Make the line left of indented regions optional (#2636)

* Make the line left of indented regions optional

Controlled with Visuals::indent_has_left_vline

* Add line to changelog

* Fix doclink

CHANGELOG.md

@@ -23,6 +23,7 @@ NOTE: [`epaint`](crates/epaint/CHANGELOG.md), [`eframe`](crates/eframe/CHANGELOG
 * Add `Button::rounding` to enable round buttons ([#2616](https://github.com/emilk/egui/pull/2616)).
 * Add `WidgetVisuals::optional_bg_color` - set it to `Color32::TRANSPARENT` to hide button backgrounds ([#2621](https://github.com/emilk/egui/pull/2621)).
 * Add `Context::screen_rect` and `Context::set_cursor_icon` ([#2625](https://github.com/emilk/egui/pull/2625)).
+* You can turn off the vertical line left of indented regions with `Visuals::indent_has_left_vline` ([#2636](https://github.com/emilk/egui/pull/2636)).
 
 ### Changed 🔧
 * Improved plot grid appearance ([#2412](https://github.com/emilk/egui/pull/2412)).

crates/egui/src/style.rs

@@ -497,6 +497,9 @@ pub struct Visuals {
     /// Show a background behind collapsing headers.
     pub collapsing_header_frame: bool,
 
+    /// Draw a vertical lien left of indented region, in e.g. [`crate::CollapsingHeader`].
+    pub indent_has_left_vline: bool,
+
     /// Wether or not Grids and Tables should be striped by default
     /// (have alternating rows differently colored).
     pub striped: bool,
@@ -752,6 +755,7 @@ impl Visuals {
             clip_rect_margin: 3.0, // should be at least half the size of the widest frame stroke + max WidgetVisuals::expansion
             button_frame: true,
             collapsing_header_frame: false,
+            indent_has_left_vline: true,
 
             striped: false,
         }
@@ -1297,6 +1301,7 @@ impl Visuals {
             clip_rect_margin,
             button_frame,
             collapsing_header_frame,
+            indent_has_left_vline,
 
             striped,
         } = self;
@@ -1354,6 +1359,10 @@ impl Visuals {
 
         ui.checkbox(button_frame, "Button has a frame");
         ui.checkbox(collapsing_header_frame, "Collapsing header has a frame");
+        ui.checkbox(
+            indent_has_left_vline,
+            "Paint a vertical line to the left of indented regions",
+        );
 
         ui.checkbox(striped, "By default, add stripes to grids and tables?");
 

crates/egui/src/ui.rs

@@ -1789,25 +1789,32 @@ impl Ui {
         };
         let ret = add_contents(&mut child_ui);
 
+        let left_vline = self.visuals().indent_has_left_vline;
         let end_with_horizontal_line = self.spacing().indent_ends_with_horizontal_line;
 
+        if left_vline || end_with_horizontal_line {
             if end_with_horizontal_line {
                 child_ui.add_space(4.0);
             }
 
-        // draw a faint line on the left to mark the indented section
             let stroke = self.visuals().widgets.noninteractive.bg_stroke;
             let left_top = child_rect.min - 0.5 * indent * Vec2::X;
             let left_top = self.painter().round_pos_to_pixels(left_top);
             let left_bottom = pos2(left_top.x, child_ui.min_rect().bottom() - 2.0);
             let left_bottom = self.painter().round_pos_to_pixels(left_bottom);
+
+            if left_vline {
+                // draw a faint line on the left to mark the indented section
                 self.painter.line_segment([left_top, left_bottom], stroke);
+            }
+
             if end_with_horizontal_line {
                 let fudge = 2.0; // looks nicer with button rounding in collapsing headers
                 let right_bottom = pos2(child_ui.min_rect().right() - fudge, left_bottom.y);
                 self.painter
                     .line_segment([left_bottom, right_bottom], stroke);
             }
+        }
 
         let response = self.allocate_rect(child_ui.min_rect(), Sense::hover());
         InnerResponse::new(ret, response)