Make layer dragging graphics nicer

lightningbeam-ui/lightningbeam-core/src/actions/mod.rs

@@ -31,6 +31,7 @@ pub mod convert_to_movie_clip;
 pub mod region_split;
 pub mod toggle_group_expansion;
 pub mod group_layers;
+pub mod move_layer;
 
 pub use add_clip_instance::AddClipInstanceAction;
 pub use add_effect::AddEffectAction;
@@ -60,3 +61,4 @@ pub use convert_to_movie_clip::ConvertToMovieClipAction;
 pub use region_split::RegionSplitAction;
 pub use toggle_group_expansion::ToggleGroupExpansionAction;
 pub use group_layers::GroupLayersAction;
+pub use move_layer::MoveLayerAction;

lightningbeam-ui/lightningbeam-core/src/actions/move_layer.rs

@@ -0,0 +1,137 @@
+use crate::action::Action;
+use crate::document::Document;
+use crate::layer::AnyLayer;
+use uuid::Uuid;
+
+/// Action that moves one or more layers to a new position, possibly changing their parent group.
+/// All layers are inserted contiguously into the same target parent.
+/// Handles batch moves atomically: removes all, then inserts all, so indices stay consistent.
+pub struct MoveLayerAction {
+    /// (layer_id, old_parent_id) for each layer to move, in visual order (top to bottom)
+    layers: Vec<(Uuid, Option<Uuid>)>,
+    new_parent_id: Option<Uuid>,
+    /// Insertion index in the new parent's children vec AFTER all dragged layers have been removed
+    new_base_index: usize,
+    /// Stored during execute for rollback: (layer, old_parent_id, old_index_in_parent)
+    removed: Vec<(AnyLayer, Option<Uuid>, usize)>,
+}
+
+impl MoveLayerAction {
+    pub fn new(
+        layers: Vec<(Uuid, Option<Uuid>)>,
+        new_parent_id: Option<Uuid>,
+        new_base_index: usize,
+    ) -> Self {
+        Self {
+            layers,
+            new_parent_id,
+            new_base_index,
+            removed: Vec::new(),
+        }
+    }
+}
+
+fn get_parent_children(
+    document: &mut Document,
+    parent_id: Option<Uuid>,
+) -> Result<&mut Vec<AnyLayer>, String> {
+    match parent_id {
+        None => Ok(&mut document.root.children),
+        Some(id) => {
+            let layer = document
+                .root
+                .get_child_mut(&id)
+                .ok_or_else(|| format!("Parent group {} not found", id))?;
+            match layer {
+                AnyLayer::Group(g) => Ok(&mut g.children),
+                _ => Err(format!("Layer {} is not a group", id)),
+            }
+        }
+    }
+}
+
+impl Action for MoveLayerAction {
+    fn execute(&mut self, document: &mut Document) -> Result<(), String> {
+        self.removed.clear();
+
+        // Phase 1: Remove all layers from their old parents.
+        // Group removals by parent, then remove back-to-front within each parent.
+        // Collect (layer_id, old_parent_id) with their current index.
+        let mut removals: Vec<(Uuid, Option<Uuid>, usize)> = Vec::new();
+        for (layer_id, old_parent_id) in &self.layers {
+            let children = get_parent_children(document, *old_parent_id)?;
+            let idx = children.iter().position(|l| l.id() == *layer_id)
+                .ok_or_else(|| format!("Layer {} not found in parent", layer_id))?;
+            removals.push((*layer_id, *old_parent_id, idx));
+        }
+
+        // Sort by (parent, index) descending so we remove back-to-front
+        removals.sort_by(|a, b| {
+            a.1.cmp(&b.1).then(b.2.cmp(&a.2))
+        });
+
+        let mut removed_layers: Vec<(Uuid, AnyLayer, Option<Uuid>, usize)> = Vec::new();
+        for (layer_id, old_parent_id, idx) in &removals {
+            let children = get_parent_children(document, *old_parent_id)?;
+            let layer = children.remove(*idx);
+            removed_layers.push((*layer_id, layer, *old_parent_id, *idx));
+        }
+
+        // Phase 2: Insert all at new parent, in visual order (self.layers order).
+        // self.new_base_index is the index in the post-removal children vec.
+        let new_children = get_parent_children(document, self.new_parent_id)?;
+        let base = self.new_base_index.min(new_children.len());
+
+        // Insert in forward visual order, all at `base`. Each insert pushes the previous
+        // one to a higher children index. Since the timeline displays children in reverse,
+        // a higher children index = visually higher. So the first visual layer (layers[0])
+        // ends up at the highest children index = visually topmost. Correct.
+        for (layer_id, _) in self.layers.iter() {
+            // Find this layer in removed_layers
+            let pos = removed_layers.iter().position(|(id, _, _, _)| id == layer_id)
+                .ok_or_else(|| format!("Layer {} missing from removed set", layer_id))?;
+            let (_, layer, old_parent_id, old_idx) = removed_layers.remove(pos);
+            self.removed.push((layer.clone(), old_parent_id, old_idx));
+
+            let new_children = get_parent_children(document, self.new_parent_id)?;
+            let insert_at = base.min(new_children.len());
+            new_children.insert(insert_at, layer);
+        }
+
+        Ok(())
+    }
+
+    fn rollback(&mut self, document: &mut Document) -> Result<(), String> {
+        if self.removed.is_empty() {
+            return Err("Cannot rollback: action was not executed".to_string());
+        }
+
+        // Phase 1: Remove all layers from new parent (back-to-front by insertion order).
+        for (layer_id, _) in self.layers.iter().rev() {
+            let new_children = get_parent_children(document, self.new_parent_id)?;
+            let pos = new_children.iter().position(|l| l.id() == *layer_id)
+                .ok_or_else(|| format!("Layer {} not found in new parent for rollback", layer_id))?;
+            new_children.remove(pos);
+        }
+
+        // Phase 2: Re-insert at old positions, sorted by (parent, index) ascending.
+        let mut restore: Vec<(AnyLayer, Option<Uuid>, usize)> = self.removed.drain(..).collect();
+        restore.sort_by(|a, b| a.1.cmp(&b.1).then(a.2.cmp(&b.2)));
+
+        for (layer, old_parent_id, old_idx) in restore {
+            let children = get_parent_children(document, old_parent_id)?;
+            let idx = old_idx.min(children.len());
+            children.insert(idx, layer);
+        }
+
+        Ok(())
+    }
+
+    fn description(&self) -> String {
+        if self.layers.len() == 1 {
+            "Move layer".to_string()
+        } else {
+            format!("Move {} layers", self.layers.len())
+        }
+    }
+}

lightningbeam-ui/lightningbeam-editor/src/main.rs

@@ -6016,7 +6016,7 @@ fn render_pane(
             }
 
             // Icon
-            if let Some(icon) = ctx.icon_cache.get_or_load(tab_type, ui.ctx()) {
+            if let Some(icon) = ctx.shared.icon_cache.get_or_load(tab_type, ui.ctx()) {
                 let icon_texture_id = icon.id();
                 ui.painter().image(
                     icon_texture_id,

lightningbeam-ui/lightningbeam-editor/src/panes/timeline.rs

@@ -145,6 +145,20 @@ enum RecordingType {
     Webcam,
 }
 
+/// State for an in-progress layer header drag-to-reorder operation.
+struct LayerDragState {
+    /// IDs of the layers being dragged (in visual order, top to bottom)
+    layer_ids: Vec<uuid::Uuid>,
+    /// Original parent group IDs for each dragged layer (parallel to layer_ids)
+    source_parent_ids: Vec<Option<uuid::Uuid>>,
+    /// Current gap position in the filtered (dragged-layers-removed) row list
+    gap_row_index: usize,
+    /// Current mouse Y in screen coordinates (for floating header rendering)
+    current_mouse_y: f32,
+    /// Y offset from the top of the topmost dragged row to the mousedown point
+    grab_offset_y: f32,
+}
+
 pub struct TimelinePane {
     /// Horizontal zoom level (pixels per second)
     pixels_per_second: f32,
@@ -189,6 +203,12 @@ pub struct TimelinePane {
     /// Cached egui textures for video thumbnail strip rendering.
     /// Key: (clip_id, thumbnail_timestamp_millis) → TextureHandle
     video_thumbnail_textures: std::collections::HashMap<(uuid::Uuid, i64), egui::TextureHandle>,
+
+    /// Layer header drag-to-reorder state (None if not dragging a layer)
+    layer_drag: Option<LayerDragState>,
+
+    /// Cached mousedown position in header area (for drag threshold detection)
+    header_mousedown_pos: Option<egui::Pos2>,
 }
 
 /// Check if a clip type can be dropped on a layer type
@@ -307,6 +327,43 @@ fn flatten_layer<'a>(
     }
 }
 
+/// Paint a soft drop shadow around a rect using gradient meshes (bottom + right + corner).
+/// Three non-overlapping quads so alpha doesn't double up.
+fn paint_drop_shadow(painter: &egui::Painter, rect: egui::Rect, shadow_size: f32, alpha: u8) {
+    let c = egui::Color32::from_black_alpha(alpha);
+    let t = egui::Color32::TRANSPARENT;
+    let mut mesh = egui::Mesh::default();
+
+    // Bottom edge: straight down, stops at right edge
+    let idx = mesh.vertices.len() as u32;
+    mesh.colored_vertex(rect.left_bottom(), c);                                      // 0
+    mesh.colored_vertex(rect.right_bottom(), c);                                     // 1
+    mesh.colored_vertex(egui::pos2(rect.right(), rect.bottom() + shadow_size), t);   // 2
+    mesh.colored_vertex(egui::pos2(rect.left(), rect.bottom() + shadow_size), t);    // 3
+    mesh.add_triangle(idx, idx + 1, idx + 2);
+    mesh.add_triangle(idx, idx + 2, idx + 3);
+
+    // Right edge: rightward, stops at bottom edge
+    let idx = mesh.vertices.len() as u32;
+    mesh.colored_vertex(rect.right_top(), c);                                        // 0
+    mesh.colored_vertex(egui::pos2(rect.right() + shadow_size, rect.top()), t);      // 1
+    mesh.colored_vertex(egui::pos2(rect.right() + shadow_size, rect.bottom()), t);   // 2
+    mesh.colored_vertex(rect.right_bottom(), c);                                     // 3
+    mesh.add_triangle(idx, idx + 1, idx + 2);
+    mesh.add_triangle(idx, idx + 2, idx + 3);
+
+    // Bottom-right corner: dark at inner corner, transparent at other three
+    let idx = mesh.vertices.len() as u32;
+    mesh.colored_vertex(rect.right_bottom(), c);                                                  // 0
+    mesh.colored_vertex(egui::pos2(rect.right() + shadow_size, rect.bottom()), t);                // 1
+    mesh.colored_vertex(egui::pos2(rect.right() + shadow_size, rect.bottom() + shadow_size), t); // 2
+    mesh.colored_vertex(egui::pos2(rect.right(), rect.bottom() + shadow_size), t);                // 3
+    mesh.add_triangle(idx, idx + 1, idx + 2);
+    mesh.add_triangle(idx, idx + 2, idx + 3);
+
+    painter.add(egui::Shape::mesh(mesh));
+}
+
 /// Shift+click layer selection: toggle a layer in/out of the focus selection,
 /// enforcing the sibling constraint (all selected layers must share the same parent).
 fn shift_toggle_layer(
@@ -428,6 +485,8 @@ impl TimelinePane {
             time_display_format: TimeDisplayFormat::Seconds,
             waveform_upload_progress: std::collections::HashMap::new(),
             video_thumbnail_textures: std::collections::HashMap::new(),
+            layer_drag: None,
+            header_mousedown_pos: None,
         }
     }
 
@@ -1160,11 +1219,27 @@ impl TimelinePane {
         let secondary_text_color = egui::Color32::from_gray(150);
 
         // Build virtual row list (accounts for group expansion)
-        let rows = build_timeline_rows(context_layers);
+        let all_rows = build_timeline_rows(context_layers);
+
+        // When dragging layers, filter them out and compute gap-adjusted positions
+        let drag_layer_ids: Vec<uuid::Uuid> = self.layer_drag.as_ref()
+            .map(|d| d.layer_ids.clone()).unwrap_or_default();
+        let drag_count = drag_layer_ids.len();
+        let gap_row_index = self.layer_drag.as_ref().map(|d| d.gap_row_index);
+
+        // Build filtered row list (excluding dragged layers)
+        let rows: Vec<&TimelineRow> = all_rows.iter()
+            .filter(|r| !drag_layer_ids.contains(&r.layer_id()))
+            .collect();
 
         // Draw layer headers from virtual row list
-        for (i, row) in rows.iter().enumerate() {
-            let y = rect.min.y + i as f32 * LAYER_HEIGHT - self.viewport_scroll_y;
+        for (filtered_i, row) in rows.iter().enumerate() {
+            // Compute Y with gap offset: rows at or after the gap shift down by drag_count * LAYER_HEIGHT
+            let visual_i = match gap_row_index {
+                Some(gap) if filtered_i >= gap => filtered_i + drag_count,
+                _ => filtered_i,
+            };
+            let y = rect.min.y + visual_i as f32 * LAYER_HEIGHT - self.viewport_scroll_y;
 
             // Skip if layer is outside visible area
             if y + LAYER_HEIGHT < rect.min.y || y > rect.max.y {
@@ -1550,6 +1625,100 @@ impl TimelinePane {
             );
         }
 
+        // Draw floating dragged layer headers at mouse position with drop shadow
+        if let Some(ref drag_state) = self.layer_drag {
+            // Collect the dragged rows in order
+            let dragged_rows: Vec<&TimelineRow> = drag_state.layer_ids.iter()
+                .filter_map(|did| all_rows.iter().find(|r| r.layer_id() == *did))
+                .collect();
+
+            let float_top_y = drag_state.current_mouse_y - drag_state.grab_offset_y;
+
+            for (di, dragged_row) in dragged_rows.iter().enumerate() {
+                let float_y = float_top_y + di as f32 * LAYER_HEIGHT;
+                let float_rect = egui::Rect::from_min_size(
+                    egui::pos2(rect.min.x, float_y),
+                    egui::vec2(LAYER_HEADER_WIDTH, LAYER_HEIGHT),
+                );
+
+                // Gradient drop shadow
+                paint_drop_shadow(ui.painter(), float_rect, 8.0, 60);
+
+                // Background (active/selected color)
+                ui.painter().rect_filled(float_rect, 0.0, active_color);
+
+                // Layer info
+                let drag_indent = match dragged_row {
+                    TimelineRow::GroupChild { depth, .. } => *depth as f32 * 16.0,
+                    TimelineRow::CollapsedGroup { depth, .. } => *depth as f32 * 16.0,
+                    _ => 0.0,
+                };
+                let (drag_name, drag_type_str, drag_type_color) = match dragged_row {
+                    TimelineRow::Normal(layer) => {
+                        let (lt, tc) = match layer {
+                            AnyLayer::Vector(_) => ("Vector", egui::Color32::from_rgb(255, 180, 100)),
+                            AnyLayer::Audio(al) => match al.audio_layer_type {
+                                AudioLayerType::Midi => ("MIDI", egui::Color32::from_rgb(100, 255, 150)),
+                                AudioLayerType::Sampled => ("Audio", egui::Color32::from_rgb(100, 180, 255)),
+                            },
+                            AnyLayer::Video(_) => ("Video", egui::Color32::from_rgb(180, 100, 255)),
+                            AnyLayer::Effect(_) => ("Effect", egui::Color32::from_rgb(255, 100, 180)),
+                            AnyLayer::Group(_) => ("Group", egui::Color32::from_rgb(0, 180, 180)),
+                        };
+                        (layer.layer().name.clone(), lt, tc)
+                    }
+                    TimelineRow::CollapsedGroup { group, .. } => {
+                        (group.layer.name.clone(), "Group", egui::Color32::from_rgb(0, 180, 180))
+                    }
+                    TimelineRow::GroupChild { child, .. } => {
+                        let (lt, tc) = match child {
+                            AnyLayer::Vector(_) => ("Vector", egui::Color32::from_rgb(255, 180, 100)),
+                            AnyLayer::Audio(al) => match al.audio_layer_type {
+                                AudioLayerType::Midi => ("MIDI", egui::Color32::from_rgb(100, 255, 150)),
+                                AudioLayerType::Sampled => ("Audio", egui::Color32::from_rgb(100, 180, 255)),
+                            },
+                            AnyLayer::Video(_) => ("Video", egui::Color32::from_rgb(180, 100, 255)),
+                            AnyLayer::Effect(_) => ("Effect", egui::Color32::from_rgb(255, 100, 180)),
+                            AnyLayer::Group(_) => ("Group", egui::Color32::from_rgb(0, 180, 180)),
+                        };
+                        (child.layer().name.clone(), lt, tc)
+                    }
+                };
+
+                // Color indicator bar
+                let indicator_rect = egui::Rect::from_min_size(
+                    float_rect.min + egui::vec2(drag_indent, 0.0),
+                    egui::vec2(4.0, LAYER_HEIGHT),
+                );
+                ui.painter().rect_filled(indicator_rect, 0.0, drag_type_color);
+
+                // Layer name
+                let name_x = 10.0 + drag_indent;
+                ui.painter().text(
+                    float_rect.min + egui::vec2(name_x, 10.0),
+                    egui::Align2::LEFT_TOP,
+                    &drag_name,
+                    egui::FontId::proportional(14.0),
+                    text_color,
+                );
+
+                // Type label
+                ui.painter().text(
+                    float_rect.min + egui::vec2(name_x, 28.0),
+                    egui::Align2::LEFT_TOP,
+                    drag_type_str,
+                    egui::FontId::proportional(11.0),
+                    secondary_text_color,
+                );
+
+                // Separator line at bottom
+                ui.painter().line_segment(
+                    [egui::pos2(float_rect.min.x, float_rect.max.y), egui::pos2(float_rect.max.x, float_rect.max.y)],
+                    egui::Stroke::new(1.0, egui::Color32::from_gray(20)),
+                );
+            }
+        }
+
         // Right border for header column
         ui.painter().line_segment(
             [
@@ -1602,11 +1771,64 @@ impl TimelinePane {
         }
 
         // Build virtual row list (accounts for group expansion)
-        let rows = build_timeline_rows(context_layers);
+        let all_rows = build_timeline_rows(context_layers);
 
-        // Draw layer rows from virtual row list
-        for (i, row) in rows.iter().enumerate() {
-            let y = rect.min.y + i as f32 * LAYER_HEIGHT - self.viewport_scroll_y;
+        // When dragging layers, compute remapped Y positions:
+        // - Dragged rows render at the gap position
+        // - Non-dragged rows shift around the gap
+        let drag_layer_ids_content: Vec<uuid::Uuid> = self.layer_drag.as_ref()
+            .map(|d| d.layer_ids.clone()).unwrap_or_default();
+        let drag_count_content = drag_layer_ids_content.len();
+        let gap_row_index_content = self.layer_drag.as_ref().map(|d| d.gap_row_index);
+
+        // Pre-compute Y position for each row.
+        // Dragged rows follow the mouse continuously (matching the floating header);
+        // non-dragged rows snap to discrete positions shifted around the gap.
+        let drag_float_top_y: Option<f32> = self.layer_drag.as_ref()
+            .map(|d| d.current_mouse_y - d.grab_offset_y);
+
+        let row_y_positions: Vec<f32> = {
+            let mut positions = Vec::with_capacity(all_rows.len());
+            let mut filtered_i = 0usize;
+            let mut drag_offset = 0usize;
+            for row in all_rows.iter() {
+                if drag_layer_ids_content.contains(&row.layer_id()) {
+                    // Dragged row: continuous Y from mouse position
+                    let base_y = drag_float_top_y.unwrap_or(0.0);
+                    positions.push(base_y + drag_offset as f32 * LAYER_HEIGHT);
+                    drag_offset += 1;
+                } else {
+                    // Non-dragged row: discrete position, shifted around gap
+                    let visual = match gap_row_index_content {
+                        Some(gap) if filtered_i >= gap => filtered_i + drag_count_content,
+                        _ => filtered_i,
+                    };
+                    positions.push(rect.min.y + visual as f32 * LAYER_HEIGHT - self.viewport_scroll_y);
+                    filtered_i += 1;
+                }
+            }
+            positions
+        };
+
+        // Draw non-dragged rows first, then dragged rows on top (so shadow/content overlaps correctly)
+        let draw_order: Vec<usize> = {
+            let mut non_dragged: Vec<usize> = Vec::new();
+            let mut dragged: Vec<usize> = Vec::new();
+            for (i, row) in all_rows.iter().enumerate() {
+                if drag_layer_ids_content.contains(&row.layer_id()) {
+                    dragged.push(i);
+                } else {
+                    non_dragged.push(i);
+                }
+            }
+            non_dragged.extend(dragged);
+            non_dragged
+        };
+
+        for &i in &draw_order {
+            let row = &all_rows[i];
+            let y = row_y_positions[i];
+            let is_being_dragged = drag_layer_ids_content.contains(&row.layer_id());
 
             // Skip if layer is outside visible area
             if y + LAYER_HEIGHT < rect.min.y || y > rect.max.y {
@@ -1618,6 +1840,11 @@ impl TimelinePane {
                 egui::vec2(rect.width(), LAYER_HEIGHT),
             );
 
+            // Drop shadow for dragged rows
+            if is_being_dragged {
+                paint_drop_shadow(painter, layer_rect, 8.0, 60);
+            }
+
             let row_layer_id = row.layer_id();
 
             // Active vs inactive background colors
@@ -2793,7 +3020,6 @@ impl TimelinePane {
         context_layers: &[&lightningbeam_core::layer::AnyLayer],
         editing_clip_id: Option<&uuid::Uuid>,
     ) {
-        // Don't allocate the header area for input - let widgets handle it directly
         // Only allocate content area (ruler + layers) with click and drag
         let content_response = ui.allocate_rect(
             egui::Rect::from_min_size(
@@ -2913,19 +3139,18 @@ impl TimelinePane {
             }
         }
 
-        // Handle layer header selection (only if no control widget was clicked)
-        // Check for clicks in header area using direct input query
-        let header_clicked = ui.input(|i| {
-            i.pointer.button_clicked(egui::PointerButton::Primary) &&
-            i.pointer.interact_pos().map_or(false, |pos| header_rect.contains(pos))
-        });
+        // Layer header drag-to-reorder (manual pointer tracking, no allocate_rect)
+        let pointer_pos = ui.input(|i| i.pointer.hover_pos());
+        let primary_down = ui.input(|i| i.pointer.button_down(egui::PointerButton::Primary));
+        let primary_pressed = ui.input(|i| i.pointer.button_pressed(egui::PointerButton::Primary));
+        let primary_released = ui.input(|i| i.pointer.button_released(egui::PointerButton::Primary));
 
-        if header_clicked && !alt_held && !clicked_clip_instance && !self.layer_control_clicked {
-            if let Some(pos) = ui.input(|i| i.pointer.interact_pos()) {
+        // Handle layer header selection on mousedown (immediate, not on release)
+        if primary_pressed && !alt_held && !self.layer_control_clicked {
+            if let Some(pos) = pointer_pos {
+                if header_rect.contains(pos) {
                     let relative_y = pos.y - header_rect.min.y + self.viewport_scroll_y;
                     let clicked_layer_index = (relative_y / LAYER_HEIGHT) as usize;
-
-                // Get the layer at this index (using virtual rows for group support)
                     let header_rows = build_timeline_rows(context_layers);
                     if clicked_layer_index < header_rows.len() {
                         let layer_id = header_rows[clicked_layer_index].layer_id();
@@ -2934,10 +3159,194 @@ impl TimelinePane {
                         if shift_held {
                             shift_toggle_layer(focus, layer_id, clicked_parent, &header_rows);
                         } else {
+                            // Only change selection if the clicked layer isn't already selected
+                            let already_selected = match focus {
+                                lightningbeam_core::selection::FocusSelection::Layers(ids) => ids.contains(&layer_id),
+                                _ => false,
+                            };
+                            if !already_selected {
                                 *focus = lightningbeam_core::selection::FocusSelection::Layers(vec![layer_id]);
                             }
                         }
                     }
+                    // Also record for potential drag
+                    self.header_mousedown_pos = Some(pos);
+                }
+            }
+        }
+
+        // Start drag after movement threshold (4px)
+        const LAYER_DRAG_THRESHOLD: f32 = 4.0;
+        if self.layer_drag.is_none() && !self.layer_control_clicked {
+            if let (Some(down_pos), Some(cur_pos)) = (self.header_mousedown_pos, pointer_pos) {
+                if primary_down && (cur_pos - down_pos).length() > LAYER_DRAG_THRESHOLD {
+                    let relative_y = down_pos.y - header_rect.min.y + self.viewport_scroll_y;
+                    let clicked_index = (relative_y / LAYER_HEIGHT) as usize;
+                    let drag_rows = build_timeline_rows(context_layers);
+                    if clicked_index < drag_rows.len() {
+                        // Collect all selected layer IDs (in visual order)
+                        let selected_ids: Vec<uuid::Uuid> = match focus {
+                            lightningbeam_core::selection::FocusSelection::Layers(ids) => {
+                                // Filter to only IDs present in the row list, in visual order
+                                drag_rows.iter()
+                                    .filter(|r| ids.contains(&r.layer_id()))
+                                    .map(|r| r.layer_id())
+                                    .collect()
+                            }
+                            _ => vec![drag_rows[clicked_index].layer_id()],
+                        };
+                        // If clicked layer isn't in selection, just drag that one
+                        let clicked_id = drag_rows[clicked_index].layer_id();
+                        let layer_ids = if selected_ids.contains(&clicked_id) {
+                            selected_ids
+                        } else {
+                            vec![clicked_id]
+                        };
+
+                        // Find source parent IDs for each dragged layer
+                        let source_parent_ids: Vec<Option<uuid::Uuid>> = layer_ids.iter()
+                            .map(|lid| drag_rows.iter().find(|r| r.layer_id() == *lid).and_then(|r| r.parent_id()))
+                            .collect();
+
+                        // Find the visual index of the first dragged layer
+                        let first_drag_visual_idx = drag_rows.iter()
+                            .position(|r| r.layer_id() == layer_ids[0])
+                            .unwrap_or(0);
+
+                        // Compute gap index in the filtered list
+                        let gap_index = drag_rows.iter()
+                            .take(first_drag_visual_idx)
+                            .filter(|r| !layer_ids.contains(&r.layer_id()))
+                            .count();
+
+                        // Grab offset: ensure the clicked layer stays under the cursor
+                        // in the stacked floating header view
+                        let clicked_row_y = header_rect.min.y + clicked_index as f32 * LAYER_HEIGHT - self.viewport_scroll_y;
+                        let clicked_within_drag = layer_ids.iter().position(|id| *id == clicked_id).unwrap_or(0);
+                        let grab_offset = down_pos.y - clicked_row_y + clicked_within_drag as f32 * LAYER_HEIGHT;
+
+                        self.layer_drag = Some(LayerDragState {
+                            layer_ids,
+                            source_parent_ids,
+                            gap_row_index: gap_index,
+                            current_mouse_y: cur_pos.y,
+                            grab_offset_y: grab_offset,
+                        });
+                    }
+                    self.header_mousedown_pos = None; // consumed
+                }
+            }
+        }
+
+        // Update gap position and mouse Y during layer drag
+        if let Some(ref mut drag) = self.layer_drag {
+            if primary_down {
+                if let Some(pos) = pointer_pos {
+                    drag.current_mouse_y = pos.y;
+                    let relative_y = pos.y - drag.grab_offset_y - header_rect.min.y + self.viewport_scroll_y + LAYER_HEIGHT * 0.5;
+                    let all_rows = build_timeline_rows(context_layers);
+                    let filtered_count = all_rows.iter()
+                        .filter(|r| !drag.layer_ids.contains(&r.layer_id()))
+                        .count();
+                    let target = ((relative_y / LAYER_HEIGHT) as usize).min(filtered_count);
+                    drag.gap_row_index = target;
+                }
+                ui.ctx().request_repaint();
+            }
+        }
+
+        // Drop layers on mouse release
+        if self.layer_drag.is_some() && primary_released {
+            let drag = self.layer_drag.take().unwrap();
+
+            // Build the row list to determine where the gap lands
+            let drop_rows = build_timeline_rows(context_layers);
+            let filtered_rows: Vec<&TimelineRow> = drop_rows.iter()
+                .filter(|r| !drag.layer_ids.contains(&r.layer_id()))
+                .collect();
+
+            // Determine target parent from the row above the gap
+            let new_parent_id = if drag.gap_row_index == 0 {
+                None // top of list = root
+            } else {
+                let row_above = &filtered_rows[drag.gap_row_index.min(filtered_rows.len()) - 1];
+                row_above.parent_id()
+            };
+
+            // Compute insertion index in new parent's children vec AFTER dragged layers are removed.
+            // Get the new parent's children, filter out all dragged layers, find where the
+            // row-above falls in that filtered list.
+            let new_children: Vec<uuid::Uuid> = match new_parent_id {
+                None => context_layers.iter().map(|l| l.id()).collect(),
+                Some(pid) => {
+                    if let Some(AnyLayer::Group(g)) = document.root.get_child(&pid) {
+                        g.children.iter().map(|l| l.id()).collect()
+                    } else {
+                        vec![]
+                    }
+                }
+            };
+            let new_children_filtered: Vec<uuid::Uuid> = new_children.iter()
+                .filter(|id| !drag.layer_ids.contains(id))
+                .copied()
+                .collect();
+
+            let new_base_index = if drag.gap_row_index == 0 {
+                // Gap at top = visually topmost position.
+                // Since timeline reverses children, this is the end of the children vec.
+                new_children_filtered.len()
+            } else {
+                let row_above = &filtered_rows[drag.gap_row_index.min(filtered_rows.len()) - 1];
+                let above_id = row_above.layer_id();
+                if let Some(pos) = new_children_filtered.iter().position(|&id| id == above_id) {
+                    // Insert before it in children vec (visually below = lower children index)
+                    pos
+                } else {
+                    new_children_filtered.len()
+                }
+            };
+
+            // Build layer list: (layer_id, old_parent_id) in visual order
+            let layers: Vec<(uuid::Uuid, Option<uuid::Uuid>)> = drag.layer_ids.iter()
+                .zip(drag.source_parent_ids.iter())
+                .map(|(id, pid)| (*id, *pid))
+                .collect();
+
+            // Only create action if something actually changed
+            let anything_changed = layers.iter().enumerate().any(|(i, (lid, old_pid))| {
+                if *old_pid != new_parent_id {
+                    return true;
+                }
+                // Check if position changed within same parent
+                let old_idx = new_children.iter().position(|id| id == lid);
+                let target_idx_in_original = if new_base_index < new_children_filtered.len() {
+                    // Find where new_children_filtered[new_base_index] sits in original
+                    new_children.iter().position(|id| *id == new_children_filtered[new_base_index])
+                        .map(|p| p + i)
+                } else {
+                    Some(0 + i) // inserting at start of children (end of filtered = start of original)
+                };
+                old_idx != target_idx_in_original
+            });
+
+            if anything_changed {
+                pending_actions.push(Box::new(
+                    lightningbeam_core::actions::MoveLayerAction::new(
+                        layers,
+                        new_parent_id,
+                        new_base_index,
+                    ),
+                ));
+            }
+        }
+
+        // Clear header mousedown if released without starting a drag
+        if primary_released {
+            self.header_mousedown_pos = None;
+        }
+        // Cancel layer drag if pointer is no longer down
+        if self.layer_drag.is_some() && !primary_down {
+            self.layer_drag = None;
         }
 
         // Cache mouse position on mousedown (before any dragging)