Add a gizmo-based overlay to show UI node outlines

Cargo.toml

@@ -112,6 +112,9 @@ bevy_ui = [
   "bevy_sprite",
 ]
 
+# Enable the bevy_ui debug overlay
+bevy_ui_debug = ["bevy_internal/bevy_ui_debug"]
+
 # winit window and input backend
 bevy_winit = ["bevy_internal/bevy_winit"]
 

crates/bevy_internal/Cargo.toml

@@ -118,6 +118,9 @@ file_watcher = ["bevy_asset?/file_watcher"]
 # Enables watching embedded files for Bevy Asset hot-reloading
 embedded_watcher = ["bevy_asset?/embedded_watcher"]
 
+# Enable the bevy_ui debug overlay
+bevy_ui_debug = ["bevy_ui?/debug"]
+
 [dependencies]
 # bevy
 bevy_a11y = { path = "../bevy_a11y", version = "0.12.0" }

crates/bevy_ui/Cargo.toml

@@ -8,27 +8,31 @@ repository = "https://github.com/bevyengine/bevy"
 license = "MIT OR Apache-2.0"
 keywords = ["bevy"]
 
+[features]
+default = []
+debug = ["bevy_gizmos", "bevy_core"]
+
 [dependencies]
 # bevy
 bevy_a11y = { path = "../bevy_a11y", version = "0.12.0" }
 bevy_app = { path = "../bevy_app", version = "0.12.0" }
 bevy_asset = { path = "../bevy_asset", version = "0.12.0" }
+bevy_core = { path = "../bevy_core", version = "0.12.0", optional = true }
 bevy_core_pipeline = { path = "../bevy_core_pipeline", version = "0.12.0" }
 bevy_derive = { path = "../bevy_derive", version = "0.12.0" }
 bevy_ecs = { path = "../bevy_ecs", version = "0.12.0" }
+bevy_gizmos = { path = "../bevy_gizmos", version = "0.12.0", optional = true }
 bevy_hierarchy = { path = "../bevy_hierarchy", version = "0.12.0" }
 bevy_input = { path = "../bevy_input", version = "0.12.0" }
 bevy_log = { path = "../bevy_log", version = "0.12.0" }
 bevy_math = { path = "../bevy_math", version = "0.12.0" }
-bevy_reflect = { path = "../bevy_reflect", version = "0.12.0", features = [
-    "bevy",
-] }
+bevy_reflect = { path = "../bevy_reflect", version = "0.12.0", features = ["bevy"] }
 bevy_render = { path = "../bevy_render", version = "0.12.0" }
 bevy_sprite = { path = "../bevy_sprite", version = "0.12.0" }
 bevy_text = { path = "../bevy_text", version = "0.12.0", optional = true }
 bevy_transform = { path = "../bevy_transform", version = "0.12.0" }
-bevy_window = { path = "../bevy_window", version = "0.12.0" }
 bevy_utils = { path = "../bevy_utils", version = "0.12.0" }
+bevy_window = { path = "../bevy_window", version = "0.12.0" }
 
 # other
 taffy = { version = "0.3.10" }

crates/bevy_ui/src/debug_overlay/inset.rs

@@ -0,0 +1,189 @@
+use bevy_gizmos::prelude::Gizmos;
+use bevy_math::{Vec2, Vec2Swizzles};
+use bevy_render::prelude::Color;
+use bevy_transform::prelude::GlobalTransform;
+use bevy_utils::HashMap;
+
+use super::{CameraQuery, LayoutRect};
+
+trait ApproxF32 {
+    fn is(self, other: f32) -> bool;
+}
+impl ApproxF32 for f32 {
+    fn is(self, other: f32) -> bool {
+        let diff = (self - other).abs();
+        diff < 0.001
+    }
+}
+
+fn rect_border_axis(rect: LayoutRect) -> (f32, f32, f32, f32) {
+    let pos = rect.pos;
+    let size = rect.size;
+    let offset = pos + size;
+    (pos.x, offset.x, pos.y, offset.y)
+}
+
+#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Copy, Debug)]
+enum Dir {
+    Start,
+    End,
+}
+impl Dir {
+    const fn increments(self) -> i64 {
+        match self {
+            Dir::Start => 1,
+            Dir::End => -1,
+        }
+    }
+}
+impl From<i64> for Dir {
+    fn from(value: i64) -> Self {
+        if value.is_positive() {
+            Dir::Start
+        } else {
+            Dir::End
+        }
+    }
+}
+/// Collection of axis aligned "lines" (actually just their coordinate on
+/// a given axis).
+#[derive(Debug, Clone)]
+struct DrawnLines {
+    lines: HashMap<i64, Dir>,
+    width: f32,
+}
+#[allow(clippy::cast_precision_loss, clippy::cast_possible_truncation)]
+impl DrawnLines {
+    fn new(width: f32) -> Self {
+        DrawnLines {
+            lines: HashMap::new(),
+            width,
+        }
+    }
+    /// Return `value` offset by as many `increment`s as necessary to make it
+    /// not overlap with already drawn lines.
+    fn inset(&self, value: f32) -> f32 {
+        let scaled = value / self.width;
+        let fract = scaled.fract();
+        let mut on_grid = scaled.floor() as i64;
+        for _ in 0..10 {
+            let Some(dir) = self.lines.get(&on_grid) else {
+                break;
+            };
+            // TODO(clean): This fixes a panic, but I'm not sure how valid this is
+            let Some(added) = on_grid.checked_add(dir.increments()) else {
+                break;
+            };
+            on_grid = added;
+        }
+        ((on_grid as f32) + fract) * self.width
+    }
+    /// Remove a line from the collection of drawn lines.
+    ///
+    /// Typically, we only care for pre-existing lines when drawing the children
+    /// of a container, nothing more. So we remove it after we are done with
+    /// the children.
+    fn remove(&mut self, value: f32, increment: i64) {
+        let mut on_grid = (value / self.width).floor() as i64;
+        loop {
+            // TODO(clean): This fixes a panic, but I'm not sure how valid this is
+            let Some(next_cell) = on_grid.checked_add(increment) else {
+                return;
+            };
+            if !self.lines.contains_key(&next_cell) {
+                self.lines.remove(&on_grid);
+                return;
+            }
+            on_grid = next_cell;
+        }
+    }
+    /// Add a line from the collection of drawn lines.
+    fn add(&mut self, value: f32, increment: i64) {
+        let mut on_grid = (value / self.width).floor() as i64;
+        loop {
+            let old_value = self.lines.insert(on_grid, increment.into());
+            if old_value.is_none() {
+                return;
+            }
+            // TODO(clean): This fixes a panic, but I'm not sure how valid this is
+            let Some(added) = on_grid.checked_add(increment) else {
+                return;
+            };
+            on_grid = added;
+        }
+    }
+}
+
+pub(super) struct InsetGizmo<'w, 's> {
+    draw: Gizmos<'s>,
+    cam: CameraQuery<'w, 's>,
+    known_y: DrawnLines,
+    known_x: DrawnLines,
+}
+impl<'w, 's> InsetGizmo<'w, 's> {
+    pub(super) fn new(draw: Gizmos<'s>, cam: CameraQuery<'w, 's>, line_width: f32) -> Self {
+        InsetGizmo {
+            draw,
+            cam,
+            known_y: DrawnLines::new(line_width),
+            known_x: DrawnLines::new(line_width),
+        }
+    }
+    fn relative(&self, mut position: Vec2) -> Vec2 {
+        let zero = GlobalTransform::IDENTITY;
+        let Ok(cam) = self.cam.get_single() else {
+            return Vec2::ZERO;
+        };
+        if let Some(new_position) = cam.world_to_viewport(&zero, position.extend(0.)) {
+            position = new_position;
+        };
+        position.xy()
+    }
+    fn line_2d(&mut self, mut start: Vec2, mut end: Vec2, color: Color) {
+        if start.x.is(end.x) {
+            start.x = self.known_x.inset(start.x);
+            end.x = start.x;
+        } else if start.y.is(end.y) {
+            start.y = self.known_y.inset(start.y);
+            end.y = start.y;
+        }
+        let (start, end) = (self.relative(start), self.relative(end));
+        self.draw.line_2d(start, end, color);
+    }
+    pub(super) fn set_scope(&mut self, rect: LayoutRect) {
+        let (left, right, top, bottom) = rect_border_axis(rect);
+        self.known_x.add(left, 1);
+        self.known_x.add(right, -1);
+        self.known_y.add(top, 1);
+        self.known_y.add(bottom, -1);
+    }
+    pub(super) fn clear_scope(&mut self, rect: LayoutRect) {
+        let (left, right, top, bottom) = rect_border_axis(rect);
+        self.known_x.remove(left, 1);
+        self.known_x.remove(right, -1);
+        self.known_y.remove(top, 1);
+        self.known_y.remove(bottom, -1);
+    }
+    pub(super) fn rect_2d(&mut self, rect: LayoutRect, color: Color) {
+        let (left, right, top, bottom) = rect_border_axis(rect);
+        if left.is(right) {
+            self.line_2d(Vec2::new(left, top), Vec2::new(left, bottom), color);
+        } else if top.is(bottom) {
+            self.line_2d(Vec2::new(left, top), Vec2::new(right, top), color);
+        } else {
+            let inset_x = |v| self.known_x.inset(v);
+            let inset_y = |v| self.known_y.inset(v);
+            let (left, right) = (inset_x(left), inset_x(right));
+            let (top, bottom) = (inset_y(top), inset_y(bottom));
+            let strip = [
+                Vec2::new(left, top),
+                Vec2::new(left, bottom),
+                Vec2::new(right, bottom),
+                Vec2::new(right, top),
+                Vec2::new(left, top),
+            ];
+            self.draw
+                .linestrip_2d(strip.map(|v| self.relative(v)), color);
+        }
+    }
+}