[grid] Allow putting a separator in a grid

egui/src/grid.rs

@@ -82,15 +82,25 @@ impl GridLayout {
     }
 
     pub(crate) fn available_rect(&self, region: &Region) -> Rect {
-        let mut rect = Rect::from_min_max(region.cursor, region.max_rect.max);
-        rect.set_height(rect.height().at_least(self.min_row_height));
-        rect
+        // let mut rect = Rect::from_min_max(region.cursor, region.max_rect.max);
+        // rect.set_height(rect.height().at_least(self.min_row_height));
+        // rect
+        self.available_rect_finite(region)
     }
 
     pub(crate) fn available_rect_finite(&self, region: &Region) -> Rect {
-        let mut rect = Rect::from_min_max(region.cursor, region.max_rect_finite().max);
-        rect.set_height(rect.height().at_least(self.min_row_height));
-        rect
+        // If we want to allow width-filling widgets like `Separator` in one of the first cells
+        // then we need to make sure they don't spill out of the first cell:
+        let width = self
+            .prev_state
+            .col_width(self.col)
+            .or_else(|| self.curr_state.col_width(self.col))
+            .unwrap_or_default();
+        let height = region
+            .max_rect_finite()
+            .height()
+            .at_least(self.min_row_height);
+        Rect::from_min_size(region.cursor, vec2(width, height))
     }
 
     pub(crate) fn next_cell(&self, cursor: Pos2, child_size: Vec2) -> Rect {

egui/src/placer.rs

@@ -27,6 +27,10 @@ impl Placer {
         }
     }
 
+    pub(crate) fn is_grid(&self) -> bool {
+        self.grid.is_some()
+    }
+
     pub(crate) fn layout(&self) -> &Layout {
         &self.layout
     }

egui/src/ui.rs

@@ -1118,6 +1118,10 @@ impl Ui {
         self.placer.save_grid();
     }
 
+    pub(crate) fn is_grid(&self) -> bool {
+        self.placer.is_grid()
+    }
+
     /// Move to the next row in a grid layout or wrapping layout.
     /// Otherwise does nothing.
     pub fn end_row(&mut self) {

egui/src/widgets/separator.rs

@@ -45,8 +45,8 @@ impl Widget for Separator {
             is_horizontal_line,
         } = self;
 
-        let is_horizontal_line =
-            is_horizontal_line.unwrap_or_else(|| !ui.layout().main_dir().is_horizontal());
+        let is_horizontal_line = is_horizontal_line
+            .unwrap_or_else(|| ui.is_grid() || !ui.layout().main_dir().is_horizontal());
 
         let available_space = ui.available_size_before_wrap_finite();
 

egui_demo_lib/src/apps/demo/widget_gallery.rs

@@ -35,7 +35,6 @@ impl super::Demo for WidgetGallery {
     fn show(&mut self, ctx: &egui::CtxRef, open: &mut bool) {
         egui::Window::new(self.name())
             .open(open)
-            .default_width(200.0)
             .resizable(false)
             .show(ctx, |ui| {
                 use super::View;
@@ -131,9 +130,7 @@ impl super::View for WidgetGallery {
             ui.end_row();
 
             ui.label("Separator:");
-            // Putting a separator in a grid is kind of meaningless since there is no well-defined direction.
-            // Normally you'd just do ui.separator(), but here we need to explicitly pick a dimension:
-            ui.add(egui::Separator::new().horizontal());
+            ui.separator();
             ui.end_row();
 
             ui.label("CollapsingHeader:");