implementing Fixed constraint

crates/tek_core/src/engine.rs

@@ -385,6 +385,26 @@ impl<T> Align<T> {
     }
 }
 
+/// Enforce fixed size of drawing area
+pub enum Fixed<U: Number, T> {
+    /// Enforce fixed width
+    W(U, T),
+    /// Enforce fixed height
+    H(U, T),
+    /// Enforce fixed width and height
+    WH(U, U, T),
+}
+
+impl<N: Number, T> Fixed<N, T> {
+    pub fn inner (&self) -> &T {
+        match self {
+            Self::W(_, inner) => inner,
+            Self::H(_, inner) => inner,
+            Self::WH(_, _, inner) => inner,
+        }
+    }
+}
+
 /// Enforce minimum size of drawing area
 pub enum Min<U: Number, T> {
     /// Enforce minimum width

crates/tek_core/src/tui.rs

@@ -452,6 +452,31 @@ pub const NOT_DIM_BOLD: Style = Style {
     sub_modifier:    Modifier::DIM,
 };
 
+impl<T: Widget<Engine = Tui>> Widget for Fixed<u16, T> {
+    type Engine = Tui;
+    fn layout (&self, area: [u16;4]) -> Perhaps<[u16;4]> {
+        Ok(match self {
+            Self::W(w, item) => if area.w() < *w { None } else {
+                item.layout(area)?.map(|[x, y, _, h]|[x, y, *w, h])
+            },
+            Self::H(h, item) => if area.w() < *h { None } else {
+                item.layout(area)?.map(|[x, y, w, _]|[x, y, w, *h])
+            },
+            Self::WH(w, h, item) => if area.w() < *w || area.h() < *h { None } else {
+                item.layout(area)?.map(|[x, y, _, _]|[x, y, *w, *h])
+            }
+        })
+    }
+    fn render (&self, to: &mut Tui) -> Perhaps<[u16;4]> {
+        // 🡘  🡙 ←🡙→
+        if let Some(area) = self.layout(to.area())? {
+            to.render_in(area, self.inner())
+        } else {
+            Ok(None)
+        }
+    }
+}
+
 impl<F> Widget for Split<Tui, F>
 where
     F: Send + Sync + Fn(&mut dyn FnMut(&dyn Widget<Engine = Tui>)->Usually<()>)->Usually<()>