Add more methods to direction (#5893)

crates/typst-library/src/layout/dir.rs

@@ -50,6 +50,42 @@ impl Dir {
     pub const TTB: Self = Self::TTB;
     pub const BTT: Self = Self::BTT;
 
+    /// Returns a direction from a starting point.
+    ///
+    /// ```example
+    /// direction.from(left) \
+    /// direction.from(right) \
+    /// direction.from(top) \
+    /// direction.from(bottom)
+    /// ```
+    #[func]
+    pub const fn from(side: Side) -> Dir {
+        match side {
+            Side::Left => Self::LTR,
+            Side::Right => Self::RTL,
+            Side::Top => Self::TTB,
+            Side::Bottom => Self::BTT,
+        }
+    }
+
+    /// Returns a direction from an end point.
+    ///
+    /// ```example
+    /// direction.to(left) \
+    /// direction.to(right) \
+    /// direction.to(top) \
+    /// direction.to(bottom)
+    /// ```
+    #[func]
+    pub const fn to(side: Side) -> Dir {
+        match side {
+            Side::Right => Self::LTR,
+            Side::Left => Self::RTL,
+            Side::Bottom => Self::TTB,
+            Side::Top => Self::BTT,
+        }
+    }
+
     /// The axis this direction belongs to, either `{"horizontal"}` or
     /// `{"vertical"}`.
     ///
@@ -65,6 +101,22 @@ impl Dir {
         }
     }
 
+    /// The corresponding sign, for use in calculations.
+    ///
+    /// ```example
+    /// #ltr.sign() \
+    /// #rtl.sign() \
+    /// #ttb.sign() \
+    /// #btt.sign()
+    /// ```
+    #[func]
+    pub const fn sign(self) -> i64 {
+        match self {
+            Self::LTR | Self::TTB => 1,
+            Self::RTL | Self::BTT => -1,
+        }
+    }
+
     /// The start point of this direction, as an alignment.
     ///
     /// ```example

tests/suite/layout/dir.typ

@@ -1,10 +1,35 @@
+--- dir-from ---
+#test(direction.from(left), ltr)
+#test(direction.from(right), rtl)
+#test(direction.from(top), ttb)
+#test(direction.from(bottom), btt)
+
+--- dir-from-invalid ---
+// Error: 17-23 cannot convert this alignment to a side
+#direction.from(center)
+
+--- dir-to ---
+#test(direction.to(left), rtl)
+#test(direction.to(right), ltr)
+#test(direction.to(top), btt)
+#test(direction.to(bottom), ttb)
+
+-- dir-to-invalid ---
+// Error: 15-21 cannot convert this alignment to a side
+#direction.to(center)
+
 --- dir-axis ---
-// Test direction methods.
 #test(ltr.axis(), "horizontal")
 #test(rtl.axis(), "horizontal")
 #test(ttb.axis(), "vertical")
 #test(btt.axis(), "vertical")
 
+--- dir-sign ---
+#test(ltr.sign(), 1)
+#test(rtl.sign(), -1)
+#test(ttb.sign(), 1)
+#test(btt.sign(), -1)
+
 --- dir-start ---
 #test(ltr.start(), left)
 #test(rtl.start(), right)