Add support for asymmetrical padding

core/src/padding.rs

@@ -0,0 +1,65 @@
+/// An amount of space to pad for each side of a box
+#[derive(Debug, Hash, Copy, Clone)]
+pub struct Padding {
+    /// Top padding
+    pub top: u16,
+    /// Right padding
+    pub right: u16,
+    /// Bottom padding
+    pub bottom: u16,
+    /// Left padding
+    pub left: u16,
+}
+
+impl Padding {
+    /// Padding of zero
+    pub const ZERO: Padding = Padding {
+        top: 0,
+        right: 0,
+        bottom: 0,
+        left: 0,
+    };
+
+    /// Create a Padding that is equal on all sides
+    pub const fn new(padding: u16) -> Padding {
+        Padding {
+            top: padding,
+            right: padding,
+            bottom: padding,
+            left: padding,
+        }
+    }
+}
+
+impl std::convert::From<u16> for Padding {
+    fn from(p: u16) -> Self {
+        Padding {
+            top: p,
+            right: p,
+            bottom: p,
+            left: p,
+        }
+    }
+}
+
+impl std::convert::From<[u16; 2]> for Padding {
+    fn from(p: [u16; 2]) -> Self {
+        Padding {
+            top: p[0],
+            right: p[1],
+            bottom: p[0],
+            left: p[1],
+        }
+    }
+}
+
+impl std::convert::From<[u16; 4]> for Padding {
+    fn from(p: [u16; 4]) -> Self {
+        Padding {
+            top: p[0],
+            right: p[1],
+            bottom: p[2],
+            left: p[3],
+        }
+    }
+}