Allow negative shadow spread

niri-config/src/lib.rs

@@ -711,7 +711,7 @@ pub struct Shadow {
     #[knuffel(child, unwrap(argument), default = Self::default().softness)]
     pub softness: FloatOrInt<0, 1024>,
     #[knuffel(child, unwrap(argument), default = Self::default().spread)]
-    pub spread: FloatOrInt<0, 1024>,
+    pub spread: FloatOrInt<-1024, 1024>,
     #[knuffel(child, unwrap(argument), default = Self::default().draw_behind_window)]
     pub draw_behind_window: bool,
     #[knuffel(child, default = Self::default().color)]
@@ -1379,7 +1379,7 @@ pub struct ShadowRule {
     #[knuffel(child, unwrap(argument))]
     pub softness: Option<FloatOrInt<0, 1024>>,
     #[knuffel(child, unwrap(argument))]
-    pub spread: Option<FloatOrInt<0, 1024>>,
+    pub spread: Option<FloatOrInt<-1024, 1024>>,
     #[knuffel(child, unwrap(argument))]
     pub draw_behind_window: Option<bool>,
     #[knuffel(child)]
@@ -2346,6 +2346,7 @@ impl CornerRadius {
     }
 
     pub fn expanded_by(mut self, width: f32) -> Self {
+        // Radius = 0 is preserved, so that square corners remain square.
         if self.top_left > 0. {
             self.top_left += width;
         }
@@ -2359,6 +2360,13 @@ impl CornerRadius {
             self.bottom_left += width;
         }
 
+        if width < 0. {
+            self.top_left = self.top_left.max(0.);
+            self.top_right = self.top_right.max(0.);
+            self.bottom_left = self.bottom_left.max(0.);
+            self.bottom_right = self.bottom_right.max(0.);
+        }
+
         self
     }
 

src/layout/shadow.rs

@@ -57,12 +57,18 @@ impl Shadow {
         let offset = self.config.offset;
         let offset = Point::from((ceil(offset.x.0), ceil(offset.y.0)));
 
-        let spread = ceil(self.config.spread.0);
+        let spread = self.config.spread.0;
+        let spread = ceil(spread.abs()).copysign(spread);
         let offset = offset - Point::from((spread, spread));
 
         let win_radius = radius.fit_to(win_size.w as f32, win_size.h as f32);
 
-        let box_size = win_size + Size::from((spread, spread)).upscale(2.);
+        let box_size = if spread >= 0. {
+            win_size + Size::from((spread, spread)).upscale(2.)
+        } else {
+            // This is a saturating sub.
+            win_size - Size::from((-spread, -spread)).upscale(2.)
+        };
         let radius = win_radius.expanded_by(spread as f32);
 
         let shader_size = box_size + Size::from((width, width)).upscale(2.);

wiki/Configuration:-Layout.md

@@ -372,6 +372,7 @@ Set `on` to enable the shadow.
 Setting `softness 0` will give you hard shadows.
 
 `spread` is the distance to expand the window rectangle in logical pixels, same as [CSS box-shadow] spread.
+<sup>Since: next release</sup> Spread can be negative.
 
 `offset` moves the shadow relative to the window in logical pixels, same as [CSS box-shadow] offset.
 For example, `offset x=2 y=2` will move the shadow 2 logical pixels downwards and to the right.