 20);
        assert!(parent.is_ancestor_of(TileId::new(7, 41, 81))); // inside
        assert!(!parent.is_ancestor_of(TileId::new(7, 44, 81))); // wrong x branch
        assert!(!parent.is_ancestor_of(parent)); // not self
        assert!(!parent.is_ancestor_of(TileId::new(4, 5, 10))); // ancestor, not descendant
    }
}