1 files changed, 86 insertions, 1 deletions
diff --git a/helix-view/src/graphics.rs b/helix-view/src/graphics.rs
index 9a7a86c3..66013ee5 100644
--- a/helix-view/src/graphics.rs
+++ b/helix-view/src/graphics.rs
@@ -24,7 +24,7 @@ pub struct Margin {
 }
 
 /// A simple rectangle used in the computation of the layout and to give widgets an hint about the
-/// area they are supposed to render to.
+/// area they are supposed to render to. (x, y) = (0, 0) is at the top left corner of the screen.
 #[derive(Debug, Clone, Copy, Hash, PartialEq, Eq)]
 pub struct Rect {
     pub x: u16,
@@ -92,6 +92,57 @@ impl Rect {
         self.y.saturating_add(self.height)
     }
 
+    // Returns a new Rect with width reduced from the left side.
+    // This changes the `x` coordinate and clamps it to the right
+    // edge of the original Rect.
+    pub fn clip_left(self, width: u16) -> Rect {
+        let width = std::cmp::min(width, self.width);
+        Rect {
+            x: self.x.saturating_add(width),
+            width: self.width.saturating_sub(width),
+            ..self
+        }
+    }
+
+    // Returns a new Rect with width reduced from the right side.
+    // This does _not_ change the `x` coordinate.
+    pub fn clip_right(self, width: u16) -> Rect {
+        Rect {
+            width: self.width.saturating_sub(width),
+            ..self
+        }
+    }
+
+    // Returns a new Rect with height reduced from the top.
+    // This changes the `y` coordinate and clamps it to the bottom
+    // edge of the original Rect.
+    pub fn clip_top(self, height: u16) -> Rect {
+        let height = std::cmp::min(height, self.height);
+        Rect {
+            y: self.y.saturating_add(height),
+            height: self.height.saturating_sub(height),
+            ..self
+        }
+    }
+
+    // Returns a new Rect with height reduced from the bottom.
+    // This does _not_ change the `y` coordinate.
+    pub fn clip_bottom(self, height: u16) -> Rect {
+        Rect {
+            height: self.height.saturating_sub(height),
+            ..self
+        }
+    }
+
+    pub fn with_height(self, height: u16) -> Rect {
+        // new height may make area > u16::max_value, so use new()
+        Self::new(self.x, self.y, self.width, height)
+    }
+
+    pub fn with_width(self, width: u16) -> Rect {
+        Self::new(self.x, self.y, width, self.height)
+    }
+
     pub fn inner(self, margin: &Margin) -> Rect {
         if self.width < 2 * margin.horizontal || self.height < 2 * margin.vertical {
             Rect::default()
@@ -495,6 +546,40 @@ mod tests {
         assert_eq!(rect.height, 100);
     }
 
+    #[test]
+    fn test_rect_chop_from_left() {
+        let rect = Rect::new(0, 0, 20, 30);
+        assert_eq!(Rect::new(10, 0, 10, 30), rect.clip_left(10));
+        assert_eq!(
+            Rect::new(20, 0, 0, 30),
+            rect.clip_left(40),
+            "x should be clamped to original width if new width is bigger"
+        );
+    }
+
+    #[test]
+    fn test_rect_chop_from_right() {
+        let rect = Rect::new(0, 0, 20, 30);
+        assert_eq!(Rect::new(0, 0, 10, 30), rect.clip_right(10));
+    }
+
+    #[test]
+    fn test_rect_chop_from_top() {
+        let rect = Rect::new(0, 0, 20, 30);
+        assert_eq!(Rect::new(0, 10, 20, 20), rect.clip_top(10));
+        assert_eq!(
+            Rect::new(0, 30, 20, 0),
+            rect.clip_top(50),
+            "y should be clamped to original height if new height is bigger"
+        );
+    }
+
+    #[test]
+    fn test_rect_chop_from_bottom() {
+        let rect = Rect::new(0, 0, 20, 30);
+        assert_eq!(Rect::new(0, 0, 20, 20), rect.clip_bottom(10));
+    }
+
     fn styles() -> Vec<Style> {
         vec![
             Style::default(),