Add Rect::ZERO and make stuff const

Also tweaks the comments because they're not worth a separate commit.

showbits-common/src/rect.rs

@@ -11,9 +11,12 @@ pub struct Rect {
 }
 
 impl Rect {
-    /// Whenever a `Rect` is constructed, this function must be used. This
+    /// A zero-sized rectangle located at the origin.
+    pub const ZERO: Self = Self::new(0, 0, -1, -1);
+
+    /// Whenever a rectangle is constructed, this function must be used. This
     /// ensures invariants are always checked.
-    fn new(north: i32, south: i32, west: i32, east: i32) -> Self {
+    const fn new(north: i32, south: i32, west: i32, east: i32) -> Self {
         let result = Self {
             north,
             south,
@@ -28,65 +31,65 @@ impl Rect {
         result
     }
 
-    /// Construct a `Rect` that is a bounding box around two points.
+    /// Construct a rectangle that is a bounding box around two points.
     ///
-    /// It is not possible to construct a `Rect` with a width or height of 0
+    /// It is not possible to construct a rectangle with a width or height of 0
     /// through this method. Use one of the other constructor functions instead.
     pub fn from_points(a: Vec2, b: Vec2) -> Self {
         Self::new(a.y.min(b.y), a.y.max(b.y), a.x.min(b.x), a.x.max(b.x))
     }
 
-    /// Construct a `Rect` from its north-west and south-east corners.
-    pub fn from_nw_se(nw: Vec2, se: Vec2) -> Self {
+    /// Construct a rectangle from its north-west and south-east corners.
+    pub const fn from_nw_se(nw: Vec2, se: Vec2) -> Self {
         Self::new(nw.y, se.y, nw.x, se.x)
     }
 
-    /// Construct a `Rect` from its north-east and south-west corners.
-    pub fn from_ne_sw(ne: Vec2, sw: Vec2) -> Self {
+    /// Construct a rectangle from its north-east and south-west corners.
+    pub const fn from_ne_sw(ne: Vec2, sw: Vec2) -> Self {
         Self::new(ne.y, sw.y, sw.x, ne.x)
     }
 
-    /// Construct a `Rect` from its north-west corner and size.
+    /// Construct a rectangle from its north-west corner and size.
     pub fn from_nw(nw: Vec2, size: Vec2) -> Self {
         let se = nw + (size - 1);
         Self::from_nw_se(nw, se)
     }
 
-    /// Construct a `Rect` from its north-east corner and size.
+    /// Construct a rectangle from its north-east corner and size.
     pub fn from_corner_ne(ne: Vec2, size: Vec2) -> Self {
         let sw = ne + (size - 1).neg_x();
         Self::from_ne_sw(ne, sw)
     }
 
-    /// Construct a `Rect` from its south-west corner and size.
+    /// Construct a rectangle from its south-west corner and size.
     pub fn from_corner_sw(sw: Vec2, size: Vec2) -> Self {
         let ne = sw + (size - 1).neg_y();
         Self::from_ne_sw(ne, sw)
     }
 
-    /// Construct a `Rect` from its south-east corner and size.
+    /// Construct a rectangle from its south-east corner and size.
     pub fn from_corner_se(se: Vec2, size: Vec2) -> Self {
         let nw = se - (size - 1);
         Self::from_nw_se(nw, se)
     }
 
-    pub fn corner_nw(&self) -> Vec2 {
+    pub const fn corner_nw(&self) -> Vec2 {
         Vec2::new(self.west, self.north)
     }
 
-    pub fn corner_ne(&self) -> Vec2 {
+    pub const fn corner_ne(&self) -> Vec2 {
         Vec2::new(self.east, self.north)
     }
 
-    pub fn corner_sw(&self) -> Vec2 {
+    pub const fn corner_sw(&self) -> Vec2 {
         Vec2::new(self.west, self.south)
     }
 
-    pub fn corner_se(&self) -> Vec2 {
+    pub const fn corner_se(&self) -> Vec2 {
         Vec2::new(self.east, self.south)
     }
 
-    pub fn size(&self) -> Vec2 {
+    pub const fn size(&self) -> Vec2 {
         Vec2::new(self.east - self.west + 1, self.south - self.north + 1)
     }
 }